Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/20/21
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
840 PM CDT Thu Aug 19 2021
.UPDATE...
Issued at 839 PM CDT Thu Aug 19 2021
Made some updates to pops for the overnight period based on
current radar trends and the latest HRRR runs. Overall forecast is
on track. Not sure there`ll be much for severe overnight, isolated
at best given a remaining lack of deep layer shear for much of the
CWA.
&&
.SHORT TERM...(This Evening through Friday Night)
Issued at 338 PM CDT Thu Aug 19 2021
Surface boundary in central sd has pushed back west as winds turned
southeast as surface pressure falls occurred. The ops models and
ensembles all show two significant areas of lift affecting our
region tonight through Friday night. The first short wave trough
lifting into the region from the southwest was showing shower and
storm development into western Nebraska/western South Dakota this
afternoon. The hi-res models and ops models show this activity
expanding into this evening and overnight into our cwa. Many of the
hi-res models show the activity making it to the James Valley and
breaking up quite a bit. At any rate, the slight risk of severe
weather was expanded earlier into central sd for tonight as the deep
layer shear will be a little better along with instability. All
indications are that low clouds will move in/form tonight across
much of the region. These low clouds and how much and when they
break up on Friday will be key to weakening the cap and increasing
instability with surface heating. Otherwise, the main upper level
low pressure trough will make its way into and across the region
Friday and Friday night. This strong system will bring strong ll and
mid level wind shear. Therefore, expect storms to redevelop on
Friday as the lift from this system moves in and a cold front sweeps
quickly east. At this time, there is a slight risk of severe weather
mainly east of the James Valley for Friday and Friday evening. These
storms could produce large hail, damaging winds, along with a
possible tornado. Have in high pops for tonight into Friday evening.
It will also be cooler on Friday with 70s and lower 80s for highs.
.LONG TERM...(Saturday through Thursday)
Issued at 338 PM CDT Thu Aug 19 2021
A few lingering showers could be set up over our far northeastern
counties. With the upper level low/trough already well to our north,
and southwesterly flow already by mid morning, expected limited
additional chances for shower or thunderstorm activity. The next
chance of precipitation looks to move in mainly during the daylight
hours Sunday. This will be while a surface low tracks across ND as a
500mb trough mainly stays to our north. The main concern will be for
any storms developing along the frontal boundary, with the better
instability along the front and to our south Sunday afternoon. Our
active weather pattern continues, with another round of
precipitation possible Tuesday (mainly over our far north and
eastern counties).
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 632 PM CDT Thu Aug 19 2021
Terminals KABR,KATY,KPIR,KMBG
Mostly VFR conditions are expected through the early morning
hours, but then after that lower clouds will move into the region,
but then should mix out some in the afternoon. Isolated to
scattered thunderstorms are expected through early Friday evening.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...TDK
SHORT TERM...Mohr
LONG TERM...KF
AVIATION...TDK
Area Forecast Discussion
National Weather Service Denver/Boulder CO
921 PM MDT Thu Aug 19 2021
.UPDATE...
Issued at 920 PM MDT Thu Aug 19 2021
There is some lingering convection going on in the mountains and
over the northern and northeastern border area of the plains. Some
of the models are continuing to show additional rainfall over,
the already soaked, eastern Phillips County. This area has
already experienced significant widespread flooding.
Some of the models are also continuing to show a line of showers
and storms come across the CWA overnight associated with the
upper trough axis passage.
&&
.SHORT TERM...(This afternoon through Friday)
Issued at 130 PM MDT Thu Aug 19 2021
Main concern through this evening remains the severe threat across
the northeast plains of Colorado this afternoon and evening, and
flash flood threat across the fire burn scars through this afternoon.
Severe thunderstorm watch has just been issued for much of the
northeast plains of Colorado through this evening.
Currently, unseasonably strong upper low spinning across far
northwest Utah with scattered showers and thunderstorms ongoing
across western Colorado. Thunderstorms now developing across our
mountains, mainly along and east of the Continental Divide and
across the foothills. Stronger storms are also developing further
east along some convergence across eastern Washington county.
Surface dewpoints holding in the 50s with some mid 60s across the
far plains Given latest model guidance, the best chance still
looks to be along and north of a line from Denver to Akron
including the far northeast corner as well which will be just
north and northeast of the surface low. Given dewpoints in the
60s, mixed layer CAPE values 1000-2000j/kg. Main threats will be
damaging winds up to 60 mph and hail up to 2 inch diameter hail.
Could even see a low tornado threat over the far northeast corner
through the evening with decent shear profile in place. Lesser
threats of severe weather further south across the Palmer Divide
to low level drying with the southwest flow.
Across the mountains and nearby plains the storms will have shifted
north and east by early evening with a rather quiet evening
expected. However the back of the trof approaches later tonight,
could see a line of showers and thunderstorms develop. Latest HRRR
showing this between 08-12z tonight through early Friday morning. As
the upper trof moves across, expect increasing subsident and drying
westerly flow. Cross sections show wind gusts up to 60 mph over
higher mountains and foothills for Friday morning. Expect decreasing
winds Friday afternoon as the trof moves further away from northern
Colorado. Temperatures will remain on the cooler side, with
readings mainly in the lower 80s across the plains.
.LONG TERM...(Friday night through Thursday)
Issued at 230 PM MDT Thu Aug 19 2021
Quieter weather can be expected for most of this period. We`ll
start off fairly dry across our forecast area with downslope flow
in place Friday evening. Winds will diminish in the early evening
hours with decreasing flow aloft and mixing. There is a small risk
we could see some weak convection over the Palmer Divide area
including Lincoln County overnight. Those shower/storm chances
would be due to weak mid level moisture convergence, but they
wouldn`t be much.
By Saturday, warm advection will occur in moderate southwest flow
aloft. This will result in breezy and somewhat warmer conditions.
We can`t rule out a couple late day showers/storms with just
enough destabilization and moisture returning in the southwest
flow aloft. Most of that chance would be over the mountains.
For Sunday through early next week, the ensembles point to a
continuation of somewhat drier but warm west/southwest flow aloft
over the forecast area. High temperatures will likely return to
the lower 90s for the lower elevations by Sunday, and remain in
place Monday and Tuesday.
There is fair ensemble agreement that we cool and moisten a little
toward next Wednesday, leading to a little higher chance of
storms over the forecast area by the middle part of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 916 PM MDT Thu Aug 19 2021
Will go with some weak drainage winds at DIA kicking in around 05
or 06Z. Before 12Z, the upper trough axis is supposed push across
with west and northwesterly winds at the airport after that.
There could be some convection associated with the upper trough
axis around 12Z as well so left the "VCTS" in the TAF.
&&
.HYDROLOGY...
Issued at 130 PM MDT Thu Aug 19 2021
There is the increasing threat of flash flooding over the burn
scars this afternoon, especially across Cameron Peak and Calwood
burn scars with more moisture and heating resulting in higher
instability. Could see a quick 1/2 to 3/4 of an inch of rain in 30
minutes or less with the stronger storms. The storm motions will
be moving quite fast but given he moisture and strength it won`t
take much to result in a situation. Have increased our flash flood
threat to the elevated category today for Cameron Peak and
Calwood with a slightly lesser threat over Williams Fork and East
Troublesome. Also could be a flood threat across the far northeast
plains with strong to severe storms given the pw values through
this evening.
Friday through Monday will be mostly dry with no flash flood
threat. A couple weak showers and thunderstorms will be possible
Saturday into early next week. However, moisture will be limited
with little rainfall expected with this activity.
There could be a limited flash flood threat developing for the
burn scars toward Wednesday if some monsoon moisture returns to
the region. There seems to be reasonable agreement of this
increase in moisture per model ensemble guidance.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE.......RJK
SHORT TERM...Entrekin
LONG TERM....Barjenbruch
AVIATION.....RJK
HYDROLOGY....Entrekin
Area Forecast Discussion
National Weather Service Cheyenne WY
507 PM MDT Thu Aug 19 2021
.SHORT TERM...(This evening through Friday)
Issued at 206 PM MDT Thu Aug 19 2021
Severe weather remains the primary forecast challenge in the
short term period, although in a slightly tempered state. An
outflow boundary/subsidence region passed through much of
southeastern Wyoming this morning, and has moved out into the far
western counties of Nebraska early this afternoon. This boundary
was evident on satellite imagery and on surface observations. This
boundary has caused a rather notable shift in surface flow, which
is still mostly northerly to even northwesterly at most SE WY
sites as of 20z. The net effect of this mesoscale boundary has
been to greatly reduce wind shear/low-level hodograph size as well
as stabilize the atmosphere over much of southeast Wyoming and
western Nebraska. This will ultimately limit the thunderstorm
threat for much of the day today. The one exception will be in
Cheyenne and Morrill counties in western Nebraska, which remain on
the warm/unstable side of the boundary. Thunderstorms near severe
limits were already in progress here as of 20z, and are expected
to continue eastward through the day. As the afternoon progresses,
additional thunderstorm development is likely to the south of the
Wyoming border. However, given the passage of the aforementioned
boundary, there is considerable doubt as to whether any severe-
level convection will survive north of Weld county in
Wyoming/Nebraska in the currently stabilized atmosphere.
Farther north and west over Wyoming and western Nebraska, expect
bands of elevated shower and thunderstorm activity to last through
the afternoon and evening hours as our potent trough moves
through. Briefly gusty winds over 40 mph remain possible, as well
as heavy downpours. The flooding threat also appears rather
tempered for today, given both the stabilizing effects of the
morning boundary as well as notably speedy storm motions of near
30 knots.
Overnight, most CAM guidance indicates that most shower and
thunderstorm activity will come to an end by around 10pm. The one
exception is the HRRR, which develops an additional band of
showers and possibly thunder around 8z. This activity is likely a
result of the actual trough/frontal passage, so will have to keep
an eye out for development after midnight. Freezing levels are
still expected to drop below 11,000` overnight, and with bit of
moisture lingering to the west, a dusting of snow remains in the
forecast for the highest elevations of the Snowy and Sierra Madre
ranges.
A much drier, cooler day is in the forecast for Friday. Isolated
showers and possibly a rumble of thunder or two are possible over
the higher terrain of the Laramie range, however areal coverage
will be extremely limited as nearly all low-level moisture will be
eradicated by this timeframe. Temperatures will run 5 to nearly 10
degrees below average - a very early fall preview will be in the
air.
.LONG TERM...(Saturday through Wednesday)
Issued at 305 AM MDT Thu Aug 19 2021
Long range models continue to show generally drier and quiet
weather across southeast Wyoming and western Nebraska this weekend
through the middle of next week. A few weak shortwave troughs, embedded
in the near-zonal/weak southwest flow aloft, will push east across
the region. Other than enhancing some thunderstorm activity, not
much is expected from these systems. Temperatures will remain on
the cool side Saturday, especially in the morning, with early
morning lows in the 40s and some mid to upper 30s in the cooler
valleys west of the Laramie Range and I-25 corridor. Highs on
Saturday will be about 5 to 10 degrees warmer compared to Friday
with afternoon temperatures in the mid 70s to low 80s. Models show
the first upper level trough rapidly moving east across Montana
and Wyoming. Due to it`s progressive nature, low level moisture
won`t be able to return to a significant part of the high plains,
so kept POP on the low side for now with the best chance for some
isolated/widely scattered thunder showers in the mountains and
across central Wyoming. Daytime temperatures are expected to
slowly increase Sunday and Monday as 500mb heights increase
towards 590dm. Highs in the mid 80s to mid 90s are expected to
return to most of the area by Monday. It will be windy during the
weekend with gusts up to 45 mph possible across most of southeast
Wyoming, especially in and near the Wind Prone areas. The best
midlevel gradient shift northward into early next week, so winds
do not appear as strong as a few days ago. For later in the week,
models are starting to show the return of some Monsoon moisture to
the Front Range by Wednesday and Thursday next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 503 PM MDT Thu Aug 19 2021
Thunderstorms this afternoon are on the wane as strongest storms
now moving into central Nebraska. There is a chance of low clouds
and fog out in the Nebraska panhandle this evening...impacting
KSNY and KAIA. HRRR hinting at IFR conditions developing out there
around 05Z to 06Z. Winds still expected to be on the increase as
upper trough moves through southeast Wyoming overnight into Friday
morning. So will continue the strong winds at most TAF sites
through the afternoon Friday.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from midnight tonight to noon MDT Friday for
WYZ110-116-117.
NE...None.
&&
$$
SHORT TERM...MAC
LONG TERM...TJT
AVIATION...GCC
Area Forecast Discussion
National Weather Service Duluth MN
654 PM CDT Thu Aug 19 2021
.DISCUSSION...(This evening through Wednesday)
Issued at 409 PM CDT Thu Aug 19 2021
Near-critical fire weather conditions will continue into early
evening and will occur in spots again Friday. Severe thunderstorms
will also be possible later Friday into Friday night with breezy
conditions and cooler temperatures for Saturday.
Tonight will be mostly clear and mild with lows only dropping to
60 to 70 degrees. Most areas will will remain dry on Friday with
breezy southerly winds expected to gust from 20 to 30 mph.
Humidity values will be a bit higher than today, mostly between 35
and 50 percent, but given the state of the fuels and wind gusts
near-critical fire weather conditions are expected.
The models are in decent agreement that a weak shortwave will
precede the main upper wave on Friday and it may set off some
showers and thunderstorms over about the western third/half of the
Northland as early as late morning. We followed closer to the RAP
for instability and shear as the GFS is suffering from having too
much dry air in the low levels. The GFS was showing dewpoints
dropping into the mid 50s this afternoon at KBRD and that is
around 8 degrees lower than their current value. The RAP is doing
better with low level moisture this afternoon and we feel it
better forecasts the moisture on Friday. MLCAPE values per the RAP
will rise to 1000-1700 j/kg over our far west by late afternoon
with deep layer shear at or below 25 knots. The risk for severe
through mid afternoon will be relatively low with the risk
increasing late afternoon into the evening as the southerly low
level jet increases to 40 to 45 knots. Forcing will increase
during the late afternoon and evening as the main upper wave moves
through the Northern Plains kicking the cold front east. PWAT
values will rise to 1.7 to 2 inches so plenty of moisture will be
present. Deep layer shear will increase to 30-40 knots as the
upper wave nears the area and with the increasing low level jet.
Instability will decrease from west to east across the Northland
though with highest values occurring during the evening and over
western areas. The strength in the forcing will make up some though
for the lack of instability further east. We expect storm mode to
transition rather quickly to a line or clusters of storms given
the strength of the forcing. The main hazard will be damaging wind
due in part to storm mode but also mid-level lapse rates are not
very impressive. The best chance for large hail will be early in
the storm development Friday evening with any discreet storms.
Although not high, there is a chance for a tornado given low level
hodographs and the shear provided by the low level jet. The 0-3km
shear vector is southerly reducing the chances for QLCS tornadoes
given the line of storms should move west to east. However, the
shear strengthens quite a bit during the evening with adequate
shear developing for northeast moving line segments. This of
course assumes a strong enough line of storms maintains well into
the evening. Storms will decrease from southwest to northeast
late Friday evening into Saturday morning. Rainfall amounts will
range from only a tenth to quarter inch over the Arrowhead to a
half to near 1.5 inches over our far western area closer to the
stronger forcing and better instability. Locally higher amounts
will occur with any training storms given the high PWAT values.
A chance for showers and a few thunderstorms will linger into
Saturday but decrease from south to north. It will be a much
cooler day with lower dewpoints. Highs will range from the mid
sixties to mid seventies and winds will be breezy from the west to
northwest.
Another stronger area of low pressure will pass north of the
Northland Sunday night and will bring chances for shower and
storms to the region. Significant rainfall is unlikely with this
system
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 654 PM CDT Thu Aug 19 2021
Winds and diurnal cumulus will continue to diminish, leading to
quiet conditions overall tonight. The only exception will be at
HIB as there is the potential for another night of MVFR/IFR
visibility reductions due to fog. Much of the day Friday will be
VFR, with another round of SCT to BKN diurnal cumulus clouds.
There will be some gusty southerly winds, with widespread gusts
to around 20 to 30 knots possible. Increasing chances of showers
and thunderstorms are expected in the late afternoon/evening
hours Friday as a trough of low pressure moves into the region. At
this time, precise timing of this activity is a bit uncertain, so
we largely kept it out of the TAFs for now, except for a VCTS
mention for BRD, which should see this activity before the other
TAF terminals. These chances of showers and storms will expand
eastward through the evening and overnight hours Friday.
&&
.MARINE...
Issued at 409 PM CDT Thu Aug 19 2021
Winds will be less at or less than 15 knots tonight into Friday
with waves 2 feet or less. There will be some fog over the lake
due to high dewpoints over the lake and onshore wind in spots. A
strong cold front will move through the area late Friday night
into Saturday morning. Thunderstorms will be possible with the
front Friday night into Saturday morning. A few strong storms will
be possible. Southerly winds will increase Friday night then
increase further on Saturday out of the west. A few gusts around
20 knots will occur Friday night with strong gusts of 20 to 25
knots on Saturday. Conditions will become hazardous for small
craft on Saturday and Small Craft Advisories may be needed for
most of the nearshore waters.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 67 86 63 72 / 0 10 70 20
INL 69 89 58 67 / 0 60 80 60
BRD 68 86 60 70 / 10 70 90 10
HYR 62 86 63 75 / 0 10 80 30
ASX 65 90 66 79 / 0 10 60 40
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&
$$
DISCUSSION...Melde
AVIATION...JTS
MARINE...Melde
Area Forecast Discussion
National Weather Service Des Moines IA
657 PM CDT Thu Aug 19 2021
...Updated for 00Z Aviation...
.DISCUSSION.../Tonight through Thursday/
Issued at 332 PM CDT Thu Aug 19 2021
Forecast Highlights:
-- Warm and humid through Friday
-- Strong to severe storms toward and after 6pm Friday in our
forecast area
-- More seasonable, drier on Saturday
-- Strong to severe storms possible later Sunday/Sunday night
-- Additional storm chances and hot and humid through early next week
Details: Typical mid-August weather is ongoing this afternoon with
warm and humid conditions across the state. Diurnal cumulus have
once again developed and are widespread on visible satellite, which
has been the status quo this week. Yesterday, a few showers tried to
bubble up over far southern Iowa and convective allowing models
(CAMs) are once again attempting to generate isolated showers or
storms this afternoon over southwestern Iowa. The WRF-ARW and NAM
Nest have been the proponents of showing convection through this
week with the RAP giving some indications yesterday and the HRRR
today. Cumulus clouds may try to grow vertically, but will largely
be limited by higher mid-level heights as the ridge has moved over
the region today. At this point, any development has been focused
over southwestern Iowa over the next few hours with low PoPs.
Attention will then focus on the big trough that is currently dug in
over the Intermountain West. GOES-East upper level water vapor
imagery shows the cyclonic spin near Salt Lake City with derived
motion winds showing a near 100 knot jet beginning to round the base
of the trough. As this trough crests the Rockies tonight and moves
northeastward into the Dakotas on Friday, it will take on a negative
tilt with surface low pressure over the Dakotas and east of the
Colorado Rockies. There may be some elevated, diminishing convection
that may reach western Iowa toward daybreak Friday. There is
uncertainty on how far east this will make it and whether it will
even survive into western Iowa. CAMs including the 12z HREF are
largely muted with perhaps a CAM solution or two showing isolated
storms making it into our western forecast area. With a majority of
current guidance showing a drier solution and in coordination with
western neighbors, have gone with a dry forecast tomorrow morning.
Certainly, the more likely period of storms will be as the front
arrives into the state late in the afternoon. Initially, the
stronger surface low will be the one over Colorado, but as that
moves towards Iowa later Friday it will weaken and be along the cold
front that will extend from the strengthening low over the eastern
Dakotas. Well in advance of the front, it will be warm and humid
with diurnal cumulus likely developing again per 12z HREF cloud
cover. These clouds are not expected to have much vertical depth as
the NAM and GFS forecast soundings show warm, capping layer aloft,
which will weaken in the afternoon. If any storms were to form in
the warm sector, which is not likely, it would have a very weak
shear environment -- weaker than what has been forecast the past two
days for Friday. SBCAPE will blossom in the sultry airmass with
deterministic models and the 12z HREF having values ranging from
1500 to 2500 to 3000 J/kg ahead of the front over western Iowa. The
highest deep layer shear continues to be in the vicinity of the front
and that is where low level lapse rates will be around 9C/km. The
low level wind field from the southeast will also increase to 15 to
30 knots, especially as the front nears western Iowa in the
afternoon, and this will increase the 0-1km SRH and elongate the
lower portion of the hodograph a bit. CAM guidance show perhaps a
brief period of discrete supercells, which is supported by 30 to
maybe near 40 knots of 0-6km shear with vectors orthogonal to the
front. However, there is fairly good agreement among the 12z CAMs
that storms will form into a line along the front. 0-3km bulk shear
vectors are perpendicular to the front and may top 30 knots for a
QLCS tornado potential over southwestern Iowa if the line can
maintain cold pool balance late in the afternoon and early in the
evening. It should be noted that the recent 18z HRRR is weaker,
perhaps slightly slower, and more of a broken line of convection.
Any tornado threat will be early in event with discrete storms that
are able to maintain in the deep layer shear environment and perhaps
attain deviant motion. Storm hazards will also include hail given
sufficient -10C to -30C CAPE and storm mode. Damaging wind gusts may
also occur with soundings showing dry mid-level air that could be
entrained in downdrafts. While the tornado threat will end fairly
quickly, hail and more so strong, gusty winds will continue after
dark. With instability dropping to around or under 1000 J/kg by 4 or
5z, severe risk should be waning as storms move into central Iowa/I-
35 corridor. All storms are expected to be east of our forecast area
by daybreak Saturday.
While precipitable water values will be around 2 inches along
the front, 850-300mb flow will be cross boundary and the front will
be progressive. The 12z HREF localized probability matched mean
shows very isolated values of 4+" and a few members of the 12z GEFS
showing greater than 2 inches in 6 hours. However, these are the
minority showing any flash flooding concerns with the 12z
deterministic synoptic and mesoscale models and 6z ensemble members
showing little in the way of exceeding 6 hour flash flood guidance,
which is 3.75" at a minimum. With the antecedent dry conditions,
storms would have to align just right over an urban area to realize
any water issues.
As the trough lifts away from the area on Saturday, cooler and drier
air will move over the region. Afternoon temperatures will be 5 to
10 degrees lower over the state with middle 70s over northern Iowa
and low 80s over southern Iowa. Temperatures and dewpoints will
begin to tick upward on Sunday as strong theta-e advection prevails.
As another trough moves over the northern states later Sunday, a
ribbon of 2000 J/kg SBCAPE will be ahead of a front that will be
west of Iowa. The deep layer shear is certainly higher over 40 knots
and will support strong to severe storms developing over eastern
South Dakota or eastern Nebraska. Those storms will move into Iowa
late in the day into Sunday night and could pose a risk for at least
hail and strong, gusty winds.
An active pattern will remain into next week as the mid-level ridge
builds over the southern US and tries to bring its influence to
southern Iowa. With Iowa on the northern periphery of the ridge, weak
shortwave impulses will be able to move over the state. The stronger
trough mentioned in previous discussions looks to remain farther
north over the southern Canadian prairies leaving more nebulous
shortwaves over our region. Further, the front that will be the
focus for storms on Sunday may linger in a weakening fashion over
the state providing varying degrees of surface convergence through
mid-week. Thus, this will keep low PoPs in the forecast with the
typical expectation that storm chances will probably be highest
later in the day into the overnight hours with a minimum in the
morning hours.
&&
.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 643 PM CDT Thu Aug 19 2021
VFR conditions expected this evening and overnight. Some lingering
cumulus remain with FEW/SCT bases around FL040 to FL050. Winds
will decrease to under 10 knots from the south to southeast this
evening into the overnight hours, but will pick up again ahead of
a boundary late morning Friday. Storms are likely after 21Z Friday
and mentions will have to be added in future issuances.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Ansorge
AVIATION...KCM
Area Forecast Discussion
National Weather Service Grand Forks ND
1038 PM CDT Thu Aug 19 2021
.UPDATE...
Issued at 1037 PM CDT Thu Aug 19 2021
Weakening isolated showers/thunderstorms continue to move north
in far northwest MN, with another weak shower moving into the
Devils Lake Basin. Cluster of thunderstorms further west is
drifting north and based on trends. Latest short range CAMs
indicated less activity during the overnight period (though there
is still run to run variance). There is still good consensus that
a series of shower/thunderstorm clusters and scattered activity
between these features eventually spreads west to east Friday
morning. I made minor adjustments to the overnight/morning period.
UPDATE Issued at 654 PM CDT Thu Aug 19 2021
Isolated weak showers and thunderstorms have developed along
convergence zone orientation southwest to northeast, and
continues to show little in the way of persistence (tending to
pulse). This matches trends shown by HRRR and adjustments made
during afternoon forecast update. I made further adjustments to
reflect the coverage duration, as this may linger even after
sunset. SPC objective analysis shows ML CAPE axis 1000-2000 J/KG
along this convergence zone, however due to highly elevated nature
of parcels/skinny elevated CAPE profiles, very little shear, and
very warm air mass (freezing levels over 15 kft AGL) these pulsy
updrafts should not become severe this evening.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 342 PM CDT Thu Aug 19 2021
Challenge for the short term will be increasing rain chances and
precip coverage, severe weather potential and heavy rain threat
Friday and Friday night as we see a pattern change from the hot
and dry weather of late.
This evening went ahead and added the slight chance for a
thunderstorm along the SFC boundary in the central valley and into
NW MN. The combination of instability and forcing from the mid
level boundary lifting back to the north. CAMs do indicate a few
small isolated pockets of activity developing within the area for
a few hours.
Synoptically a negatively tilted trough will lift NE from the
Rockies overnight tonight with lead impulse causing a round of
showers and thunderstorms developing across the SD and Nebraska
high plains this evening. This activity may spread into the
Devils Lake basin after midnight and before sunrise. With model
consensus closing and lifting the 500mb low across central ND and
into southern Manitoba tomorrow there is high confidence in
significant rainfall as PWATs climb above 2 inches within the warm
sector ahead of the SFC low. Best chance for an inch or more of
precip will be along the track of the upper low which currently
appears to be across the Devils Lake basin and into the northern
valley. Other areas will receive more than an inch however
coverage will be more spotty as is the nature of convective
activity. With that said there is the potential for some training
storms and possible flash flooding even with the extremely dry
conditions as tropical rainfall rates develop as convection
realizes the 2+" of PWAT and storms produce a quick 1 to 2 inches
in 30min or less. Based on the 12Z HREF localized probability matched
mean some pockets of 3 to 4 inches are possible with the max from
the ensemble showing 5+ inches. Something to watch and could be
possible given the NAEFS mean PWAT for 00Z is at MAX or higher
than all climatology for the end of Aug.
Also of concern will be the potential for severe storms to
develop along the cold front/dry line tomorrow afternoon and
evening as it surges east impacting the Red River Valley and NW
and west central MN. All storm modes and severe threats are
possible initially with a linear mode and wind the primary concern
expected to develop as storms move into Minnesota though with
embedded supercellular potential continuing based on shear values,
tornadoes remain possible within the QLCS. Will see activity
ending west to east with storms ending in the east around
midnight.
.LONG TERM...(Saturday through Thursday)
Issued at 342 PM CDT Thu Aug 19 2021
The active pattern continues through the long term period. Multiple
shortwaves will come through the area, bringing chances for shower
and thunderstorm chances back. A condition severe weather risk does
appear possible on Sunday, although a lot of details need to be
ascertained before messaging specifics. Temperatures will also
maintain in the 60s and 70s for much of the long term period with
lows falling into the 40s and 50s.
SUNDAY...The first system expected to impact the area comes Sunday.
Another shortwave will move through the area with meaningful
moisture transport associated with it as southerly flow returns to
the area. Moisture content is not going to be near as high as it is
right now, although PWAT anomalies are approaching 1 standard
deviation amongst ensemble members and NAEFS/ECMWF R-Climate
percentiles are in the 90th percentile. Instability with this system
isn`t too terrible, as a plume of 7 K/km lapse rates advect with the
system into the open warm sector, lending credence to the potential
for some severe weather. Where things draw some concern is with this
system, there appears to be a solid probability for strong flow
within the 850-500mb layers. Looking at R-climate, meridional flow
is approaching 97.5th to 99.5th percentiles, indicating rather
strong flow being forecast by ensembles. With ample low level flow,
shear profiles do look rather impressive compared to what they have
been, with 0-6km shear approaching above 50 knots and veered
hodograph profiles. Complicating matters is antecedent
shower/thunderstorm activity during the daytime, inhibiting low
level destabilization. While not too terribly outside the range of
possible outcomes, it does appear feasible that within the
reasonable range of outcomes that severe weather is a possibility
for Sunday, with the potential for supercells given the shear
profile. This is highly conditional, however, as near surface
destabilization will likely play a role in how Sunday plays out.
With the most likely outcome, it appears showers and storms will be
possible once again on Sunday, bringing the chance for more
showers and storms, bringing much needed rain to the area.
TUESDAY...Tuesday looks to bring another system through the area,
although ensembles have a little less of a handle on this than
Sunday. For the most part, positioning of this system appears to be
further north, so the highest chances for further precipitation will
be further north closer to the international border. Still, adequate
forcing does appear to make it down as a cold front sweeps through,
so precipitation is possible along the front within the area.
REST OF THE PERIOD...Ensemble guidance keeps us in this
southwesterly flow pattern through the end of the period. This will
lock us in the 60s and 70s for afternoon high temperatures, but also
keep precipitation activity up.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 654 PM CDT Thu Aug 19 2021
Isolated showers and thunderstorms have developed over parts of
eastern ND and northwest MN, however current trends/coverage only
indicate this may move within the vicinity of KTVF and not other
terminals this evening (will monitor). Better shower/thunderstorm
chances arrive after 09Z tonight in central ND and spread east by
midday Friday across eastern ND and northwest MN. Severe
thunderstorms and heavy rainfall become possible Friday afternoon
and evening. Gusty winds should diminish this evening, however
directions may be more variable as a front moves back and forth
tonight in northeast ND and far northwest MN.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...DJR
SHORT TERM...JK
LONG TERM...Perroux
AVIATION...DJR
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
641 PM CDT Thu Aug 19 2021
...AVIATION UPDATE...
.DISCUSSION...(This evening through Thursday)
Issued at 420 PM CDT Thu Aug 19 2021
Summary...
Showers and thunderstorms will be possible late tonight and into
Friday with a cold front. Some strong to severe thunderstorms
can`t be ruled out, but it appears the timing of this system will
keep best chances west of the area tonight, then east of the area
on Friday. Expect a one day cool down and drier air for Saturday
before warm/hot conditions return for Sunday and continue through
early next week. A weak cold front will bring chance for
thunderstorms (possibly severe) Sunday afternoon and evening. A
stronger cold front may arrive toward middle of next week and
provide additional rain chances.
Analysis...morning stratus lifted and transitioned to scattered
CU early this afternoon. There`s been some spotty showers mainly
along and E of Hwy 281, with latest GOES-16 1-min data showing
greatest concentration of agitated CU closer to Hwy 81. Tstms have
blossomed over NE CO and W NE within past couple of hrs. This
activity currently has more N than E movement attm, which will
probably keep activity W of the area thru the eve hrs. This
activity is in response to lead shortwave that proceeds a closed
upper low spinning near SLC. Despite the AM clds, temps have
warmed into mid 80s - low 90s. A brzy S wind is providing some
relief from the upper 60s - low 70s Tds.
Forecast Details...
The greatest concern in the short term will be tstm trends over
the next 24hrs or so. No real surprises with the current activity
developing W of the area, however model guidance is still split
on how it evolves later on tonight. Last several HRRR runs have
come in much further S, closer to Hwy 6/I-80, whereas most other
guidance either weakens activity as it moves in, or keeps it
mainly N/NW of the area altogether. Have been reluctant to
completely buy-in to this HRRR trend given lack of support from
other models, but it appears the diffs stem from LLJ orientation
and placement, as well as ability for MCS to develop a cold pool.
The later is something that the HRRR typically resolves
better...so it`s definitely worth considering and something to
keep an eye on. For now, kept likely PoPs across far W/N portions
of CWA (from around LXN to ODX), with 30-40 PoPs as far S as Hwy
6. If HRRR model trends continue this eve, and convection in SW
Neb. is able to turn more E and grab the nose of the LLJ, the
natural veering of the LLJ would likely steer activity further
S...in which PoPs for Tri Cities would need to be raised. Given
the somewhat outlier solution, will let eve shift re-evaluate and
adjust as needed. As for severe potential...still looks like
timing favors mainly near and after midnight for arrival into W
zones. Think this would tend to limit wind potential to mainly
Dawson or Valley Counties. Can`t rule out some marginally severe
hail pretty much any time thru Fri AM as LLJ will help pump up to
2500 J/kg of MUCAPE into the area, and effective deep layer shear
remains around 25kt. Lapse rates are not great, though. Finally,
while I don`t think this will be a big issue, could see some
locally heavy rain amounts if HRRR solution verifies. PWATs will
incr to near 1.75", and deep layer flow relative to nose of LLJ
could foster at least modest training in localized areas. Again
though, this appears to be the outlier solution. Activity should
gradually weaken Fri AM as LLJ weakens.
In general, models have trended towards a stronger and more
northern sfc low pressure, which results in a more progressive
cold front timing on Fri. This could very well keep the primary
tstm development zone Fri aftn/eve to the E/SE of the forecast
area. In fact, latest HRRR/NAMNest slide the front thru SE zones
by 21-22Z, w/ Wrly flow ushering in much drier air. Have decr PoPs
during this time, and perhaps not enough. Even the traditionally
slower EC keeps activity just SE of a Beloit to HJH line.
Pleasantly cooler and drier conditions should settle in for Friday
night and Saturday. Temps in the upper 70s to 80s, Tds largely in
the 50s, and a gentle N breeze should make for a nearly perfect
August day. This is temporary, however, as warm/hot conditions
return in earnest Sun ahead of another cold front associated with
a shortwave tracking from Rockies into N Plains. Models suggest a
low end chc for shwrs/storms early Sun associated with veering
LLJ, but better chcs could come from weak cold front trailing from
ND sfc low pressure. Still not sold we`ll see convection this far
SW given H7 temps 12-13C, track of primary shortwave N of the area
across the Dakotas, and neutral or slight height rises. If we do,
however, looks like we`ll have plenty of instability and perhaps
even some shear due to proximity to S fringes of mid level jet
streak. Best chcs look to be over NE corner of CWA.
Hot and mainly dry conditions are expected for Mon-Tue as weak
cold front from Sun PM washes out and lifts N. Ensembles appear to
be in pretty good agreement for fairly widespread 90s each day,
perhaps even low 100s across KS zones. Another, possibly stronger,
cold front looks to arrive sometime middle of next week.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 637 PM CDT Thu Aug 19 2021
Two main concerns for this forecast, potential thunderstorms
overnight and possibly yet another low stratus deck in the morning
hours. To address the first point, storms are currently forming
off to the west of the outlook area and will continue into the
overnight hours and work their way eastward and could affect the
terminals mainly after local midnight. As for the second point,
the last two mornings have seen an IFR and even LIFR stratus deck
that has moved in around dawn and lasted for several hours.
Depending on the influence of convection in the area, this could
very well be the case again in the morning. These are both
things to keep an eye on for changes and refinement in future
updates.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
DISCUSSION...Thies
AVIATION...Shawkey
Area Forecast Discussion
National Weather Service Gray ME
1140 PM EDT Thu Aug 19 2021
.SYNOPSIS...
Low pressure of tropical origins will move northeastwards
tonight before approaching Nova Scotia by Friday afternoon.
Tropical downpours will end by late this evening with Canadian
high pressure building in on Friday through Saturday with mostly
dry weather expected. Tropical Cyclone Henri may very well
approach eastern New England on Sunday or Monday.
&&
.NEAR TERM /TONIGHT/...
1140 PM Update... Performed one last round of tweaks to T/Td
and Sky/PoP/Wx for the overnight period but overall the
forecast is in good shape. Bumped up overcast skies through the
overnight and blended in more hires model input in PoPs.
Otherwise am expecting widely scattered showers with the soupy
atmosphere leading to patchy fog over most of the area.
945 PM Update... Dropped the remainder of the Flash Flood Watch
this evening with weaker and more scattered rainfall being
observed at this hour.
715 PM Update...
Primary change for now was to remove thunder from the forecast
through tonight as I see no cloud pulse activity over the region
at this hour... also boosted fog a bit overnight with reduced
visibilities already being observed at this hour. Otherwise, am
looking for stratiform rain to continue to slide Downeast in the
coming couple hours with more scattered activity near the
parent circulation through the overnight before pulling away in
the morning. Have kept the remaining flash flood watch up for
now as another steadier batch of rain is set to track through
there this evening, although am not particularly worried since
we underperformed a bit with initial totals with the stratiform
swath earlier today.
Previously...
Low pressure from what was once Tropical Storm Fred is
currently located near Western Massachusetts with tropical
downpours pivoting around much of New England. The steadiest of
the initial rain band has now moved out of New Hampshire but
wrap around convective showers and isolated thunderstorms
remain. Further to the north, steady moderate rain continues to
fall from roughly Lewiston up towards Waterville Maine. This
band will continue to move northeastward before exiting our area
by around 9 pm. So far observed rainfall amounts have been a
bit lower than expected despite impressive rainfall amounts
across portions of southern New England in excess of 5 inches.
That area of rain largely missed us to the south with our area
mostly just experiencing a soaking moderate to at times heavy
rain with up to around 1 inch of accumulation. Based on the
latest radar trends and near term forecast guidance the Flash
Flood Watch was cancelled for New Hampshire but decided to keep
it in place for now across Maine. Some guidance such as the HRRR
sill indicates that up to another inch of rain is still
possible in Maine, which could potentially result in some
additional flooding depending on how quickly it falls. Rain will
end from southwest to northeast later this evening but it may
linger a little longer up towards the Mid- Coast.
&&
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
Some lingering showers or light rain may still be present
across portions of the Mid-Coast early on Friday morning but the
rain should largely be gone by daybreak. Skies will become
partly cloudy and depending on how much sun we experience it
could be quite warm with high temperatures into the 80s and
surface dewpoints into the upper 60s to lower 70s. Other than an
isolated afternoon shower it will be a much drier day as
northwest winds bring in slightly drier air from the north.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
The concern in the long term is obviously what will Henri do. We
are following NHC guidance for the going forecast which
possibly brings Henri to eastern MA as a weak hurricane or
strong TS later Sunday. However, do realize that there is
considerable inherent forecast track error at this time range.
At this time, no watches will be issued for the Maine/NH coastal
waters due to the long time any potential impacts could arrive
(if they do at all). At the least, we should see increasing
winds and seas by later Sunday or Sunday night on the coastal
waters. With relatively high astronomical tides in place this
could pose a splash-over/minor coastal flooding issue from
Portland on south to the Seacoast. We will continue to monitor
trends at this time. For the time being, continue to monitor NHC
forecasts.
&&
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Short Term...
IFR/LIFR conditions expected tonight as rain ends but fog
develops, especially across valley terminals. Fog will lift by
around 13Z on Friday with VFR conditions returning through
Friday night.
Long Term...Mainly VFR with showers possible Saturday into
Sunday. Possible effects from Henri could arrive late Sunday
into Monday but high uncertainty remains.
&&
.MARINE...
Short Term...
Southeast winds may approach 25 kts with seas around 3 to 4 feet
for a few hours this evening as low pressure passes to our west.
Light northwest winds return tomorrow as weak high pressure
moves in.
Long Term...Will continue to sub-SCA conditions through much of
Saturday night with SCA winds and and seas developing Sunday.
Continue to monitor latest NHC forecast for details about Henri.
It`s possible that tropical storm conditions will occur Sunday
into Monday.
&&
.HYDROLOGY...
The Flash Flood Watch has been cancelled with steady rains
exiting to the east and widely scattered showers remaining
overhead as the main circulation crosses. Looking at rainfall
totals across the region, around 1 to 2 inches of rain fell with
locally higher amounts near 3 inches observed in portions of
southern New Hampshire. A glance at rivers shows modest rises
with forecast crests well below flood stage in the coming day or
so.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.
&&
$$
UPDATE...Casey
NEAR TERM...Tubbs
SHORT TERM...Tubbs
LONG TERM...Ekster
Area Forecast Discussion
National Weather Service Huntsville AL
1101 PM CDT Thu Aug 19 2021
.UPDATE...
For 06Z TAFS.
&&
.NEAR TERM...(Tonight)
Issued at 923 PM CDT Thu Aug 19 2021
In comparison to a few hours ago, convection has weakened
significantly in coverage/intensity across the Tennessee Valley. The
"heaviest" activity as of 9 PM was moving to the ESE around 10 mph
from east of Huntsville to NW Georgia while on a dissipating trend.
Other activity, also on a weakening trend covered an area from south
of Jackson TN to across central Mississippi and west/central Alabama.
The water vapor views indicated somewhat drier air filtering in
across the region from the NW. The fog/low cloud view and a few
observations to our west indicated low clouds forming in those mostly
clear areas.
Latest output from the HRRR were in agreement with the activity
remaining on a weakening trend into the late night. The RAP/FV-3, and
more the NAM, however indicated shower activity returning towards
daybreak Friday morning, with more numerous coverage in the later
morning and afternoon. Given the presence of showers to our west,
will keep lower end shower/thunderstorm chances in for the late
night. Between the showers, with generally clear skies and light
winds, will maintain patchy fog as well. The on-going forecast looks
to be in fine shape. Only a few tweaks that should not change big
picture wording will be made soon.
.SHORT TERM...(Friday through Saturday night)
Issued at 203 PM CDT Thu Aug 19 2021
Active weather will continue for both Friday and Saturday across the
CWFA as we transition into a NW flow pattern thanks to an upper high
building/strengthening across E/SE TX. This should set the stage for
any disturbances to ride up and over this feature, impacting the TN
Valley both tomorrow/Saturday.
Like the midnight shift alluded to, in such a tropical airmass, heavy
rainfall and any resultant flash flooding will continue to be the
primary concern during this time. Second to that will be any gusty
winds from strong to marginally severe storms that develop.
The questions during this time is in what fashion the storms come
marching down into the CWFA. The devil is definitely in the details
with this setup, as NW flow in the TN Valley is never an easy
forecast. Whether we`ll have an MCS marching across the area
tomorrow night, or a lesser organized round of storms is yet to be
determined, but stay weather aware the next day or two for the
potential for flash flooding or 40-50mph winds.
As a result of the increased convection around the area
Friday/Saturday, daytime highs will top out in the middle 80s.
.LONG TERM...(Sunday through Wednesday)
Issued at 203 PM CDT Thu Aug 19 2021
The upper ridge over TX will strengthen and expand Ewrd as we head
into Sunday, which will drastically reduce the chances for showers
and storms on Sunday/Monday. As a result, though, temperatures will
warm into the middle 90s. Add to that the abundance of low level
moisture thanks to recent rains, and heat index values begin to creep
up as well during the start to the new work week. HI values in the
low 100s will return, but should stay below advisory criteria (105F).
Eventually, the high begins to break down, and with this comes the
return of daily chances for showers and storms beginning Tuesday,
and increasing by Wednesday and beyond.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1101 PM CDT Thu Aug 19 2021
Shower redevelopment is possible in the late night, as weak upper
level support approach from the west. Otherwise light variable winds
and residual moisture from recent rainfall could be conducive for
the development of fog before sunrise Fri. Daytime heating of a very
moist atmosphere will produce scattered to numerous showers and
thunderstorms mainly in the afternoon. Gusty erratic winds, reduced
CIG/VSBY from locally heavy rain could impact the terminals in the
afternoon. Shower activity should wind down in the evening. Although
some guidance has reduced CIGs Fri evening, have held on to VFR
conditions, and let later model output resolve this potential.
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&
$$
NEAR TERM...RSB
SHORT TERM...12
LONG TERM...12
AVIATION...RSB
For more information please visit our website at
weather.gov/huntsville.
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
954 PM EDT Thu Aug 19 2021
.SYNOPSIS...
Isolated showers will linger into this evening as widespread
rain moves east. Partly cloudy skies and fog are expected
tonight. The threat for showers and thunderstorms is forecast
to diminish Friday under weak high pressure. A couple of
disturbances will interact with an unstable airmass to keep a
low chance for precipitation through the weekend.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As the few remaining showers around the area continue to
dissipate, the main concern tonight is fog potential. A Dense
Fog Advisory is already in effect for the southern two tiers of
ILN counties.
With the center of a broad surface high over the area, winds
have gone mostly calm. With a gradual reduction in cloud cover,
most of the forecast area should be clear to mostly clear
overnight as well. Dewpoints remain in the upper 60s to lower
70s, with temperatures only in the lower to mid 70s, suggesting
that temperatures may easily be able to fall to the dewpoints
and begin to condense moisture. This is all a very favorable
setup for fog development, particularly where rain has occurred
in the past day or two. Recent model runs (RAP/HRRR) are
hinting at two areas where fog might be most favored. One is in
the southeastern CWA (including part of the area where the
advisory is already in effect) and another is in the
Miami/Whitewater valley regions (where there were some showers
today). To note, HRRR visibility projections have not been
wholly consistent on the location of dense fog development, and
SREF probabilities are focused south of the area. Overall, this
is a high confidence forecast for fog, though perhaps a medium
confidence forecast on the specifics for dense fog potential.
Previous discussion >
Main area of rain has moved east following a mid level trough
axis and band of low level convergence. This leaves lingering
isolated downpours that are erupting in a humid and unstable
airmass featuring negligible wind flow and high PWAT.
Once the showers dissipate this evening, light winds and
decreasing sky cover over the persistently humid low levels
will allow fog to form tonight. After collaboration with
surrounding offices, have decided to issue Dense Fog Advisory
for our Ohio River counties, with later shifts possibly
expanding coverage. Low temps dropping to the mid and upper 60s
are expected.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
After fog dissipates Friday morning, skies will become partly
to mostly sunny. Though weak high pressure should provide dry
weather for most locations, isolated showers may pop up Friday
afternoon in a humid regime containing marginal instability.
Look for warm highs in the mid and upper 80s, with lows Friday
night in the mid and upper 60s.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Mid level low over the upper Ohio Valley at the beginning of the
period will move further east over the weekend. This will allow
heights to rise, although there will be a short wave riding over the
top of the building ridge which will pass across the Great Lakes.
This short wave will be sufficient to push a weak boundary across
the region on Sunday. Some showers and thunderstorms may occur as
this boundary moves through with a better chance in eastern
counties.
Ridging will then expand up the Ohio Valley, but the southern edge
of the westerlies will be located across the lower Great Lakes. Weak
disturbances moving through this flow may result in convection both
Tuesday and Wednesday with higher chances in northern counties.
Weakness will develop in the mid level ridge by Thursday which may
be favorable for additional showers and thunderstorms areawide.
Above normal temperatures will persist through the period.
&&
.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
A few showers in the Cincinnati area are dissipating, and a few
showers in the Columbus area should dissipate by 02Z. Otherwise,
dry conditions are expected for the TAF period -- with just a
very low-end chance of a shower tomorrow afternoon.
The main concern for the TAFs is fog potential tonight into
Friday morning. Widespread MVFR to IFR fog is expected, with the
greatest chance of LIFR conditions at the Cincinnati airports.
Visibilities should improve to VFR by 14Z.
Winds will be light through the TAF period, generally 5 knots or
less.
OUTLOOK...Thunderstorms are possible on Sunday afternoon, and
again on Tuesday afternoon.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...Dense Fog Advisory until 9 AM EDT Friday for OHZ077>079-081-
088.
KY...Dense Fog Advisory until 9 AM EDT Friday for KYZ089>100.
IN...Dense Fog Advisory until 9 AM EDT Friday for INZ073>075-080.
&&
$$
SYNOPSIS...Coniglio
NEAR TERM...Coniglio/Hatzos
SHORT TERM...Coniglio
LONG TERM...
AVIATION...Hatzos
Area Forecast Discussion
National Weather Service North Platte NE
625 PM CDT Thu Aug 19 2021
.SHORT TERM...(This evening through Friday night)
Issued at 324 PM CDT Thu Aug 19 2021
The forecast concern in the short term will be the threat for strong
to severe thunderstorms mainly this evening along with the potential
for localized flooding this evening and overnight.
A large upper trough currently extends across the Great Basin in the
western U.S. with a closed low centered over northern Utah. Upper
ridging extends across the central and eastern U.S.
This upper trough will begin to move into the region tonight and
will bring a southwesterly flow aloft. A disturbance is forecast to
be across the western Panhandle and northeast CO late this afternoon
and lift northeast during the evening and overnight hours. A
southeasterly low level jet develops early evening and persists
overnight. Surface low pressure centered from east central and
southeast CO, will move into northwest KS late tonight. Deep layer
wind shear near 35KT is expected at the time of storm onset late
this afternoon. Regarding instability, MUCAPEs will range from 2500-
3500j/kg from late afternoon and evening through the overnight
hours. Initial storm development look to multicell and discrete
until mid evening will be surface based. Any discrete storms will
have the potential become rotating storms with the possibility of
a brief tornado or two. This looks mainly to be near and west of
Highway 61. Otherwise storms are expected to congeal into one or
two MCSs to move across the area overnight. This would pose a risk
for mostly damaging winds and isolated large hail possible. All
of western and north central NE is in a slight risk for severe
thunderstorms for tonight.
Given the indications of 1000-500mb thickness diffluence across
western NE, and the presence of a persistent low level jet,
sustained clusters of storms are expected and may train over the
same areas for 2-3 hours. With PWAT, on the conservative end from
1.25-1.5 inches, locally heavy rainfall is likely. Current forecast
has widespread QPF amounts from 0.75 to 1.25 inches north of a line
from Hayes Center through Broken Bow. The main forecast change from
previously is for higher POPs and QPFs forecast across southwest NE.
The latest several HRRR runs and the 18Z NamNest indicate the
heaviest rainfall amounts will be north of the surface low track
to extend across much of southwest NE. This area will need to be
monitored closely this evening and overnight for possible
flooding as rainfall amounts could exceed 3 inches locally. Areas
further north will also need to be monitored, however sandy soil
should lessen flooding concerns over most of the Sandhills.
On Friday, the upper trough axis will track through. Showers and
thunderstorms will lingering in the morning, with a chance across
the northeastern areas in the afternoon. Models have become more
progressive with the main upper trough lifting it northeast across
the Dakotas. SPC is forecasting a marginal risk for severe storms
east of Highway 183, and this looks to be a concern mainly during
the morning, as the cold front should be exiting far eastern zones
by 18Z. Highs on Friday will be much cooler behind the front from
the lower 70s northwest Sandhills to the lower 80s far southeast
zones.
Clear and cool Friday night as weak high pressure settles over the
region. Lows from 45 to 55.
.LONG TERM...(Saturday through Thursday)
Issued at 324 PM CDT Thu Aug 19 2021
The main forecast focus in the long term will be return of warmer
temperatures Sunday through Tuesday.
A dry forecast Saturday. The models are in fairly good agreement
bringing an upper trough into the Northern Plains Saturday night and
moving into the western Great Lakes by Sunday evening. This will
bring a 20-30 percent chances for showers/storms across portions of
western NE during this timeframe.
Looks dry again Monday into Tuesday with weak upper ridging and
seasonal temperatures in the upper 80s to mid 90s. An upper trough
is timed to cross the northern Plains again Wednesday and Thursday
with low POPs and a cooldown to the upper 70s to mid 80s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 619 PM CDT Thu Aug 19 2021
As with the previous update, the TAF period remains active. For
the terminals not yet seeing storms, winds are generally from the
east southeast ahead of the line. Gusts up to 25 or even 30 kts
are likely, and in fact some spots have already seen higher. Gusty,
erratic winds are possible with any t-storm, which is reflected
in KLBF`s TAF. Still expecting southern terminals to experience ~4
hrs of spotty LLWS around 2-6Z. T-storms have started in the
Panhandle and are moving to the ENE. Expecting to reach both
terminals around 2-3Z or so. Severe storms are possible bringing
hazards of heavy rainfall (that could reduce VIS at times), large
hail, and damaging winds. Storms and showers are expected to
linger through the morning, with reinvigoration in the afternoon
possible, but confidence is not as high. Lastly, given the wetting
from the storms, some low level fog and stratus are expected to
develop in the early morning hours and reduce VIS across the
Sandhills. Expecting LIFR and IFR conditions "at worst" for
southern (KLBF) and northern (KVTN) terminals, respectively. CIGS
and VIS should improve by late morning.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Roberg
LONG TERM...Roberg
AVIATION...Sinclair
Area Forecast Discussion
National Weather Service Lake Charles LA
1001 PM CDT Thu Aug 19 2021
.UPDATE...
Evening update.
&&
.DISCUSSION...
PoPs were adjusted slightly to account for current radar activity
as well as what the HRRR is showing. Isolated showers and
thunderstorms will be possible overnight for southern areas. High
pressure will continue to build into the area however which will
keep precipitation chances low through the day tomorrow.
55
&&
.PREV DISCUSSION... /issued 644 PM CDT Thu Aug 19 2021/
DISCUSSION...
00Z TAFS
AVIATION...
VFR conditions will prevail through the period. Lingering light
showers at AEX are expected to dissipate over the next hour.
Isolated convection will continue near the coast over the next
couple of hours. Any impacts to the coastal terminals are expected
to be very short in duration with most activity expected to
dissipate shortly after sunset. Light southerly winds will prevail
overnight. Wet soils and light winds could result in some light,
patchy fog shortly before sunrise. AEX, which has seen the most
significant rainfall today, will be most likely to see visibility
restrictions although these should be relatively minor. Any fog
will quickly dissipate within an hour of sunrise. Upper level
ridging will continue to build across the northern gulf Friday
which should serve to limit afternoon convection. While widely
scattered thunderstorms will be possible, the probability of these
impacting area terminals appears limited enough to omit from the
tafs for now.
PREV DISCUSSION... /issued 415 PM CDT Thu Aug 19 2021/
SYNOPSIS...
The latest UA analysis and WV imagery shows a ridge of high pres
extending west from the southeast US coast acrs the northern Gulf
coast. Drier air associated with the ridge is poised over FL and
into the northern Gulf of Mexico. Meanwhile, a lingering
disturbance remains on the northern periphery of the ridge, acrs
the ArkLaTex. Recent precip water analysis (LAPS Layer analysis
and GOES TPW) show an axis of very high PWATs (2.1 to 2.5 inches)
from NW LA southward into SE TX/SW LA, and this corresponds to
where the greatest coverage of convection is this aftn. The latest
KLCH and regional radar mosaic show sctd convection acrs much of
the area north of I-10, with more widespread activity acrs NE TX
and NW LA.
At the sfc, high pres is centered east of the area and this is
keeping light to moderate southerly winds in place, along with an
influx of low level moisture and elevated dewpoints. Temperatures
this aftn have reached the lower 90s, outside of any convection,
and combined with dewpoints in the middle and upper 70s, resulted
in peak heat index values between 102 and 108 degrees.
24
SHORT TERM [Tonight through Saturday night]...
Conditions will be trending hotter and drier over the next few
days as the ridge over the Gulf coast builds into the area. This
will help weaken the disturbance over the ArkLaTex and move it
away from the area.
Any lingering showers and storms late this aftn should dissipate
by around sunset. Drier air accompanying the ridge aloft should
limit nocturnal shower and tstm development over the nearshore
waters, but cannot rule out some isolated convection late tonight
near the coast.
Lower PWATs will continue to spread into the area on Friday,
falling to around 1.7-1.8 inches and closer to average for this
time of year. Despite this, enough moisture and instability should
be available for at least some widely sctd showers and storms to
develop during the day as the seabreeze moves inland. By Saturday,
the ridge is expected to become more centered over the area, and
the air aloft could be even drier, further limiting convective
development.
As convection and clouds decrease the next few days, daytime
temperatures Friday and Saturday are expected to climb into the
middle 90s during the aftn. Despite the increase in air
temperatures, diurnal mixing is expected to bring drier air and
lower dewpoints to the sfc, helping to keep apparent temps/heat
indices from bcmg too oppressive. While an isolated location or
two could see max heat index values at or just abv 108 degrees,
expect much of the area will stay below heat advisory criteria the
next couple of aftns.
While the tropics have become more active over the past week or
so, none of the systems pose a threat to the northwest Gulf of
Mexico. However, Grace, currently a Tropical Storm crossing the
Yucatan Peninsula, is expected to emerge over the Bay of Campeche
later this evening, strengthening back to a Hurricane by Friday
morning. Although Grace will pass well south of the area, the
extended fetch of southerly winds will result in elevated tide
levels near the coast from late tonight through late Friday night.
The latest probabilistic extra tropical storm surge guidance has
come in a slightly lower than previous fcsts, but tides are still
expected to be about 1 foot abv astronomical predictions. Tide
levels of 1 to 1 1/2 feet MHHW will be possible, mainly near
times of high tide. Given the marginal potential for tides to
reach or exceed 1 1/2 feet criteria for minor coastal flooding, do
not plan to issue a Coastal Flood Advisory at this time.
24
LONG TERM [Sunday through Thursday]...
Upper level ridge will begin to lose its hold over the gulf coast
region as we go day by day through extended period. Sunday will
be the last day of lower PoPs in the 10-30% range. By Monday as
the ridge shifts off, PoPs in the southeastern Parishes of our CWA
will ramp up to 30-50%. The rest of the work week will see an
increase in PoPs spreading across the CWA. Most of this will be
diurnally driven activity starting late morning / early afternoon
and tapering off in the evening.
Despite the ridge aloft shifting off a bit, we are still looking at
warmer temperatures. Afternoon max temperatures will reach into the
triple digits for a few areas north of the I-10 corridor on Sunday
and Monday. Heat indices will be in the 100 - 115 degree range. Some
areas will meet the criteria necessary for the issuance of a Heat
Advisory so please be safe while working outdoors.
Stigger/87
MARINE...
A light to moderate onshore flow will prevail through the
weekend as high pressure ridges across the northern Gulf of
Mexico. Shower and thunderstorm chances will decrease as high
pressure aloft builds over the region.
Tropical Storm Grace, currently over the Yucatan Peninsula, will
emerge over the Bay of Campeche and strengthen into a Hurricane
late tonight into Friday as it moves west. While the main impacts
of Grace are expected to remain well south of the area, the
increasing southerly fetch will bring increasing swells, which
will produce elevated wave heights especially over the coastal
waters beyond 20 NM. Exercise caution or advisory headlines may
be needed from Friday into early Saturday. Conditions should
begin to improve by Sunday.
24
&&
.PRELIMINARY POINT TEMPS/POPS...
AEX 75 95 74 98 / 30 20 0 10
LCH 78 93 76 93 / 20 20 0 20
LFT 77 95 76 95 / 20 20 0 20
BPT 77 93 76 93 / 20 20 0 20
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...None.
TX...None.
GM...None.
&&
$$
Area Forecast Discussion
National Weather Service Medford OR
823 PM PDT Thu Aug 19 2021
.DISCUSSION...20/00Z NAM in.
There are areas of marine stratus over the coastal waters and
along the north coast this evening and there is dissipating
stratocumulus from the Cascades east. Smoke continues to stream
from area wildfires. Flow aloft is turning northwesterly between a
departing inland trough and an offshore high.
An upper level trough will dig into the Pacific Northwest Friday
into Saturday, and this will support a front/marine push tonight
into Friday. This will bring drizzle or light rain to the
northwest facing slopes on the west side, mostly from the Umpqua
divide northward. The Siskiyous may get a bit as well. The marine
push will make Friday a bit cooler over the inland areas. The
NAM12 and GFS20 continue to suggest that extreme SE Lake County
may get clipped by some showers late Friday afternoon and evening,
so there is a slight chance of showers in the forecast for that
area.
As the trough digs over the area, a closed low will develop and
move into the Pacific Northwest Saturday. The models have been
trending faster with this trough, and now it is trending the
trajectory farther north as well. Therefore, it now looks like the
Medford forecast area will remain dry Saturday. It will also be
another relatively cool day inland with highs ranging from 5
degrees below normal to near normal values.
In the wake of the trough, weak residual troughing will persist
over the Pacific Northwest into next week. A warming trend will
begin Sunday with highs near normal to about 3 degrees above
normal. A flat ridge will build into the area from the southeast
Tuesday into Wednesday, so the inland warming trend will continue
through at least Wednesday, by which time inland highs will be 5
to 10 degrees above normal.
Then there is the wild card in the forecast...smoke. Air quality
monitoring sensors from both the Oregon DEQ and PurpleAir are
indicating that the HRRR and BlueSky Smoke Models have been
underestimating smoke production on earlier runs, especially east
of the Cascades. The DEQ expanded the Air Quality Alert to all of
Jackson and Klamath counties earlier today. Air quality will vary
quite a bit. It will be very poor at times, but there may be
periods of improvement that last several hours or more.
&&
.AVIATION...20/00Z TAFs...Along the coast, IFR ceilings will
continue through tonight as the marine layer pushes inland. We
expect the marine layer to make it into the Umpqua Valley and RBG
later tonight. It may also push into portions of the Rogue Valley
and MFR as well, although confidence is a little lower here.
Farther inland, smoke will continue to create MVFR visibilities near
terminals with brief periods of IFR. By tonight, we expect
visibilities to rise as the inversion prevents new smoke from moving
in. Plus the brisk surface winds should help push some of the
existing smoke away. Models show more of the same Friday afternoon
as fresh smoke from the fires moves in under northerly flow.
-Smith
&&
.MARINE...Updated 800 PM PDT Thursday, 19 August 2021...Gale force
north winds will continue south of Gold Beach through the end of the
week, with winds and seas highest in the afternoon and early
evenings. The thermal trough will weaken Saturday as an upper level
low swings north of the waters. As a result, winds should weaken
and seas should lower a bit, but still probably remain hazardous to
small craft south of Cape Blanco.
-Petrucelli/Smith
&&
.FIRE WEATHER...Updated 800 PM PDT Thursday 19 August 2021...
Northeast low level flow will continue through the night again
over the Coast Range, with moderate to good humidity recoveries.
This pattern will remain through the weekend, but wind speeds will
gradually decrease in strength each night.
A shortwave will bring a marine push tonight into Friday which
could result in another night/morning of accumulating drizzle
mainly for the ridges on the west side and mainly from the Umpqua
divide northward; including the Skyline and Devil`s Knob
Complexes. Confidence is not high that it will extend far enough
east to accumulate around the Jack Fire, but it should provide
good recoveries.
Overall, the upper level trough looks as if it will sweep through
faster than previously anticipated. This has resulted in a slight
chance of showers being added to the forecast in SE Lake County
Friday late afternoon-evening and any mention of showers and TS
being removed for Saturday PM.
By Sunday, a return to a westerly flow pattern is expected for
areas along and east of the Cascades. West of the Cascades,
northerly winds associated with a weak thermal trough will
return. Winds will be gusty in the afternoon, but much more
settled at night with weaker NE flow along the Coast Range.
Dry conditions with highs 5-10 degrees above normal will return
to inland areas next week, but temperatures will be moderated a
bit by smoke cover. East of the Cascades, especially in Fire
Weather Zone 625, afternoon RHs may drop near or into single
digits by mid-week.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.
CA...None.
Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT
Friday for PZZ350-356-370-376.
Gale Warning until 11 PM PDT Friday for PZZ356-376.
Hazardous Seas Warning until 11 PM PDT Friday for PZZ356-376.
$$
15/15/11
Area Forecast Discussion
National Weather Service Marquette MI
754 PM EDT Thu Aug 19 2021
.SHORT TERM...(This evening through Friday)
Issued at 329 PM EDT THU AUG 19 2021
Some fair weather cu are developing over the west and parts of the
east this afternoon. 17z observations also show weak lake breezes
currently moving inland along the lakeshores. WV imagery shows very
dry air aloft, which should prevent any precip from happening today
(the lake breeze shouldn`t be strong enough to produce convection
despite the dry air). This dry air is associated with a high
pressure ridge passing through the U.P. from west to east today,
tonight, and Friday. Therefore, partly cloudy to clear skies are
expected the rest of today and Friday. Skies should be fairly clear
tonight too. Could see some more cloud cover in the west tomorrow as
the ridging begins to weaken and a trough from the west approaches.
One thing worth mentioning is that the HRRR smoke model is showing
quite a bit of vertically integrated smoke over us today, tonight,
and Friday. Therefore, increased the cloudiness over us in the sky
grids to handle the haze today through Friday.
Temperatures today and Friday should be similar to what we saw
yesterday. A lot of the U.P. could approach 90F, particularly the
southerly downslope areas near Lake Superior tomorrow (as winds
tomorrow are expected to be southerly pretty much the whole day
across Upper MI). Lows tonight should hang around the 60s across
most of the area, with the cold spots in the interior west possibly
dipping into the upper 50s. Given that the haze didn`t seem to have
much of an affect on temperatures, kept temperatures as-is from the
previous shift (Hi-res guidance and 90th percentile temps).
.LONG TERM...(Friday night through Thursday)
Issued at 331 PM EDT THU AUG 19 2021
Models indicate the amplified mid-upper level pattern currently over
the CONUS will break down late this week with a progressive, quasi-
zonal flow setting up over the northern CONUS and Upper Great Lakes
region late this weekend into the middle part of next week. The
pattern transition will result in a series of shortwaves moving
across the Upper Great Lakes this weekend into next week.
Unfortunately, weak dynamics and/or limited moisture with these
shortwaves will probably not produce much rainfall and prolong our
ongoing dry stretch another week or so. Temperatures will trend from
above normal Saturday to normal or slightly above normal Sunday
into the middle of next week.
Beginning Friday night and Saturday, central/northern Plains
shortwave approaches late Fri night and then moves across the cwa
along with its associated cold front on Saturday. Even though PWATs
approach 1.5 to 2 inches ahead of the front, models indicate the
best dynamics staying well north into Canada so model qpf fields
still only depict a broken line of light showers moving across the
cwa Saturday into Saturday evening. Suspect many locations will
struggle to see any measurable rainfall. With CAPE values fcst 500-
1000 j/kg it is possible there could be a few thunderstorms,
although expect better instability and shear for any stronger storms
to stay southwest or west of the area closer to the track of the
vort max with the shortwave. Tight gradient and gusty southerly
winds ahead of the front could maybe result in a moderate swim risk
for Lake Mi beaches in Schoolcraft Co on Saturday. After Friday
night`s min temps in the 60s, expect Saturday max temps generally
ranging from the mid 70s to the mid 80s under increasing cloud
cover, coolest far west and near Lake Mi.
Saturday night into Sunday, models indicate any remaining showers
ending early evening in the east, then dry, cooler and less humid
conditions thereafter into Sunday as sfc high pressure builds in
quickly from the west behind Saturday`s shortwave/cold front. Min
temps Sat night will fall back into the more comfortable 50s for
most locations. Sunday`s max temps will be closer to seasonal
normals with highs in the 70s.
Models show reasonable agreement with another shortwave and warm
front moving in late Sunday night into Monday, but similar to
Saturday`s system the best dynamics will stay west and north and it
looks like we will get little, if any rainfall. Much more model
uncertainty with timing/strength of next shortwave due in on
Wednesday and degree of cold air behind the system for late next
week, so for now, will stick with model blend for forecast details.
Gut feeling is moisture will probably be fairly limited again with
midweek system, so not expecting any meaningful rainfall.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 741 PM EDT THU AUG 19 2021
Outside of the potential for some more shallow fog tonight at
KSAW, VFR conditions are expected to prevail at all three
terminals through the TAF period. Southerly winds will be on the
increase tomorrow ahead of an approaching disturbance. Expect
another afternoon of diurnally-driven CU tomorrow.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 235 PM EDT THU AUG 19 2021
Surface high pressure should keep winds under 20 knots until Friday
evening. Then, as a trough approaches the lake on Friday night,
expect southerly wind gusts to increase to around 20-25 knots. As a
cold front associated with the trough moves through Saturday
afternoon and evening, expect the winds to become westerly right
behind the front Saturday afternoon, before becoming northwesterly
Saturday night. Could see some gusts up to 30 knots on the elevated
observation deck carriers on Saturday afternoon and evening. Behind
the cold front Sunday morning, expect winds to become 20 knots or
less. Wind speeds should remain 20 knots or less for the remainder
of next week.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...TAP
LONG TERM...Voss
AVIATION...lg
MARINE...TAP
Area Forecast Discussion
National Weather Service Pocatello ID
237 PM MDT Thu Aug 19 2021
.SHORT TERM...Today through Saturday night. Looking at satellite
imagery there is an upper level low over northern UT/Southern
Idaho that is bringing moderate to heavy rain from south of Idaho
Falls to near Rockland. Already 0.50 to 1.00 of rain has fallen
along the Eastern Highlands and the Snake River plain this
morning through early this afternoon. Expect another 0.25 to 0.50
of rain this afternoon before tapering off, mainly in a line
starting west of Blackfoot going south through Pocatello/American
Falls and ending near Rockland. Please use caution in low lying
areas where ponding of water is likely, especially in areas that
have mostly pavement.
This upper level low moves northeast lifting into northwest
Wyoming by this evening. Expect gradually tapering off of
precipitation over the Snake Plain/Southeast Highlands by this
afternoon into early this evening with the precipitation
lifting/moving to more of the Island Park area through this
evening into Friday morning. Expect drier northwest flow tomorrow
over our area with lingering, overall light, precipitation mainly
over the Montana Divide.
By Saturday another system or trough moves into the area starting
to bring precipitation early Saturday morning and then spreading
through the the entire forecast area by Sunday morning. In
general, expect 0.10 to 0.30 inches of rain over most of the area,
though the Eastern Highlands could get 0.50 inch of rain or
slightly more. Breezy to moderate winds and isolated to scattered
thunderstorms are expected as well.
Temperatures are 20 to 30 degrees below normal today and will rise
tomorrow and Saturday but will still be a good 10 to 15 degrees
below normal.
Wyatt
.LONG TERM...Sunday through Thursday. The forecast continue to
remain on track for early next week. The low will be moving east on
Sunday, with lingering showers and storms along the Wyoming and
Montana borders in the afternoon. Things for Monday have changed too
much either with the low across southern Canada and a weak trough
lagging back across the Pacific Northwest and northern Rockies. This
keeps a low chance of showers and storms along the Montana border
and across the eastern and southeast highlands. This should slow
down the warm up a small amount early on. The forecast for next week
has taken an interesting turn. All of the models and cluster
forecasts were going with a building ridge. Now, there is some doubt
creeping in about that. The majority of the cluster forecast still
has a ridge of some sort over us midweek. However, some of the
cluster forecasting is showing some sort of trough now moving
into/through our area. Both the "operational" GFS and ECMWF are now
showing that. The Blend of Models is showing the drier forecast. We
will stay the course for now, but if we end up with another trough
moving through...it may not necessarily be wet but it could be
cooler than the current forecast.
Keyes
&&
.AVIATION...With the low across southeast Idaho, some areas have
seen widespread rain and MVFR/IFR conditions...and occasionally LIFR
due to visibility and ceilings. This includes PIH, IDA and DIJ. It
appears now that rain/thunderstorms may NOT reach BYI and SUN. We
do have at least VCSH in the forecast. It won`t be until later
tonight, potentially closer to 12z Friday, for this to clear out.
The question will then be could there be fog/stratus in its wake. At
the moment, we aren`t expect anything widespread but some lower
clouds are likely. Another round of showers and storms is possible
tomorrow, mainly impacting DIJ.
Keyes
&&
.FIRE WEATHER...The main impacts from this storm have remained
farther east that anticipated today and with this storm so far. At
this point, we may not see the wetting rains across our central
mountain and south-central fire zones, even with anything that
develops today. We will be in between lows Friday, with lingering
showers and isolated thunderstorms across most of the central
mountains, Zone 411, and maybe as far south as Bear Lake in 413. The
next low impacts Saturday through Sunday. This storm has the
potential of producing wetting rains once again across portions of
the central mountains and eastern/southeast highlands. This storm is
moving faster than the current one, so we may need to take that into
account in terms of how much rain we might get. At this point, once
again wetting rains are LESS LIKELY for south-central Idaho and
portions of the Snake Plain. We will be monitoring fuels and
forecast trends, and see if we MIGHT need a Red Flag Warning for
some areas due to potential for scattered storms on Saturday.
Lingering showers and storms are expected Sunday and again Monday
along the Montana and Wyoming borders. Temperatures will begin
warming up, even with the next low coming in this weekend, but we
likely won`t be back to around or above average until the middle of
next week.
Keyes
&&
.AIR STAGNATION...Overall we have seen improving air quality over
the area due to precipitation and a change in wind direction
aloft. However, most of our area is currently in the moderate
category with air quality slightly worse over the Eastern
Highlands. But again, this should improve today because of
precipitation and a continued gradual change of wind direction
aloft. HRRR smoke model shows some more smoke moving into the
area in northwest flow early this evening but improving Friday
morning and then potentially getting much worse with smoke coming
into the area from California in Southwest flow Saturday morning
ahead of the next system.
Wyatt
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Pueblo CO
552 PM MDT Thu Aug 19 2021
.UPDATE...
Issued at 542 PM MDT Thu Aug 19 2021
The Severe Thunderstorm Watch for El Paso, Kiowa, and Prowers
Counties has been cancelled. Chances for thunderstorm development
will continue to decrease early this evening, as stronger forcing
for ascent continues shifting northeast of the area, and
convective inhibition nocturnally increases. No other changes
have been made to the ongoing forecast.
&&
.MESOSCALE DISCUSSION...
Issued at 247 PM MDT Thu Aug 19 2021
Main Points:
-An upper level low, with a wave out ahead, will have big impacts on
today`s weather.
-A dryline is set up over parts of the eastern plains, which
increases our chances for severe weather this afternoon.
-The upper low, the wave, and the dryline have challenging
interactions that make today`s forecast complicated, and the usual
models may not handle it well, resulting in a lower confidence, yet
potentially higher impact forecast.
A challenging forecast setup over our area today, with a lot of low-
end possibilities of varying outcomes. Our main forecast challenges
will mainly stem from the upper-level low pressure center to our
west, slowly lifting to the northeast, as well as the dryline that
will set up near the Colorado-Kansas border today. Where the
complications to the forecast come in will be described through the
relationship between the upper-level features, resulting moisture
advection, low and mid-level winds, and the impacts all of this has
on the dryline and related convective activity.
First, looking at the synoptic-scale features. The upper-level low
and associated trough are slowly moving northeast, while
simultaneously become slightly more negatively tilted. Additionally,
out ahead of the main low there is a separate, somewhat fragmented
wave. The wave is moving over our area in pieces, which will inhibit
surface cyclogenesis and downslope flow over the eastern mountains.
With regards to the dryline, this should weaken the moisture
gradient somewhat, resulting in a less `sharp` dryline. However,
with the upper trough being more negatively tilted, it has the
impact of making 700mb winds more southerly over the plains, while
also advecting in more synoptic moisture. This has several effects.
First, while winds today over the plains are expected to veer with
height, giving the low to mid level winds more of a southerly
component will allow for parcels traveling over the dryline to have
a longer residence time; rather than hitting the dryline circulation
and having stronger westerlies aloft push them out, the parcels will
have more of a south-north oriented path, allowing for a higher
chance of air parcels remaining along that dryline circulation long
enough to better support convective initiation.
The weaker westerly downslope off of the mountains and suppressed
mixing due to the progression of the upper-level wave will have a
significant impact on the western extent of the dryline. Most of the
processes involved with the dryline and the boundary layer are, for
the vast majority of models, sub-grid scale processes. As such,
convective-allowing models, such as the HRRR, that resolve boundary
layer mixing explicitly within their model physics, are actually
unable to capture these processes properly. As a result, many of the
CAMs have a tendency to overmix the boundary layer, causing the
dryline to eject eastward far too early. In this case, CAMs will
have lower value in the forecast process, and models that
parameterize PBL mixing, such as the GFS, will actually have more
value in this situation.
Looking at the dryline itself, a few additional details play into
its behavior through the rest of today. First, observed pressure
falls span more to the south than models have been indicating, with
noticeable values down to near Trinidad. While the dryline is not
anticipated to extend that far south, it is not out of the realm of
possibility for it to extend down to around Highway 50.
Additionally, with westerly downsloping wind expected (even though
they will not be as strong as once expected), there exists the low-
end chance for an interesting phenomenon. With recycled moisture
around the lee cyclone as well as the upper-level low circulating
into those westerly downslope winds, there exists the chance for a
secondary moisture gradient to set up slightly west of the main,
proper dryline. This would effectively, result in a `double dryline`
setup. What this means is that, were this to happen, convective
initiation would be able to occur further west than any of the
models or mesoscale analysis would suggest. The NAM specifically
this morning did hint at the possibility, and mesoscale components
do support it, although due to the myriad of necessary factors the
confidence for such a situation occuring is low.
As that upper-level fragmented wave pushes through the area just
ahead of the low, a secondary weather concern exists this afternoon
over El Paso County and the Palmer Divide. A steady cu field is
already building in over the area, so the chances of significant
impactful weather there is very low with very limited instability
and solar heating. However, guidance has been consistently resolving
an area of low-level convergence on and just north of the Palmer
Divide. Given these conditions, even if the chance is low, if a
storm does manage to fire up there, locally heavy rain as well as
some small hail would be possible.
Looking at the target areas for today, the dryline currently appears
to be sitting around the Eads area, extending south through Prowers
County. This will be the main area of concern for today, and we will
have to pay very close to the progression of the dryline as daytime
mixing occurs, taking into account the influences listed above. The
Palmer Divide does have a chance of supporting some storms this
afternoon, but the chances are much lower as of now. Two potential
scenarios for the next 6 hours or so can be presented as follows:
The worst case scenario (LOW confidence): A secondary dryline sets
up behind the initial circulation, and severe storms fire in Kiowa,
Bent, and Prowers Counties, resulting in 2 inch hail, 70 mph winds
and a weak isolated tornado. Low-level convergence also manages to
spark storms over northern El Paso County, which sees heavy rain,
hail up to 1 inch, and winds up to 60 mph.
More likely scenario (MEDIUM-LOW confidence): The dryline remains
near where it is now, moving slightly east over the next few hours.
A few stronger, isolated storms form somewhere between Holly and
Eads, with hail up to golf ball sized and winds around 60 mph.
Storms quickly move north and east out of the area in accordance
with the general steering flow. Few, if any, storms fire over the
Palmer Divide in our forecast area.
&&
.SHORT TERM...(This evening through Friday)
Issued at 247 PM MDT Thu Aug 19 2021
Currently, some convective initiation has already begun over parts
of El Paso County and the Palmer Divide, as well as the dryline.
Will continue to closely monitor conditions over the next few hours.
Looking at soundings on the east side of the dryline, the HRRR is
resolving close to 200 relative helicity, meaning that the concern
for tornadic activity has increased slightly. Additionally, the axis
of the moisture boundary over El Paso has not moved as far north as
some of the guidance had indicated, and therefore the chances of
more impactful weather in that area have also increased. Several
storms have already fired in the area, although nothing worthy of a
report has occurred thus far.
As a result of these developing conditions, the Severe Thunderstorm
Watch now includes Kiowa, Prowers, and El Paso Counties.
-See the Mesoscale Discussion section of this AFD for a more in-
depth analysis of ongoing conditions with regards for convective
weather through this evening.
After convective activity ceases for the day, precipitation over the
eastern half of our area will wane and the dryline will eject to the
east. Tonight, precipitation will persist over the Continental
Divide and the San Juan Mountains, which could potentially pose some
concerns for burn scar flash flooding if showers manage to train
over those areas. Otherwise, the precipitation will last into early
morning before waning. Snow levels were down around 11kft in some of
the guidance over some parts of the San Juans, so there does stand a
chance for some snow accumulation over the highest peaks tonight.
.LONG TERM...(Friday night through Thursday)
Issued at 247 PM MDT Thu Aug 19 2021
Main upper trough is expected to pass through early on Friday, with
the area on the back side of this system by midday and early
afternoon. This setup along with the loss of higher moisture should
limit much of any precip development on Friday, and so have
continued the trend of decreasing pops early Friday. Any snow
occurring across the central mountains is expected to end by the
start of the period, with any snow accums once again expected to be
light. Slightly cooler air mass expected to be in place on Friday,
with temps falling back towards more normal conditions. Conditions
still expected to remain mainly dry Friday night into Saturday,
though some guidance is trying to develop some light qpf across the
Palmer Divide during this time. Would anticipate this to likely be
more increases in low level cloud cover, though can`t completely
rule some light shower develop given increases in moist upslope
flow.
Cooler temps and mainly dry weather expected going into the weekend.
Dry weather expected for most areas into early next week, though
temps rebound with above normal temps once again expected across
southern CO. Active weather is appearing to return to southern CO by
next week, with above normal temps persisting.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 247 PM MDT Thu Aug 19 2021
VFR and mainly dry conditions still expected across the TAF sites
this period. Once again, think mainly dry conditions though some
scattered showers and maybe an isolated thunderstorm still can`t be
ruled out through early evening for ALS and COS. Confidence is still
low at this time though. Will continue to keep a close eye on
trends, and adjust the forecast as needed. Gusty southerly winds
expected to continue through this evening, gusting to as high as
around 30 kt.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...COHEN
MESOSCALE...GARBEROGLIO
SHORT TERM...GARBEROGLIO
LONG TERM...RODRIGUEZ
AVIATION...RODRIGUEZ
Area Forecast Discussion
National Weather Service Reno NV
1200 PM PDT Thu Aug 19 2021
.SYNOPSIS...
Expect mild summer temperatures with some afternoon and evening
breezes over the next week. Gusty southwest winds are expected
late day Friday into Saturday due to another cold front with
increased fire weather hazards. Unfortunately these winds will
push wildfire smoke back into the region tomorrow afternoon and
evening.
&&
.DISCUSSION...
Smoke returns...
Best advice is enjoy the relatively good air quality and the cool
summer weather today and tomorrow morning. More widespread
wildfire smoke is forecast to return tomorrow afternoon into
Saturday morning as low pressure moving into the Pacific
Northwest switches the flow to the west-southwest. Expect periods
of moderate to poor air quality depending on fire activity.
Simulations remain undecided on how much ridging builds across the
west next week. Some simulations keep a trough along the west
coast for the next 7-8 days. Even if a ridge develops over the
Desert Southwest the flow aloft will remain out of the southwest
and maintain smoke transport into eastern Sierra and western NV.
Temperatures...
There is no significant warm up in the forecast until later next
week. Afternoon highs will hang around the low-mid 90s across
western NV with 80s in the Sierra. Overnight lows will dip into
the 30s for the Sierra valleys with 40s-50s elsewhere.
Winds...
Low pressure to our north will increase winds with a cold front
brushing northern Nevada. Breezes will increase tomorrow
afternoon with gusty winds possible most of Saturday. Expect some
gusts up into the 30-35 mph range, so be mindful if you plan to go
out boating. Light afternoon/evening breezes will hang around for
most of next week.
Staying dry...
Only chance of precipitation is just a few showers (5% chance of
a thunderstorm) up in the Surprise Valley and far northern Washoe
County as the front passes Friday night and Saturday. Brong
&&
.AVIATION...
* VFR persists through the evening and much of the day Friday with
east/northeast flow keeping much of the smoke out of the region.
There will likely be some periods of haze due to the extensive
fires and smoke in the west, but not anticipating significant
visibility restrictions through midday Friday.
* On Friday afternoon, west to southwest winds will bring an end to
the smoke break, as another trough approaches the West. Based on
the current fire activity and HRRR Smoke model, we could see
periods of MVFR to possibly IFR smoke after 22z/Fri to areas
around TVL, CXP, MEV, and SVE, and possibly TRK/RNO areas after
0z/Fri. Haze possible elsewhere but predictability is limited this
far out, and also highly dependent on latest fire activity.
* Unfortunately, smoke and haze that filter in late Friday will be
around with ongoing visibility impacts into Saturday.
-Edan
&&
.FIRE WEATHER...
* Main concern is with increasing winds Friday night into Saturday
as another cold front approaches the region. The cold front is not
as strong as the one earlier this week, but the winds still raise
concerns for localized critical conditions.
* Friday will be a more typical zephyr-wind type day with very
localized critical areas along the Sierra Front wind prone spots
for only an hour or so. The primary day of concern is Saturday
where there is potential for 2-4 hours of critical winds and low
humidity for areas across W Nevada and portions of NE California.
ECMWF EPS guidance continues to show quite a few members with
gusts 35 MPH in W Nevada on Saturday.
* We are going to continue to headline the wind/RH risk for Saturday
in the FWF, but the event overall still appears to be marginal in
regards to limited duration, marginal RH values, and intensity of
the winds.
* Of note: The extensive smoke plumes have also been `toying` with
the surface temperatures as of late. As the smoke pushes into the
Sierra and Sierra Front again on Friday afternoon, it will likely
moderate temperatures a bit and influence the strength of the
surface winds by Saturday as well.
-Edan
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno
Area Forecast Discussion
National Weather Service Topeka KS
609 PM CDT Thu Aug 19 2021
...AVIATION UPDATE...
.DISCUSSION...
Issued at 342 PM CDT Thu Aug 19 2021
...Strong to Severe Storm and Excessive Heat Expected Friday...
As of 20Z Thursday afternoon, an upper-level shortwave ridge axis
extended from the northern Great Lakes through southern KS/MO.
Meanwhile a weak mid-level perturbation was progressing northeast
through north-central OK and southern KS. This feature was aiding in
widely scattered shower and thunderstorm development across much of
the forecast area. Fortunately, effective shear remains minimal and
severe storms are not expected. Meanwhile, a stronger mid-level low
resided across northern UT. Thunderstorms were developing along a
deepening surface trough across the High Plains of CO and WY was
contributing to thunderstorm development. Short term model solutions
suggest these storms will grow upscale and progress eastward along
the forward propagating MCS vectors -- keeping the bulk of
convection north of the NE border.
Transitioning into tonight, a strengthening LLJ will overspread the
area from west-to-east after 06Z. Isolated thunderstorms may develop
along the LLJ convergence axis. Effective shear appears to be weak,
therefore, expected pulse convection. Overnight lows look to reach
the low to mid 70s.
A multi-hazard day and evening is in-store for much of the area
Friday. The first concern will be excessive heat and humidity. The
aforementioned surface trough axis will approach the forecast from
the west by midday. Surface dew points are progged to remain in the
low to mid 70s with temperatures surging into the low to mid 90s
ahead of the front. Coupling the two will result in heat index
values exceeding 100 degrees. As a result, a Heat Advisory goes into
effect from 18Z Friday through 00Z Saturday for areas generally
along and southwest of a line from Concordia to Topeka. The second
hazard will be the potential for severe thunderstorms during the
late-afternoon and evening. The aforementioned mid-level low across
northern UT will propagate through the central and northern Plains
as a shortwave trough Friday afternoon and evening. Sufficient
surface convergence along the surface trough along with modest
ascent from the shortwave trough should allow thunderstorms to
develop along the front from SD through southern KS between 21-00Z
tomorrow. MLCAPE is forecast to range from 3000-4000 J/kg with a
modestly veered wind profile yielding around 30 kts of effective
shear. Initial discrete or semi-discrete cells are likely to grow
upscale as cold-pools merge and propagate ESE. This will transition
an initial large hail and damaging wind threat to a damaging wind
and flash-flooding threat. The bulk of thunderstorm activity is
forecast to exit the area by dawn Saturday morning.
For Saturday and beyond, a surface ridge axis will overspread the
area Saturday into Sunday while a mid-level ridge axis expands over
the southern Plains. A strengthening LLJ late Saturday night could
result in a few storms across the area. Additional storms will be
possible late Sunday afternoon and evening as a secondary shortwave
trough propagates through the northern Plains. Otherwise, a drier
pattern is probable as the southern US mid-level ridge expands
across the forecast area. Temperatures will also be on the increase
as afternoon temperatures are forecast to reach the low to mid 90s
Monday-Wednesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday)
Issued at 609 PM CDT Thu Aug 19 2021
A low level warm air advection pattern is forecast to bring in
MVFR CIGS along with a small chance for elevated showers. The RAP
and NAM are in good agreement with low levels becoming saturated.
So will include a MVFR CIGS moving in prior to sunrise. Looks like
these CIGS could hang around into the early afternoon for TOP and
FOE. There is also a good signal for theta-e advection along with
isentropic lift late tonight and Fri morning. Although CAMs are
not that impressive with coverage. And the 12Z HREF keeps the
potential for showers generally around 30 percent and for areas
near and west of MHK. So will include a VCSH at MHK and leave any
precip mention out of the forecast for TOP and FOE. Convection is
likely to fire along a frontal boundary in northern KS. Model
consensus has this occurring late in the period with it impacting
the terminals near of just after 00Z Saturday.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM to 7 PM CDT Friday for KSZ020>023-
034>039-054-055.
&&
$$
DISCUSSION...Baerg
AVIATION...Wolters