Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/21/21
Area Forecast Discussion
National Weather Service Gaylord MI
915 PM EDT Fri Aug 20 2021
.UPDATE...
Issued at 915 PM EDT Fri Aug 20 2021
High pressure remains centered over the Great Lakes and the Ohio
Valley late this evening...maintaining our persistently clear and
quiet wx. Little will change overnight...but do expect areas of
fog will again develop into early Friday morning. Low temps
tonight will cool into the low to mid 60s.
&&
.NEAR TERM...(Through Tonight)
Issued at 335 PM EDT Fri Aug 20 2021
High pressure is over eastern lower MI and environs, drifting
east. The high reaches the eastern lakes overnight. Return flow
will develop tonight in the wake of the high, especially over/near
Lake MI and eastern upper MI. Presently, there is only a little cu
out there today (less so than yesterday), though there is plenty
of haze/smoke aloft.
Paltry cu will dissipate this evening, with limited cloud cover
otherwise. Overnight, some marine fog/stratus could reform again
(like this morning). This is most likely in the Straits area, and
adjoining parts of Lakes MI/Huron. Patchy fog will form elsewhere,
though not as much as the past couple of nights, given the
gradually tightening pressure gradient during the night.
Another muggy night ahead, with lows in the 60s, nearly 70f near
Lake MI.
&&
.SHORT TERM...(Saturday through Monday)
Issued at 230 PM EDT Fri Aug 20 2021
High Impact Weather Potential: Minimal, save for some small thunder
potential late Saturday...
Pattern Synopsis/Forecast:
Saturday morning...split flow aloft remains intact over the eastern
US...with ridge axis more or less along the Ontario/Quebec border
and troughing south of there, centered over the Mid-Atlantic
states...with Henri getting absorbed into the overall flow as it
makes a beeline for the New England coast. Shortwave troughing
lifting through the Upper Midwest Saturday will lead to our next
"best" potential for rain/storms Saturday night (naturally)...as
another shortwave dives into the Pacific northwest. Additional
shortwaves look to dip into the trough out west through the
remainder of the period...which may bring additional shower/storm
chances into the start of the next workweek. Though our shortwave
from Saturday night may weaken it...somewhat anomalously strong
ridging over eastern Canada this weekend may yet prove to block
troughing associated with Henri (and the lower half of our recent
split flow)...potentially leading to minimal changes in the
downstream pattern into the long term portion of the forecast.
Primary Forecast Concerns: Rain/storm potential Saturday
evening/night...
Seeing as how we ended up with virtually no precip over the last 48
hours, pretty much CWA-wide...am currently suspecting the trend of
drier-than-expected will continue. This seems relatively reasonable,
as the chance of even 0.01" of 24-hr QPF (rainfall totals) seems
limited to maybe a 40-60% chance for much of Northern Lower, based
on some probabilistic guidance. Slightly better potential exists
across the UP/Eastern UP where better moisture should be located
closer to better dynamics/forcing as the shortwave itself skirts us
to the north, over what remains of ridging that will have been
broken down/shunted southward...between the approaching shortwave
and troughing associated with Henri to our southeast. That being
said...there are some signals for a tiny bit of upper level
divergence ahead of the shortwave/resultant surface cold front
Saturday afternoon/evening...more or less co-located with the plume
of higher moisture as it moves in from the west...which suggests
that we can`t completely write off Saturday as dry...especially with
Pwat values approaching 1.8" again (which would be pretty much the
max end of climatological norms for this time of year)...though the
best moisture should (seemingly as usual) split around us...and many
areas will remain dry and/or see very minimal precip. Still...with
anomalously strong deep moisture passing through...wouldn`t be out
of the question for some areas to squeeze out a bit more QPF with
any of the more vigorous showers/storms.
The third ingredient for precipitation, instability, seems to be
lacking overall...as we may just barely get warm enough at the
surface here in Northern Michigan Saturday afternoon to be able to
finally overcome the cap (maybe) and generate some surface based
instability for a change...though it may not be much. Most guidance
seems to keep it under 1000 j/kg of surface-based CAPE...perhaps
well under 1000 j/kg...though we`ll see how much surface heating
we`re actually able to get in on. Worth noting that today, despite
the smoke plume aloft...temperatures are still reaching into the mid
to upper 80s inland...with some diurnal cu even beginning to develop
across the area as of 2pm. Do believe we should be able to reach our
full surface heating potential Saturday...especially as HRRR smoke
guidance suggests that as winds become more southwesterly ahead of
the front, less smoky air would be advected into the region...thus,
bluer skies would be the norm. However...there are also some signals
that the cap may ultimately remain in place in some parts of the
area, despite surface heating, as it should be warm enough aloft to
squash much development aside from general cumulus. It should be a
little breezier Saturday as the pressure gradient tightens a tad in
response to the approaching system...especially across northern
sections of the CWA. Not sure if it will be strong enough to keep
lake breezes from cropping up and lending additional sources of
forcing to the equation...so we may have to keep half an eye on that
as well.
As far as timing goes, looks like the best moisture (which seems to
be dwindling, per the latest model runs) should begin to cross Lake
Michigan perhaps as early as mid-afternoon...though mid-level
moisture seems to diminish as it crosses the lake, with low-levels
becoming more saturated with time. (As alluded to above...wouldn`t
be out of the question to see some diurnal pop-ups in the afternoon
as well, ahead of the main line, which should move through later.)
There is still some uncertainty in timing, however...with some
guidance a bit quicker than others. It should be a rather slow
progression across the CWA...perhaps with some of our sunrise side
areas still experiencing the rain/clouds by sunrise (or later)
Sunday, depending on how quickly the cold front departs in the
morning. Behind this...looks like we should see some subsidence and
a bit of cold advection...which should make for a much more pleasant
Sunday than Saturday.
Going into Monday, things become tricky again...as the niblet
currently diving into the Pacific northwest as of 20/12z will have
made it through the flow and be approaching the Great Lakes by
Monday. Similar to Saturday`s situation...looks like this system,
too, may be a bit on the moisture-starved side...with the best
forcing staying to our north...though there are still some timing
and strength differences. Will be watching for this niblet to try to
pick up the troughing/Henri to our east...and drag it on its way
going into the long term.
.LONG TERM...(Monday night through Friday)
Issued at 230 PM EDT Fri Aug 20 2021
High Impact Weather Potential: Minimal attm...
As mentioned at the end of the short term...will be watching
Monday`s niblet of energy to attempt to drag Henri out of New
England...with ridging holding on across the southern US...keeping
much of the activity across the northern tier of the
CONUS/international border. Some of these niblets of energy may be
able to supply us with rain/storm chances in the coming
days...though there is still enough uncertainty that some of the
details...such as timing and strength of the niblets...will stay at
low resolution for a while, until things become clearer in the
coming days.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 700 PM EDT Fri Aug 20 2021
High pressure will slowly slide east away from Michigan tonight...
followed by an approaching cold front that will reach Lake
Michigan by Saturday evening. Areas of fog will again develop late
tonight into early Saturday. Otherwise...expect mainly VFR
conditions. Chances of showers and storms will begin to increase
later Saturday afternoon across NW Lower Michigan...but the chance
is too low to include in the TAF forecast for now. Light/variable
winds tonight will become southerly at around 10 kts on Saturday.
&&
.MARINE...
Issued at 230 PM EDT Fri Aug 20 2021
High pressure will slowly move east, and a southerly breeze will
gradually increase on Saturday. Advisory-level winds/waves are a
possibility Sat afternoon on some of our Lake MI waters, as well
as on Whitefish Bay. An abrupt shift to a northerly breeze takes
places Sat night, as a weak cold front moves thru.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&
$$
UPDATE...MR
NEAR TERM...JZ
SHORT TERM...FEF
LONG TERM...FEF
AVIATION...MR
MARINE...JZ
Area Forecast Discussion
National Weather Service Binghamton NY
944 PM EDT Fri Aug 20 2021
.SYNOPSIS...
Warm and humid weather continues right through the weekend with
more pop up showers and thunderstorms around, especially in the
afternoon and evening hours. Watching tropical storm Henri
closely as it may bring additional periods of rain to parts of
the region later Sunday into early next week.
&&
.NEAR TERM /THROUGH SATURDAY NIGHT/...
950 PM Update...
Updated PoPs and blended the forecast with the HRRR since it
seems to be handling the rain showers moving into the Catskills
region well. Rainfall is expected to be light, largely under a
quarter inch in regions that do receive rain. A few showers and
thunderstorms have been stubborn to move out of Steuben county
with radar estimates of up to 2 inches over the last 3 hours so
a flood advisory was issued. The showers are on the move and
will clear the affected region over the next hour or so.
800 PM Update...
Small changes to PoPs this evening but kept most areas 15-30%
PoPs for coverage. Showers are isolated and slow movers so most
locations will stay dry. Also added in some more fog this
evening along the river valleys since there could be a few hours
of clearing tonight to help radiate below the crossover
temperatures for fog.
310 PM Update
It looks to remain rather cloudy along and east of I-81 into the
evening hours; with more partial clearing back to the west. We
have 2 cloud layers this evening; some thicker high level clouds
across the central and eastern portions of the area, then
scattered to broken cumulus clouds underneath the high clouds.
Latest radar and surface obs are also showing, as expected some
isolated, pop up showers across the area, and a stray thunderstorm
is also possible through about sunset. MLCAPE is only 250-500
J/Kg and LIs somewhat unstable, mainly -1 to -3 across our CWA.
Shower/t`storm movement is north to south around 20 mph. Most
locations should end up staying dry this evening.
Overnight should be generally quiet, with just an isolated
shower or storm possible. Otherwise, mostly cloudy with patchy
fog around and humid. Lows back down into the mid and upper 60s.
For Saturday, the slow moving upper level low/trough will be
over the region. This should combine with the warm, humid and
unstable air mass to produce scattered showers and thunderstorms
across the forecast area...mainly in the afternoon and evening.
PWATs rise back up to around 1.85 inches, and with somewhat slow
storm movement (SE to NW this time) there could be locally heavy
rainfall and frequent cloud to ground lightning. Deep layer
shear remains low, less than 20 kts, so severe storms are not
expected at this time. WPC does have much of our area under a
marginal risk for excessive rainfall. Did lower PoPs a bit
compared to previous forecasts, as the latest consensus from
the CAMS showers scattered coverage for most locations (as
opposed to likely or numerous). With less in the way of high
clouds around, it should be partly sunny and continued very
humid with highs 80-85. Fairly quiet once again Saturday night,
with showers and storms decreasing in coverage as we lose
daytime instability. Expect just a slight chance for a shower
overnight, under mostly cloudy skies with more patchy fog
around. Will be closely watching Henri, as it begins to approach
the southern New England or Long Island coast by daybreak
Sunday morning.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY/...
All eyes on Henri heading into the short term. Forecast track of
the center continues to trend westward, with an increasing
number of models and ensemble members ratcheting up the
potential rainfall impacts over parts of our CWA starting Sunday
afternoon and lasting into Monday or longer. The forecast track
of Henri beyond landfall is the more important question for us,
and confidence remains low. The further west Henri is able to
retrograde and interact/phase with the stalling upper level low,
the greater and longer- lasting the potential rainfall.
The area of highest concern is over the eastern half of the CWA,
in particular the Poconos/Catskills (and the latter`s western
foothills), essentially the headwaters of the Susquehanna and
Delaware Rivers. (Cautiously good news for hard-hit areas in
Steuben County).
For the time being, the heaviest QPF looks to stay just east of
our area, in line with the moderate and higher categories in
the WPC Day 3 Excessive Rainfall Outlook. This is largely based
on the official forecast track, which is already too close for
comfort, with the lower Hudson Valley within the "cone of
uncertainty".
The range of possibilities, illustrating the low confidence, can
be presented by 12Z ECMWF on the worst case extreme, and the 12Z
GFS as the best case extreme (for our CWA).
For the time being, we`re ramping up with a one-page briefing,
increasing PoPs Sunday afternoon through Monday Night,
particularly in the east. Deterministic QPF grids have also
increased modestly, but really are a useless tool for
communicating the true range of possibilities.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Any lingering showers in the east Tuesday should clear out
fairly early, as upper level ridging tries to nose in from the
southwest. Zonal flow will develop by Wednesday with weak
embedded disturbances bringing a slight chance of showers or a
thunderstorm late Wednesday. A more robust, but progressive
shortwave trough looks to bring a better chance for showers and
thunderstorms to the area on Thursday.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
8 PM Update
VFR conditions are expected to prevail the rest of this
evening areawide. Clouds have mainly lifted to mid level, with
sct to bkn conditions around 7-12k ft agl. Latest radar is
showing isolated to scattered rain showers around, but chances
for thunderstorms have diminished. These showers will continue
on and off overnight. Not enough coverage or probability to
include at any TAF site at this time. However, if one of these
showers impacts a terminal there could certainly be brief restrictions.
Heading into the overnight period, the latest model guidance
seems to be in good agreement for rather widespread fog and mist
to develop across the area...mainly between 21/06-12z. Best
chance to see the fog would likely be at the lower elevation,
valley terminals such as ELM and RME, but also included tempos
for MVFR vsby restrictions at all other TAF sites (except AVP).
There is a chance to see IFR restrictions at times just before
daybreak associated with the fog/stratus. Overall confidence in
this widespread fog/mist/low stratus forming is low to moderate.
Conditions are then forecast to improve rather quickly to VFR
after 12-15z Saturday morning areawide. There will be sct to
bkn mid level clouds around Saturday afternoon, with scattered
showers and isolated thunderstorms also developing.
Mainly light north-northwest winds less than 5 kts into the
evening hours. Winds become light and variable overnight into
early Saturday morning before becoming south-southeast still
under 5 kts later in the morning and afternoon.
Outlook...
Saturday night through Monday...occasional showers/thunderstorms
bringing restrictions mainly during the afternoon hours. Some
late night vsby restrictions due to valley fog, especially ELM.
Tuesday/Wednesday...Mainly VFR conditions expected. May see
early morning fog at ELM.
&&
.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...None.
&&
$$
SYNOPSIS...MJM
NEAR TERM...AJG/MJM
SHORT TERM...MPH
LONG TERM...MPH
AVIATION...MJM
Area Forecast Discussion
National Weather Service Dodge City KS
645 PM CDT Fri Aug 20 2021
...Updated Aviation Section...
.SHORT TERM...(This evening through Saturday)
Issued at 254 PM CDT Fri Aug 20 2021
A cold front was moving through central and southwest Kansas early
this afternoon and as of 2 pm, extended from around Hays to just
east of Dodge City to near Liberal. Per latest radar imagery, the
front has slowed down considerably across far southwest Kansas.
SPC analysis is showing an unstable airmass across the area with
SBCAPE values around 2500-3500 j/kg in areas from east of Dodge
City toward the Highway 281 corridor. Relatively drier air from
the Texas panhandle and far western Oklahoma spreading up into
the forecast areas has been keeping the CAPE values from spiking
quite so much. In addition, the best deep layer shear continues to
be farther northwest.
All of the CAMs show varying degrees of convective development across
southwest into south central Kansas this afternoon and evening with
the HRRR being the most aggressive. Visible satellite loops has
shown a line of elevated cumulus developing along the front from
near Liberal to southeast of Dodge City. With very warm mid level
temperatures (-4C at 500mb) over the area, it may be difficult to
get much convection to punch through and maintain through the late
afternoon hours. Still, with better low level convergence, we
can`t totally rule it out. If any storms do get going, a few
severe storms are possible with hail up to quarter size and strong
to damaging wind gusts. Will maintain the slight chance to chance
pops from the current forecast through this evening.
The front will continue to drop south and east overnight and is
forecast to extend from far southeast Kansas into the central Texas
Panhandle by Saturday morning. High temperatures on Saturday will
be several degrees cooler than today due to a slightly cooler
airmass easterly upslope winds during the day. The front is forecast
to lift back to the north during the day. The CAMs show showers
and thunderstorms developing along the front later Saturday afternoon
and evening. There is some question as to how much of this will
make it back into southwest/south central Kansas Saturday evening/night.
Will maintain some slight chance pops for that possibility.
.LONG TERM...(Saturday night through Friday)
Issued at 254 PM CDT Fri Aug 20 2021
After being shunted southward late this week into the weekend, the
extended period will see the upper level ridge rebuilding into an
east-west oriented upper high across the central and southern CONUS.
The ECMWF/GFS models show another less robust upper level wave moving
out of the northern Rockies into the northern Plains on Sunday. The
best chances for thunderstorms will be to the north of west central
and southwest Kansas as the frontal boundary associated with this
wave is progged to stay to the north of the forecast area.
Temperatures should be back up around 100 degrees across the forecast
area through the first half of next week. Additional waves crossing
the northern Plains could force a frontal boundary south into the
central Plains by around mid week but confidence in this is low
given the strength of the upper ridge.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 642 PM CDT Fri Aug 20 2021
This evening`s thunderstorm activity will remain east of the DDC,
GCK, HYS, and LBL terminals as the cold front continues to push
south and east across the southwest Kansas region. Behind the
front, prevailing wind will initially be north 10 to 15 knots,
weakening to below 10 knots overnight. The probability of post-
frontal low stratus development is very low, so the TAF will
remain VFR through this entire period. On Saturday, winds will
veer to the east through the day and increase to 12 to 17 knots.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 63 88 68 96 / 10 10 10 10
GCK 61 87 66 97 / 10 10 10 10
EHA 61 86 66 95 / 0 10 10 10
LBL 62 89 66 97 / 10 20 10 10
HYS 62 84 66 96 / 10 10 20 10
P28 70 92 70 98 / 30 20 20 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Gerard
LONG TERM...Gerard
AVIATION...Umscheid
Area Forecast Discussion
National Weather Service Des Moines IA
627 PM CDT Fri Aug 20 2021
.DISCUSSION.../Tonight through Friday/
Issued at 247 PM CDT Fri Aug 20 2021
Forecast Highlights:
-- Strong/severe storms with most likely timing after 6pm to 12am in
our forecast area
-- Saturday less humid and cooler
-- Humidity returns, strong to severe storms possible late
Sunday into Sunday evening, particularly western Iowa
-- Hot, humid early next week with storm chances throughout next
week
Details: Afternoon GOES-East upper level water vapor imagery shows
that the upper level trough has taken on a negative tilt as it
begins to lift northeastward over the Dakotas. Cloud debris from the
overnight elevated convection that moved into western Iowa has
diminished per visible satellite imagery with cumulus clouds forming
in streets parallel to the low level flow early this afternoon over
much of central Iowa.
An 85 to 90 knot, 250 mb jet as derived by GOES-East and RAP
analysis over the central Dakotas ahead of the trough will help to
continue to lift this trough northeastward away from the area. As a
result, the 6z/12z synoptic and CAM soundings showed weaker deep
layer shear in general along the front. Supplemental upper air
soundings at the request of the National Hurricane Center in support
of forecasting Tropical Storm Henri are also benefiting our
mesoanalysis. The KOAX 18z RAOB also showed the weaker 6km winds
around 30 knots with the 0-6km shear at 24 knots, similar to what
has been modeled. While surface based CAPE is over 3000 J/kg in the
warm sector ahead of the front per SPC mesoanalysis, storm
development in the warm sector away from the approaching cold front
is not expected to be robust with weak shear limiting the severe
potential. Further, the 18z KOAX RAOB showed the strength and depth
of the mid-level cap, which was between 850mb and 775mb. HRRR and
RAP forecast soundings show this cap weakening and adjusting the 18z
RAOB to the forecast high and associated dewpoint and attempting to
mix the boundary layer, inhibition should be minimal and storms will
be able to develop in the vicinity of the strong forcing of the
front. Convective initiation is already occurring over extreme
southeastern South Dakota per satellite and radar imagery.
Storm mode and as a result storm hazards will rely on the deep layer
shear. Latest SPC mesoanalysis shows 30 to 35 knots of 0-6km shear
right ahead of the boundary. HRRR sounding at YKN and SUX suggest
that the deep layer shear may top out at 40 knots right along the
front. The higher values of deep layer shear, if they exist and are
realized, could favor a few supercells. Compared to recent days, the
deep layer shear vector is not as orthogonal, but may allow for a
brief period of discrete cells. If a storm is able to maintain
isolation, then this would provide a window for a tornado and hail
threat perhaps as far east as our far western forecast area. As
storms grow upscale into multiple broken line segments and move into
our central Iowa forecast area, the hail threat will wane and the
damaging wind threat will increase. The 11z and now 16z and 17z
SSCRAM is also focusing the hazards on hail over western Iowa with
the wind threat from western into central Iowa. The greatest theta-e
differences per the NAM and GFS are over central into southern Iowa.
This is where the 12z HRRR and more recent runs continue to show
strong, gusty winds to around severe levels into this evening.
As the low level jet increases this evening, am fairly confident
that this will increase the 0-3km shear magnitude to 30+ knots, but
am less certain if this will be coincident or lagging behind the
storms. If the stronger 0-3km shear lags behind, then damaging wind
gusts would be the primary threat as just discussed. However, if the
shear remains with the boundary and the cold pool remains in
balance, storm segments that surge outward due to the strong, gusty
winds may help to orient the shear vector more favorably to the line
segment. This would increase the risk of QLCS tornadoes, especially
for any segment that bows and has sufficient 0-3km CAPE and shear.
With the exception of the NAM, models including the 12z HREF show
instability lowering this evening. Therefore, storms should be
trending down in their intensity as they move into central Iowa.
Confidence is higher that storms should be below severe limits
(could still have sub-severe gusty winds and lightning) as they move
into eastern Iowa and out of the state by sunrise Saturday.
As for the flash flooding threat, it continues to look extremely
low. There will be a narrow corridor of 2"+ precipitable water
values with very favorable warm cloud depths for efficient, heavy
rainfall. While the 850-300mb vectors are now somewhat parallel to
the front, the front itself will be progressive. Thus, this will
limit the residence time of heavy rainfall over a given area. 12z
HREF localized probability matched mean QPF shows a few bullseye of
3 to 4 inches over northern Iowa with 12z deterministic synoptic and
high resolutions models topping out with pockets of 2 to 3 inches.
Water issues such as ponding in low lying and poor drainage areas
may be possible in urban settings, but dry antecedent conditions
should fully mitigate any rural flash flooding concerns.
There will be about 24 hours of modest cold air advection over the
state on Saturday, which will deliver cooler and drier air.
Temperatures will be near or slightly below normal with highs in the
middle and upper 70s over northern Iowa to the low to middle 80s
over southern Iowa. Warm air advection will start to kick in on
Sunday bringing warmer and more humid air back into the state.
Moisture return will be greatest over western Iowa and eastern
Nebraska and South Dakota where dewpoints are expected to recover to
the upper 60s to middle 70s. This airmass will aid in an axis of
1500 J/kg instability over eastern Nebraska into eastern South
Dakota with deep shear over 35 knots aided by a shortwave trough
moving through the Dakotas. Storms will likely roll into western
Iowa after dark with the likely hazards being hail and strong, gusty
winds. On the large scale, there may be sufficient 0-3km CAPE and
shear, but will have to see how that aligns with the storms for any
QLCS tornado risk.
Thereafter, the mid-level ridge over the south central US will try
to build northward, but the zonal flow of the jet stream over the
northern US will limit its northward progression. With the flow
allowing for weak shortwaves to pass over a hot and humid airmass
across the region, expect there will be storm chances at times from
late Monday into late next week. 00z, 100 member WPC cluster
analysis does not show any dry clusters next week so with no strong
signal to go dry, will continue to let PoPs ride through the period
from initial guidance. As before, the highest chances will be late
in the afternoon into the overnight hours with activity generally at
a minimum in the morning hours. Beyond the storm chances, Monday
will be a sultry day with heat indices topping 100 degrees in
portions of southern Iowa with values just a bit lower on Tuesday.
&&
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 627 PM CDT Fri Aug 20 2021
Broken line of convection continues to affect northern sections
near KFOD and KMCW with potential for convection south yet aft
01z...moving east across forecast area through 05z. Southern area
of development somewhat less confident at this time and may need
to make some adjustments to TAFs at KDSM and KOTM if activity
fails to develop fully. Winds will drop aft 00z with additional
mixing/gusts aft 15z Sat most areas...gusts generally under
20kts. /rev
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Ansorge
AVIATION...REV
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1045 PM CDT Fri Aug 20 2021
.SHORT TERM...(This Evening through Saturday Night)
Issued at 247 PM CDT Fri Aug 20 2021
Morning and early afternoon cloud coverage as well as a weak cap has
led to less than ideal conditions for stronger storms to develop.
However, as the upper level wave and associated cold front has begun
to arrive the additional forcing has allowed for stronger
thunderstorms to develop across portions of the area. HREF ensemble
means show 1000-2500 J/kg of CAPE are available as well as 30-40
knots of bulk shear, leading to concerns for large hail and strong
winds. While the lapse rates are rather unimpressive, as the
previous forecast cycle mentioned half-dollar sized hail and gust up
to around 65 mph can be expected with the stronger storms.
High resolution guidance continues to suggest that these groups of
storms will merge into a linear feature by mid/late afternoon, at
which point the storms will have switched towards the primary threat
being strong winds. RAP is showing 500-1500 J/kg of DCAPE, further
indicating strong winds are likely with the later storms. While a
tornado or two cannot be ruled out, they are not very likely as the
0-3 km and 0-1 km bulk shear vectors are not fully perpendicular to
the motion of the line. Storms should be east of the I-29 corridor
by 8 pm and into central MN/IA by 10 pm, with the rest of the
evening expected to remain quiet. While fog cannot be ruled out
given the recent rainfall trapping moisture in the boundary layer,
winds look to remain mixy enough to leave fog out of the forecast at
this time.
Behind the ejecting upper level wave and associated surface low, a
weak surface high is expected to form under the area of upper level
ridging for Saturday. Combining the surface high pressure with the
unidirectional northeasterly wind profiles, winds will likely
remain on the breezy side on Saturday with gusts in the 20-25 mph
range. The northwesterly flow will also bring cooler air into the
region leading to afternoon temperatures in the mid 70s with
dewpoints largely in the 50s. As the aforementioned surface highs
slides eastwards across the area, winds will shift to be out of
the southeast allowing for the return of warmer air and surface
moisture to be brought to the region.
.LONG TERM...(Sunday through Friday)
Issued at 247 PM CDT Fri Aug 20 2021
The long-term forecast is initially focused on the severe weather
chances for Sunday, before transitioning to a quasi-zonal upper
level pattern with scattered chances for rain throughout the work
week. As apparent on the water vapor channels, the upper level wave
that will aid convective chances on Sunday can already be spotted
coming down the Pacific coast in the vicinity of Vancouver Island.
By Sunday morning, models have this wave lifting across the northern
Rockies and ejecting onto the northern Plains. At the surface, a low
pressure system will be moving across North Dakota, with associated
boundaries/fronts sagging southwards across South Dakota.
Throughout the morning hours and into the afternoon, the cold front
is expected to slowly shift eastwards, with warm and moist air being
brought into the region out ahead of it. This warm sector will lead
to a narrow corridor of 1000-2000 J/kg of CAPE with 40-60 knots of
bulk shear to work with. Warm air advection as well as the cold
front will likely serve as enough lift to allow thunderstorms to
form by the late morning, with additional lift coming as the main
wave catches up as we head into the afternoon hours. Could have a
couple different scenarios unfold including primarily scattered
showers due to the WAA and a weak cap leading to minimal severe
weather, but if the cap remains a bit stronger then the storms would
be able to remain a bit more isolated leading to chances for severe
storms. Will have to refine the messaging as the newer models come
in, but for now large hail as well as damaging winds and a tornado
are possible.
As the upper level flow becomes zonal-ish, Monday and Tuesday look
to be our warmest days with highs in the upper 80s and lower 90s
with a couple chances for rain. A surface low pressure looks to
bring a cold front down with it from Canada, leading to cooler
temperatures on Wednesday/Thursday with highs in the upper 70s and
lower 80s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1042 PM CDT Fri Aug 20 2021
VFR conditions expected through the TAF period. Northwesterly
winds will become gusty on Saturday morning and continue into the
afternoon. Winds then become light on Saturday evening.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&
$$
SHORT TERM...APT
LONG TERM...APT
AVIATION...JM
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
946 PM EDT Fri Aug 20 2021
.SYNOPSIS...
The threat for showers and thunderstorms is forecast to be
isolated today under this weak high pressure. A disturbance
will interact with an unstable airmass to keep a low chance for
precipitation Sunday.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Surface high pressure remains in place over the upper Ohio
Valley, with weak northerly flow over the ILN forecast area.
Just a few showers are persisting at this hour, with dry
conditions expected soon, and mostly clear skies expected
overnight.
No significant changes were made to the forecast overnight,
which includes the potential for fog. Compared to yesterday,
dewpoints are a little lower, there is much less of a signal for
widespread fog on recent HRRR runs and the 21Z SREF
probabilities. This suggests fog will largely be more limited to
river valleys tonight, with lighter visibility restrictions
elsewhere.
Previous discussion >
Weak high pressure is slowly drifting to the east with widely
scattered showers and thunderstorms occurring over west-central
Ohio and the Miami River Valley. Expecting this activity to
linger into the early evening before weakening.
Mostly clear skies are forecast once again tonight. Weak high
pressure will be further east of the region overnight so have
highlighted the best chances for fog across the Scioto and Ohio
River Valleys.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Fog impacts will improve by 9-10 am with the longest duration
expected for the lower Scioto Valley and northern Kentucky
counties.
For the afternoon, the local area is between TC Henri off the
Mid-Atlantic coast and a weak area of ascent the west. Leaned
drier than previous forecast package with temperatures in the
upper 80s and perhaps into the lower 90s.
Fog may once again be an issue Saturday morning with the lowest
visibility in local valleys/river valleys.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Weak front will move into the area on Sunday afternoon. There
may be enough forcing to generate some showers and thunderstorms
in western counties. Any activity will dissipate with loss of
heating. The boundary may make it further east overnight but
continue to weaken and eventually wash out on Monday.
Mid level ridge centered over the southern Plains will extend
into the Ohio Valley Monday and Tuesday. The eastern edge of the
ridge will then erode as weak troughing occurs along the
Appalachians. This will allow disturbances moving over the top
of the ridge to drop across the region. As a result there will
be a chance of showers and thunderstorms for mid to late week.
Above normal temperatures will persist, although readings may
start to moderate by the end of the period.
&&
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
This evening, a few showers are still floating around the area
near KCVG/KLUK/KDAY. At worst, some brief MVFR visibilities
could be possible, with no significant impacts appearing
possible. Dry conditions are expected after 02Z and for the rest
of the night.
Although not to the degree of last night, fog is possible again
tonight, with IFR/LIFR conditions possible at the typical
locations. At least some MVFR fog is possible at all six TAF
sites.
Winds will be light through the TAF period, generally 5 knots or
less.
Tomorrow, scattered cumulus clouds are expected, with only very
low precipitation chances -- far too low to include in the TAFs.
OUTLOOK...Thunderstorms are possible on Sunday afternoon, and
again on Tuesday and Wednesday afternoon.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...McGinnis
NEAR TERM...Hatzos/McGinnis
SHORT TERM...McGinnis
LONG TERM...
AVIATION...Hatzos
Area Forecast Discussion
National Weather Service Lincoln IL
912 PM CDT Fri Aug 20 2021
.SYNOPSIS...
Issued at 300 PM CDT Fri Aug 20 2021
A cold front will move through Illinois on Saturday and Saturday
evening, bringing scattered showers and thunderstorms later
tonight into Saturday evening. Dry and less humid weather is
expected Sunday behind this front. But the heat and humidity will
return during the work week, with heat indices over 100 possible
during the afternoon hours Monday through Wednesday.
&&
.UPDATE...
Issued at 910 PM CDT Fri Aug 20 2021
The cold front at 9 pm extended from western Iowa to eastern
Kansas, with slow but steady progress to the east. The latest runs
of the HRRR and RAP are both pointing toward a slower arrival of
the line of storms into our western counties, and also a more
complete dissipation of the line of showers/storms by 15z/10am.
There is enough agreement in the HREF/SREF guidance to trend in
that direction with the evening update. Have slowed down the onset
and advancement after midnight, and reduced the coverage of PoPs
during the morning into early afternoon. There could be a sizable
break in any rain in our CWA from 10 am to 3 or 4 pm, before the
front energizes during peak afternoon heating for areas east of
I-55. Even that coverage could be reduced with future updates,
based on the latest trends. Updated forecast info is already
available online.
&&
.SHORT TERM...(This evening through Saturday)
ISSUED AT 315 PM CDT Fri Aug 20 2021
Isolated convection has been staying out of central and se IL so
far today, focused more in southern IL into se MO and sw KY. Also
a few isolated showers/thunderstorms over central and ne IN into
western Ohio. Some subsidence over area with 587 dm 500 mb high
over IL and eastern WI keeping it dry and more stable despite the
warm and moist air mass with temps in the mid to upper 80s and
dewpoints in the upper 60s to mid 70s. Heat indices at mid
afternoon ranged from 89 to 96 over CWA.
1000 mb low pressure in east central ND has a cold front moving
into eastern SD/NE. Models have trended a bit slower with bringing
this cold front east into nw IL Sat morning. A broken band of
convection ahead of the cold front to push into the IL river
valley during overnight mainly after 2-3 am and get as far east as
I-55 by 12/7 am as it weakens. SPC day1 outlook keeps risk of
severe storms west of IL through tonight. Lows overnight mostly in
the lower 70s, with some upper 60s in east central IL and near the
IN border/Wabash river.
Convection to redevelop over eastern IL during Saturday afternoon
and diminishes during Sat evening as cold front moves through. SPC
day2 outlook does not have any risk of severe storms over IL
tomorrow due to weak wind shear around 25 kts or less. Have some
pockets of more unstable air in eastern IL Sat afternoon so could
be a few thunderstorms with gusty winds and locally heavy rains.
Highs Sat in the mid to upper 80s, warmest in southeast IL. Muggy
dewpoints in the 70s Sat gives afternoon heat indices in the 90s.
.LONG TERM...(Saturday night through Friday)
ISSUED AT 330 PM CDT Fri Aug 20 2021
Convection chances diminish over eastern IL during Sat evening
after sunset to 20-30%, then dry overnight Sat night and Sunday
with upper level ridge nosing back into IL. Getting a short break
from the high humidity as dewpoints slip into the mid to upper
60s nw CWA and lower 70s in southeast IL. Lows Sat night range
from low to mid 60s over the IL river valley, to around 70 in
southeast IL. Highs Sunday in the mid 80s central IL and upper
80s southeast IL. Lows Sunday night in the mid to upper 60s,
coolest from I-74 ne.
Another heat wave sets up over the area from Monday through
middle of next week as subtropical ridge takes hold. Some
disturbances/short waves ridging over top of the ridge could bring
period chances of showers/thunderstorms Monday through Friday. The
higher chances will be overnight Monday night into Tue especially
ne CWA. Highs Mon-Wed are in the lower 90s with dewpoints back in
the low to mid 70s, giving afternoon heat indices in upper 90s to
around 105F. Heat advisory may be needed during those afternoons
especially over southern CWA. The forecast builder brings a bit
cooler temps Thu/Fri with highs in the mid to upper 80s, with
se IL near 90 yet on Thu. Convection chances look more isolated on
Friday as upper level ridging nosing back toward IL.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 658 PM CDT Fri Aug 20 2021
The diurnal cumulus have dissipated with the approach of sunset, and
clear skies should prevail the rest of the evening. Fog potential
will be lower tonight than previous nights due to a steady southerly
wind ahead of an approaching cold front. The front will track to
near the IL/IA border by 12Z/7 am Sat and bring a broken band of
convection eastward into the IL river valley/PIA after 08Z and near
I-55 after 10Z and gradually weaken as it moves into eastern IL
during Sat morning. Have VCTS for the thunderstorm chances for a few
hours and then VCSH with lowering ceilings to MVFR from I-55 Sat
morning. SE winds will remain in the 5-7kt range tonight, then
become south to SSW at 7-10 kts Sat.
A reduction in storm and rain chances will develop by mid-day, but
additional storms may re-develop mid to late afternoon on
Saturday, especially east of I-55.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Shimon
SYNOPSIS...07
SHORT TERM...07
LONG TERM...07
AVIATION...Shimon
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1003 PM CDT Fri Aug 20 2021
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
Rest of tonight:
The region remains under influence of weakening mid-level ridge
axis to the W over ArkLaTex through the Ozarks with more NW flow
over our region. Weaker ridging extends well S across the Gulf of
Mexico & into the subtropical Atlantic, which is guiding both
Grace & Henri on each track into the SW Gulf & N along the
Atlantic seaboard, respectively. Deep trough & front extends off
to the N in N Plains & an MCS should drift SE through the
overnight hours. Due to lingering deep soupy tropical moisture,
some rain & storms remain possible tonight but most potential
will be later tonight. This is supported by most CAM guidance so
cut rain chances quite a bit further W. Isolated coverage will be
along & NE of a line from Greenville to Jackson to Quitman with
best scattered rain & storm coverage from Grenada to Meridian &
NE into the Golden Triangle. Recent HRRR runs support this idea &
after 3-4AM & through daybreak coverage increasing. Low temps
will be above climo in the low-mid 70s. Updates are out. /DC/
Prior discussion below:
This afternoon through Saturday: convective rainfall is most
prevalent over eastern portions of the ArkLaMiss region with high
precipitable water values (> 2.3 inches) supporting locally heavy
rainfall. Coverage shouldn`t be quite as great late this afternoon
into the early evening as it was yesterday with the subtropical
ridge building over the forecast area, and expect activity to
diminish with sunset, although some shower chances will linger
overnight as has been the case mainly over northern portions of
the area.
For Saturday, a marginal severe weather threat appears to be
setting up for the afternoon. A weak perturbation in the low/mid
levels is expected to enhance the flow and potentially support the
development of a mesoscale convective system that CAM guidance
suggest could affect northern/eastern portions of the forecast
area by late morning and into the afternoon. In the least, would
expect a few multicell line segments to develop and impact this
area, but ridging should keep western/southern portions of the
area more limited in terms of convective coverage. Given the very
buoyant airmass, organized storms and a cold pool could lead
quickly to a strong/svr wind threat, especially where/if SE low
level wind vectors become more favorably oriented with cold pool,
hence a marginal risk for severe storms has been included in the
HWO for northern/eastern portions of the area. Southwest portions
of the marginal risk area (including the Jackson metro area) are
more conditional and based more on a stronger cold pool
developing.
Otherwise, heat is still an increasing threat as we go through the
weekend. For Saturday, we`ll see heat indices reach heat advisory
criteria over mainly the upper Delta region and have issued an
advisory for there. This is generally in line with the prior HWO
issuances of an elevated threat area. /EC/
Tomorrow night through Friday:
The forecast period starts off tomorrow night with an anomalously
strong sub-tropical ridge centered over the ArkLaTex and into the
Lower Mississippi Valley. On the northeastern periphery of the
ridge, a weak impulse embedded in northwesterly flow will support
isolated to scattered showers and thunderstorms mainly across
eastern Mississippi on Sunday. The main focus, however, will be
oppressive heat as rising heights and warming low-level temperatures
will support afternoon highs in the mid to upper 90s. These
temperatures in concert with a very humid airmass will result in
dangerous heat indices of 106-115 degrees with the highest readings
expected across the Delta. The upper ridge is progged to persist
across the region Monday and Tuesday as well with temperatures
soaring into the upper 90s each day. A few readings at or near the
century mark will be possible, especially along and west of the
Mississippi River. Heat indices will continue to range from 106-115
degrees across the same areas with dangerous heat stress continuing.
As such, have introduced a significant area for dangerous heat in
the HWO/graphics for the Delta and a combination of excessive heat
warning and heat advisory products will likely be needed. Placement
of the upper ridge will shunt precipitation south for Monday and
Tuesday with the greatest chance for afternoon showers and
thunderstorms confined to the Pine Belt as seabreeze convection
penetrates inland.
By mid to late week, the stout upper ridge is progged to retrograde
west into the Southern Plains with heights beginning to lower over
the Lower Mississippi Valley. This will allow for greater coverage
of diurnally driven showers and storms across much of the area as
well as slightly cooler temperatures in the low to mid 90s. Some
heat stress concerns may linger into Wednesday and another heat
advisory may be needed, but will handle that separately as it gets
closer. Heat indices Thursday and Friday will range from 100-105
degrees, which while still hot, will not be as oppressive as the
heat earlier in the week. /TW/
&&
.AVIATION...
00Z TAF discussion:
VFR conditions are mostly prevailing this evening with some MVFR
to IFR concerns where there is rain and storms. These should
continue to diminish or move out of the region through the
evening. MVFR stratus and/or fog will be possible overnight prior
to daybreak before a return to VFR conditions should occur
tomorrow. Additional showers and storms will occur mainly across
the east and northeast tomorrow. /28/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 75 92 74 96 / 16 38 17 40
Meridian 72 89 72 94 / 17 62 27 51
Vicksburg 75 95 75 97 / 11 17 7 26
Hattiesburg 74 94 74 96 / 16 22 15 53
Natchez 73 93 74 96 / 3 6 2 26
Greenville 76 92 74 96 / 14 36 18 25
Greenwood 75 90 74 95 / 19 66 28 30
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory from 10 AM to 7 PM CDT Saturday for MSZ018-019-025-
034-035-040-041-047.
LA...Heat Advisory from 10 AM to 7 PM CDT Saturday for LAZ007>009-015-
016.
AR...Heat Advisory from 10 AM to 7 PM CDT Saturday for ARZ074-075.
&&
$$
DC/28
Area Forecast Discussion
National Weather Service Key West FL
1020 PM EDT Fri Aug 20 2021
.DISCUSSION...
The BYX WSR-88D is free from rain echoes this evening, with the
evening sounding largely maintaining the total column moisture
from this morning. There was a slight vertical redistribition of
the moisture with the 850 mb level drying and the 700 mb level
slightly moistening. Buoyancy was similar to this morning,
although boundaries are scarce outside of any residuals from this
afternoon`s wet cloud line across the lower Keys. UWISC-CIMMS
Mimic precipitable water estimates indicated values near 1.9
inches traversing slowly westward over the Straits, and it is a
matter time before convective processes resume during the early
morning hours. HRRR guidance indicated a later onset near sunrise
whereas experimental Caribbean-domain HRRR indicated more generous
development initiating an hour or two before sunrise.
While earlier tempted to reduce rain chances, believe the onset
will likely be simply closer to the end of the overnight period.
No change to the light east to southeast winds over the islands.
&&
.MARINE...
There are no watches, warnings, or advisories currently in effect
for the coastal waters of the Florida Keys. For overnight, light
east to southeast breezes are expected. Waters will begin mostly
rain-free, with showers and possibly a few thunderstorms as well
developing along short towering cumulus lines evolving during the
early morning hours. Continuing with the previous synopsis, high
pressure extending from the Western Atlantic across the Florida
Peninsula will maintain gentle to moderate east to southeast
breezes Saturday through Monday. Breezes will freshen Monday
night and Tuesday as the Bermuda high pressure system strengthens.
&&
.AVIATION...
VFR conditions will prevail at the island terminals. Surface winds
will be light out of the east through the overnight.
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...JR
Aviation/Nowcasts....11
Data Acquisition.....KR
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Area Forecast Discussion
National Weather Service Newport/Morehead City NC
909 PM EDT Fri Aug 20 2021
.SYNOPSIS...
High pressure will continue offshore with weak troughing nearby
into the weekend. Tropical Cyclone Henri will pass offshore
tonight and tomorrow, shifting the surface trough axis near the
coast Sunday through much of next week.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 9 PM Fri...Most of the strongest convection has waned
this evening with much of the area having been worked over from
earlier storms but scattered shower and thunderstorm development
will be possible much of the overnight as favorable upper level
dynamics across ENC continues ahead of a vort max pivoting
through the upper level cut-off low centered over OH/WV/western
PA. Training of storms brought significant rainfall amounts
across portions of the area with some locations receiving 2-4
inches and localized amounts up to 6 inches which will allow
for widespread fog and stratus overnight. Forecast update mainly
caputures PoP and temp trends this evening.
Previous discussion...Upper air analysis this afternoon shows
broad troughing continuing to sit over much of the eastern
CONUS, and this is expected to slowly meander south and east
through the short term as it interacts with distant TC Henri. At
the surface, a weak frontal boundary continues to linger
roughly along Highway 17 this afternoon, most clearly delineated
by both temperature and instability fields. Convection has
quickly fired across the Albemarle Peninsula and the Northern
Outer Banks, and satellite/radar trends indicate this will
continue to fill to the south through the next hour.
Expect convection to continue building both south along the
frontal boundary, and inland through the early evening as
outflow from existing activity spreads west into an increasingly
unstable airmass characterized by SBCAPE of 3500-4500 J/kg. The
airmass is highly favorable for storms capable of significant
rainfall with PWATs close to 2.30" and low and mid level RHs of
80-90%. With storms pinned along a frontal boundary and storm
motions generally around 5 kt or less, training storms also
remain a concern. Additionally, RAP soundings have also hinted
at effective shear climbing to 30-35 kt late this afternoon with
the development of a LLJ over the region. This could lead to a
low- end severe threat with the potential for damaging wind
gusts. A waterspout or weak tornado remains possible immediately
along the frontal boundary.
Convective coverage slowly wanes tonight although most hi-res
guidance hints at some isolated periodic showers inland
overnight, likely developing along remnant outflow boundaries.
Otherwise, with freshly saturated soils expected low stratus is
likely to develop especially west of Highway 17. With light to
calm winds would not be surprised to see stratus lower to the
surface, restricting visibilities in the early morning.
Low temperatures remain similar to the past several, sitting in
the low 70s, mid to upper 70s along the coast.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
As of 350 PM Fri...Upper troughing will linger over the region
tomorrow with surface front decaying. Main forecast challenge
will be convective coverage tomorrow, as drier mid-level air
will quickly be advected into the area as the trough interacts
with Henri and PWATs drop to around 1.5" inland. Deeper moisture
will likely remain in place along the Outer Banks and the
Albemarle Sound and show highest PoPs here, although still can`t
rule out an odd shower or storm well inland as well despite
more hostile conditions. Highers slightly cooler than today, but
still in the mid to upper 80s.
Along the coast, high surf courtesy of TC Henri will create
dangerous beach conditions along the Outer Banks from Cape
Lookout to Oregon Inlet...see the Tides/Coastal Flooding section
for more details.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
As of 330 AM Fri...Troughing over the area may bring unsettled
weather Saturday as Henri passes well off the coast. Coastal
areas remain unsettled through much of next week, while inland
areas return to a more seasonal pattern starting Sunday.
Sunday through late week...Closed upper low over the Mid-
Atlantic coast as the the surface trough axis in the wake of
Henri slides over ENC, where it will remain into late week. By
mid-week, the upper low is absorbed into the background flow
over New England and a general weakness persists overhead.
A fairly persistent forecast through the period, with the trough
axis linger nearby keeping week flow locally and much stronger
low level moisture advection expected to remain offshore.
Isolated to scattered shower activity could be more persistent
along the coast, while a more seasonable/diurnal precip pattern
is expected inland. Temps generally near to a few degrees above
normal through the period.
&&
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
SHORT TERM /through Saturday/...
As of 8 PM Fri...Widespread convection has waned early this
evening but isolated to scattered showers and storms possible
trough the overnight bringing reduced cigs/vsbys. Significant
rainfall amounts occured over much of the region leaving plenty
of moisture in the lower levels and expect LIFR/IFR fog and
stratus to develop across much of the region after midnight,
which should lift to VFR around mid-day Sat. Pred VFR conditions
expected Sat afternoon with only isolated showers or storms
possible across much of the area, though far eastern rtes may
have a better coverage of showers and storms where outer bands
of TC Henri may impact.
LONG TERM /Saturday night through Tuesday/...
As of 345 AM Fri...Isolated to scattered showers and storms are
possible early afternoon into early next week, bringing the
potential for brief, localized flight restrictions.
Overnight/early morning fog and/or low stratus will also be
possible.
&&
.MARINE...
SHORT TERM /Tonight and Saturday/...
As of 350 PM Fri...Conditions deteriorating over the offshore
waters this afternoon as swell from TC Henri continues to build.
Expect seas to peak at 8-9 feet especially for central waters,
before beginning to ebb starting tomorrow afternoon. Local NWPS
guidance likely reducing seas too quickly, as is typical with
tropical influences, and SCA conditions are likely to continue
to the end of the period.
Despite rough seas, winds are not of consequence with SE flow
backing northerly at 10-15 kt as Henri passes well to our east.
LONG TERM /Saturday night through Tuesday/...
As of 355 PM Fri...Relatively quiet conditions expected across
the waters in the long term with winds returning to
predominantly a SW regime through the period. Slightly stronger
winds Sunday into Monday of 15-20 kt will likely keep seas at
4-5 feet for outer waters and can`t completely rule out a 6
footer or two. Otherwise, no SCA potential on the horizon.
&&
.TIDES/COASTAL FLOODING...
As of 4 PM Fri...TC Henri is expected pass offshore as a
Hurricane tomorrow. Dangerous surf conditions and elevated rip
current risk will continue through the weekend. A High Surf
Advisory has been issued from Cape Lookout north to Oregon
Inlet, starting overnight tonight and running to Saturday
evening for waves of 6-10 feet in the surf zone. Additionally,
elevated astronomical tides and the increased swell could
combine to bring minor beach erosion and the potential for
overwash for portions of beach with very vulnerable dune
structures with the early evening high tide cycles Sat and Sun.
&&
.MHX WATCHES/WARNINGS/ADVISORIES...
NC...Beach Hazards Statement through Saturday evening for NCZ195-
196-199-203>205.
High Surf Advisory from 2 AM to 8 PM EDT Saturday for NCZ196-
204-205.
MARINE...Small Craft Advisory until 11 PM EDT Saturday for AMZ150-152-
154.
Small Craft Advisory until 8 PM EDT Saturday for AMZ156-158.
&&
$$
SYNOPSIS...MHX
NEAR TERM...SK/MS
SHORT TERM...MS
LONG TERM...CQD/CB
AVIATION...SK/CB/MS
MARINE...CB/MS
TIDES/COASTAL FLOODING...MHX
Area Forecast Discussion
National Weather Service Marquette MI
757 PM EDT Fri Aug 20 2021
.SHORT TERM...(This evening through Saturday)
Issued at 327 PM EDT FRI AUG 20 2021
Currently, we are looking almost like a complete repeat of
yesterday. Satellite imagery shows diurnal cu popping up in the U.P.
this afternoon as a dry high pressure ridge slowly makes its way
eastward. Some areas in the elevated terrain near Lake Superior (and
near southern Houghton County) are already around 90F! The only
saving graces right now is that RHs are around 40% in those areas
this afternoon and there is a light south/southwesterly breeze
across most of the area. Some light haze can still be seen across
the area, particularly in the east (as seen in the vertically
integrated smoke product in the HRRR smoke model). This haze should
slowly leave the area tonight as a cold front approaches from the
west.
Tonight, expect temperatures to bottom out near the 60s across the
area, as some cloud cover associated with the cold front should
start rolling into the western CWA late. As the front approaches,
expect southerly winds to pick up from west to east. These winds
should bring some breezy conditions across the area ahead of the
cold front tonight and Saturday. Not expecting the rainfall
associated with the cold front to arrive in the far west until late
tonight. Given that only the NAM12km was showing some CAPE along the
frontal boundary during the overnight and early morning hours,
decided to cap thunder chances to slight until late Saturday
morning.
As the front progs eastward throughout the day Saturday, expect
cooler temperatures (mainly upper 70s) in the west behind the front,
whereas the far east (near Newberry) could see still see
temperatures approach the mid-80s. Could still see some pockets of
low 80s along the downslope areas near Lake Superior, as the
downslope of southerly winds could raise temperatures to get over
80. Also, could see the low-80s in the south central too Saturday,
as the front isn`t expected to arrive until the afternoon.
Thunderstorm chances improve throughout the day Saturday, as some
diurnal heating ahead of the cold front should increase instability
in central and eastern Upper MI. Not expecting severe wx, as the
front should be dying as it moves east; while MUCAPEs look modest
(around 1000-1500 J/kg) and bulk shear looks marginal for severe wx
(around 30 knots at most spots near the frontal boundary), because
the front is dying, the forcing mechanism to produce convection
should weaken with time. Therefore, while I think convection is a
definite possibility, I`m doubtful that the modest instability and
marginal bulk shear will be enough to overcome the loss of forcing
in the cold front to produce severe wx. The better forcing for
convection is expected north of us in northern Ontario, as the low
associated with this cold front lifts northeast towards Hudson Bay.
Thinking we will see more breezy conditions behind the cold front
Saturday, particularly in the Keweenaw Peninsula, as significant
height rises and temperature advection is expected; the Keweenaw
could see some wind gusts over 35 mph late tomorrow afternoon! The
wind direction behind the front is expected to be westerly.
.LONG TERM...(Saturday night through Friday)
Issued at 341 PM EDT FRI AUG 20 2021
Through the extended fcst period, models indicate mean troughing
over western Canada, and at times over the western CONUS, as a
series of shortwaves eject eastward across the northern CONUS and
Upper Great Lakes region in a progressive flow through next week.
Based on dynamics and available moisture, it looks like the more
promising chances for widespread showers would not be until mid to
late next week. Temperatures will fluctuate from near to above
normal through much of the period.
Beginning Saturday night into Sunday, models indicate any remaining
showers ending in the evening over the eastern portion of the cwa,
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 and dew points in
the upper 40s to mid 50s. Waves generated from fairly gusty nw-n
winds behind the front will likely warrant a high swim risk for
Alger County on Sunday.
The next shortwave moving across the Northern Plains on Sunday will
weaken as it lifts into northern Ontario by Monday morning. Models
show a weaker pcpn signal with this weakening wave compared to the
wave on Saturday. Even though GFS soundings indicate MLCAPE values
increasing to 500-1000j/kg Mon ahead of the front, warm nose of
nearly 17C temps aloft and fairly significant CIN may prohibit
convective development on Mon across much of the area. In the end,
the better chc of pcpn with this wave looks to be late Sun
night/early Mon over the w in association with an approaching, but
weakening 30 kt low-level jet. Otherwise, nothing more than low
chc/schc pops are warranted late Sun night/Mon. Max temps will rise
back into the lower to mid 80s most locations on Monday and Tuesday.
Latest models indicating perhaps a better signal for showers/t-
storms with the next shortwave due in late Tue into Wed. Trends
indicate better shortwave dynamics and stronger WAA/moisture
transport ahead of the system. With MUCAPE values approaching 1000-
1500 j/kg and deep layer shear 40-50 knots there certainly could be
some strong to marginally severe storms associated with this system.
High pressure building in behind this system should result in dry
and cooler conditions on Thursday.
Models certainly differ on the timing/strength details but there
does appear to be a pretty consistent signal that a broader, deeper
trough will dig in from the Northern Plains late next week/weekend
bringing more opportunities for rainfall.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 745 PM EDT FRI AUG 20 2021
A line of showers and thunderstorms associated with a frontal
boundary will make their way across Upper Michigan overnight into
tomorrow. However, there is still ample uncertainty in some of the
details, such as whether they`ll directly impact the terminals,
whether they`ll contain lightning, and if they do hold together,
their strength. Based on the latest analysis, have gone with VCTS
mention at all three terminals since they likely won`t reach the
western-most terminal of KIWD until after the next TAF issuance.
Therefore, should have a much better handle on how the storms are
fairing, particularly with the loss of daytime heating, and can
determine potential TEMPO groups, TS/CB mention, etc. With a very
dry airmass on either side of the convection, clouds/ceilings are
expected to be minimal outside of when the showers/storms are in
the respective terminal`s vicinity.
Higher confidence exists in gusty winds impacting all three
terminals for the majority of this TAF period, especially at and
around KCMX. LLWS is to be expected as well, particularly at KIWD
and KCMX, with a bit more of a question on it occurring at KSAW
(within mentionable criteria). Southerly winds at the start will
have a much more westerly component by the end of the period,
particularly at KIWD and KCMX as the front passes through.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 327 PM EDT FRI AUG 20 2021
Winds should remain 20 knots or less until this evening. As a cold
front approaches the lake tonight, expect southerly winds to
increase to 20 to 30 knots ahead of the cold front. As the cold
front moves through Saturday, expect the southerly winds to weaken
ahead of the front and for the westerly winds behind the front to
strengthen to 20 to 30 knots. Some westerly gale force gusts up to
35 knots are possible behind the cold front in the western and
central lake Saturday afternoon and evening. As the winds become
northwesterly Saturday evening, expect wind speeds to diminish; by
Sunday morning the winds should be 20 knots or less. The winds
should remain around 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 Nashville TN
924 PM CDT Fri Aug 20 2021
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
00Z models starting to trickle in this evening, and are showing
the same features for the overnight hours as before. Upper
shortwave will allow for subtle lift overnight for an already
unstable atmosphere, and with PWAT values of 2-2.5 inches, weak
shear, and sustaining instability, flash flood threat remains.
This is especially true in the watch area southwest of Nashville
where MRMS estimates 2-4 inches have fallen over the past few days
and even some areas creeping towards 5 inches. The HRRR has been
slowly trending further east with the heavy rain, and may creep in
towards Davidson County, but other CAMs holding strong with the
main precip axis from Houston County down through
Lawrence/Giles/Marshall. However, areas west of the Plateau and
outside the watch still need to remain weather aware this evening
since any slight shifts in the upper wave, boundary, moisture
axis, etc may result in the heavy rain and flooding potential
moving eastward. Current runs that have come in still suggest
watch area is valid, but remain weather aware tonight!
The NAM/GFS have trended with less rainfall, but obviously not as
high res as CAMs. The NAMNest 00Z run still shows a very heavy
rain axis from southern Humphreys County through Lawrence/Giles,
and similar to what it showed at 12Z/18Z. Current obs with
dewpoints in the mid 70s and even upper 70s west of the TN River
suggest plenty of moisture with little needed to trigger showers
and storms that will be very efficient rain producers thanks to
high freezing levels near 15-16kft, PWATs over 2 inches, and
MLCAPE around 1000 J/kg. Rainfall rates of 2-3 inches per hour
will be possible, and 2 to 4 inches of rain with localized higher
amounts are not out of the question. Should the heavier rain
totals travel over already saturated areas such as
Wayne/Lawrence/Giles/Marshall, flash flooding will occur quickly.
Make sure you have multiple ways to receive warnings tonight,
even if you are outside of the watch as this atmosphere is going
to have no issue producing heavy rainfall west of the Plateau
should showers/storms develop further east outside of the watch.
Heavy rain threat should start to weaken in the early afternoon
Saturday.
&&
.AVIATION...
00Z TAF DISCUSSION.
Chances for showers and thunderstorms will have a short break
later this evening, but return overnight and mainly be in the
vicinity of KBNA/KMQY/KCKV. Fog will also be possible outside of
showers, especially at KCSV where IFR and even LIFR fog will be
possible. MVFR cigs or lower may impact terminals from around
sunrise through the morning hours before becoming VFR in the
afternoon, with additional chances for showers and storms across
the region.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 1 AM CDT Saturday through Saturday
afternoon for Bedford-Cheatham-Dickson-Giles-Hickman-Houston-
Humphreys-Lawrence-Lewis-Marshall-Maury-Montgomery-Perry-Stewart-
Wayne-Williamson.
&&
$$
DISCUSSION......Barnwell
AVIATION........Barnwell
Area Forecast Discussion
National Weather Service Pocatello ID
158 PM MDT Fri Aug 20 2021
.SHORT TERM...Today through Sunday night. Weak ridging is in
place today with overall dry northwest flow aloft. Isolated
showers and thunderstorms are possible over our northern areas,
mainly the Montana Divide, this afternoon with residual moisture
and instability.
Saturday will be another active day. The next disturbance/trough
moves through on Saturday. Ahead of this system there will be
moderate southwest flow bringing breezy to moderate winds. The
HRRR smoke model shows widespread smoke from California being
drawn back into the area ahead of this next system. Saturday
morning moisture starts in the northern Central mountains and
then spreads across the area into the Southeast Highlands by late
afternoon into the early evening. Expect scattered showers and
thunderstorms and breezy to moderate winds as this system moves
through the area. Red flag warnings are in place over our western
areas for scattered thunderstorms. There is a marginal risk in the
excessive rainfall outlook by WPC for the Southeast Highlands. In
the Bear Lake region expect around 0.50 of rain, with locally
higher amounts. Additionally, there is a marginal risk in the SPC
convective outlook over the Southeast Highlands. Thunderstorms in
this region could be severe. The biggest threat would be very
strong winds of 50 to 60 mph from any thunderstorms in this area.
By Sunday morning expect drier conditions with breezy northwest
flow building in. By Sunday afternoon, the flow aloft still
remains breezy but becomes more westerly to southwesterly. This
direction would continue to support bringing in smoke from
California and Oregon.
Expect temperatures 5 to 10 degrees below normal today and
Saturday before warming to slightly below normal by Sunday.
Wyatt
&&
.LONG TERM...Monday through next Friday. The models and cluster
forecasts continue to show a lingering trough across our area
Monday. This will help produce isolated showers and thunderstorms
along the Montana and Wyoming borders. We are still looking for dry
conditions most likely next week, however trends mostly show the
stronger ridge initially forecast to not materialize. There are a
few in the cluster forecast that show this, but the signal is for
some form of a trough remaining across the region. The strength and
any potential passing of a low through Idaho is not something we can
pin down at the moment. With this in mind, while it will still warm
up...we may not get as warm later next week as we originally
thought. The Blend of Models also really doesn`t have much, if
anything, for showers and storms as well. This fits the trend for
now and we will let that ride.
Keyes
&&
.AVIATION...We will are still expecting another round of showers and
thunderstorms through this evening, mainly impacting border areas
including DIJ. While VFR will be the main TA forecast, we are
already seeing and may with other convection see MVFR/IFR weather.
Showers and thunderstorms will be on the increase Saturday from west
to east. Stronger showers and storms may produce MVFR/IFR weather
and gusty winds over 30kts.
Keyes
&&
.FIRE WEATHER...We are looking for showers and isolated storms
through this evening across the central mountains, 411, and border
areas of 413. Some rainfall is expected but gusty winds are possible
with stronger activity that forms. Showers and thunderstorms will
increase from west to east Saturday as the next low crosses the
state. It looks like by afternoon scattered storms should develop
across the higher elevations, especially across the southeast corner
and western side of our central mountains. Through tomorrow evening,
scattered thunderstorms are possible over pretty much all of central
and eastern Idaho. Wetting rains are more likely across the central
mountains and also Zones 411 and 413. While not as high, a pretty
good chance of wetting rains is forecast across the Snake Plain.
However, for Zones 422/425/427...wetting rains are much less likely.
For those areas, we have issued a RED FLAG WARNING for tomorrow
afternoon and evening. Gusty winds over 35mph are possible with some
of those storms as well. Showers and storms will end west to east
Sunday, with lingering showers and isolated storms mainly around
Island Park and Driggs by afternoon. Another quick round of showers
and isolated storms are possible Monday afternoon and evening across
411 and the Wyoming border area of 413. Beyond that, the trend of a
stronger ridge over Idaho is quickly fading. It appears some sort of
"trough" will remain over our area. This will give us slightly
cooler temperatures than previously forecast. The forecast remains
dry for now, but we will need to watch and see if any particular
storm passing through is enough for showers and storms.
Keyes
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon Saturday to midnight MDT Saturday
night for IDZ422-425-427.
&&
$$
Area Forecast Discussion
National Weather Service San Diego CA
853 PM PDT Fri Aug 20 2021
.SYNOPSIS...
Increased onshore flow and a deep marine layer will continue
through Saturday. Areas of drizzle are possible along the coast
Saturday morning. A warming trend is expected to start Sunday and
will continue through at least Friday. As conditions get warmer,
the marine layer will become shallower with night and morning low
clouds not reaching as far inland.
&&
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING
ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN
BERNARDINO COUNTIES...
UPDATE...
Low clouds never really cleared much in the coastal areas and
western valleys of San Diego County, and have now begun to spread
into the inland valleys and north into Orange County and the far
southern part of the Inland Empire. Low clouds will fill in west
of the mountains overnight. The 00Z KNKX sounding shows the marine
inversion based near 3200 ft MSL, down from around 4000 ft MSL
this morning. An upper level low moving inland to the north
overnight should deepen it up again slightly. Only forecast update
this evening was to adjust smoke forecast for Sat/Sun based on
latest HRRR runs.
PREVIOUS DISCUSSION...
Key Points:
*Cooler conditions through Saturday, with drizzle possible in San
Diego coastal areas Saturday morning.
*Warming trend expected Sunday through Friday, with temperatures
peaking Thursday and Friday.
*Hazy conditions for portions of Southern California through
Saturday due to smoke from fires in Northern California.
*Increased risk of strong rip currents through Saturday (see beaches
discussion).
HRRR smoke model outputs are showing more substantial smoke from
fires in northern California extending into portions of southern
California into Saturday. The greater values of vertically
integrated smoke will extend into Los Angeles County, portions of
the coastal waters, and portions of the High Desert.
A low pressure system moving through the Pacific Northwest tonight
into Saturday will deepen the marine layer and result in widespread
below average high temperatures on Saturday. The increase in onshore
flow and deepened marine layer combined with a passing vorticity
maximum tonight into Saturday morning could produce some light
drizzle in coastal locations. ECMWF Extreme Forecast Index is
showing portions of the coast, mainly southern San Diego County in
the 0.5 to 0.6 range for QPF on Saturday. If any drizzle were to
fall, only small accumulations of less than a tenth of an inch are
expected.
A ridge of high pressure will begin to build in from the east
Sunday, starting a warming trend. Temperatures on Sunday and Monday
will remain below average but will warm a few degrees each day.
Conditions will reach near average by mid-week, with temperatures
becoming 5 to 10 degrees above average by Thursday and Friday. After
Friday, model spread increases in regards to the placement of a low
pressure system off the California coast. There is one model cluster
that would be warmer for that weekend than Thursday/Friday with two
cooler. The deterministic NBM shows very slight cooling for Saturday
and Sunday.
&&
.AVIATION...
210315Z...Coast/Valleys...Low clouds already covering
San Diego County will gradually fill the entire coastal basin by
10Z. Bases are 2000-2500 feet MSL with tops to 3500 feet. Vis
reduced between those altitudes. -DZ possible around KSAN from 12Z-
16Z. Clearing to the coast Saturday between 17-20Z, but some areas
mainly in San Diego County will not clear fully or for very long.
Low clouds to redevelop at similar levels after 02Z Saturday night.
Mountains/Deserts...SCT locally BKN clouds at 9000 feet will clear
tonight. Mostly clear Saturday.
&&
.MARINE...
No hazardous marine conditions through Wednesday.
&&
.BEACHES...
A southwest swell producing elevated surf and strong rip currents in
Orange County today will slowly diminish this weekend. See the Beach
Hazards Statement and the Surf Zone Forecast for details.
Evening high tides of up to 6.6 feet combined with the above average
surf may produce beach erosion and minor tidal overflow at low-lying
beach areas, boardwalks, and parking lots.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Saturday evening for Orange
County Coastal Areas.
PZ...NONE.
&&
$$
PUBLIC...SS/CO
AVIATION/MARINE/BEACHES...MM
Area Forecast Discussion
National Weather Service Topeka KS
546 PM CDT Fri Aug 20 2021
.MESOSCALE DISCUSSION...
Issued at 546 PM CDT Fri Aug 20 2021
2230Z surface analysis showed the front from near Hebron, NE to
just west of Salina, KS. Thunderstorms have developed along this
boundary with some isolated wind and hail reports already. Radar
shows a fine line from near Marysville through Manhattan and
central Morris CO. This could be the prefrontal trough or a sudo
dryline with higher dewpoints to the east. There is some concern
that boundary layer moisture and instability may see a increase to
the east of this feature allowing storms to intensify. Surface
winds also remain slightly backed to the south southeast east of
the fine line features. So any discrete storms will have a better
chance for an organized updraft and more intense severe weather.
Right now they have been a little pulse and having trouble
sustaining an updraft. The expectation as the evening progresses is
for storms to congeal into lines and clusters with a damaging
wind threat emerging. Locally heavy rainfall could also cause some
problems.
&&
.DISCUSSION...
Issued at 317 PM CDT Fri Aug 20 2021
The main concern for weather in the short-term is a negatively-
tilted shortwave trough that will be moving through the upper
Midwest this evening into Saturday morning. This wave will bring the
chance for a line of thunderstorms to form along the boundary in
northeast KS in the early to late evening hours.
At 20Z, mid-level water vapor imagery shows the trough moving into
the northern Plains. An associated weak surface low will slowly
propagate northeast along the trough axis bringing a cold front
into the forecast area. Warm sector CAPE values are ranging from
3500 to 4500 J/kg as diurnal heating continues. A 10-15 knot
surface wind has advected moisture into the region, keeping
dewpoint temperatures in the mid to upper 70s across northeast
Kansas. With all of this moisture pooling ahead of the front,
PWATs will range from 1.5 to 2 inches indicating efficient
rainfall rates within given thunderstorms.
Temperatures are ranging from the upper 80s to the mid 90s across
the area. Given the excess moisture in the boundary layer, heat
index values have exceeded 105 degrees in spots. A heat advisory
will remain in place for several counties until 7 PM.
For this evening, thunderstorms will begin to form along the frontal
boundary with initial convection likely being isolated.
Development in north-central KS is expected to begin around 6-7pm
and with the line of storms arriving in the Topeka area around
8-9pm. The 0-6 km effective wind shear should remain around 20-30
knots and will begin to push convection into a line as it moves
east. 0-3 km SRH ahead of the boundary should increase to 150-200
as the LLJ increases to around 20-30 knots. With these factors in
mind and the lack of ample deep wind shear, tornado risk is not
high but a few brief tornadoes cannot be ruled out. The main risks
that will come with these storms will be the threat for strong
winds with DCAPE values around 1500 J/kg. Additionally, given
that these storms could produce efficient rainfall rates,
localized flash flooding could be a concern. Brief backbuilding of
storms could also cause concern for flash flooding as the cold
front passes. Widespread rainfall amounts will generally be around
0.25 to 0.75 inches with localized 1-2+ inch amounts.
The cold front will push through the area by Saturday morning
ushering in dryer and cooler air. High temperatures will remain in
the 80s for Saturday but will be followed by a warming trend. A
ridging pattern will set up over much of the south-central US
helping to warm high temperatures back in to the mid to upper 90s
through Wednesday. A few shortwaves could bring chances for
thunderstorms in the early week, but there is not much confidence on
the timing and positioning of these disturbances.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday)
Issued at 546 PM CDT Fri Aug 20 2021
Will use the CAMs consensus for timing TS in the terminals. The
RAP and NAM show a brief period of MVFR CIGS behind the initial
line of convection. So think conditions will improve by daybreak
Saturday. For additional details on convection see the meso
discussion above.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT this evening for KSZ020>023-034>039-
054-055.
&&
$$
MESOSCALE...Wolters
DISCUSSION...Teefey/Griesener
AVIATION...Wolters