Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/19/20
Area Forecast Discussion
National Weather Service Amarillo TX
633 PM CDT Tue Aug 18 2020
.AVIATION...
VFR conditions expected for the 00Z TAF period. Winds will range
between southeasterly and southwesterly between 5-15 kts
throughout the TAF period with sct mid level clouds.
Meccariello
&&
.PREV DISCUSSION... /Issued 201 PM CDT Tue Aug 18 2020/
SHORT TERM...Today through Tomorrow Night...
High pressure remains anchored over portions of NV/UT/AZ/CA with
northwest to northerly flow spreading across the Rocky Mountains
and adjacent plains, becoming more northeasterly flow over the
Panhandles. Several minor perturbations can be identified on the
latest GOES water vapor imagery, with the most notable wave moving
southeast into northeast NE. At the surface, weak southerly winds
were evident across the Panhandles with few clouds as
temperatures were rising into the low 90s. The eastern zones had
dew points around 60, with upper 40s dew points in the west.
Instability was very limited across the area with forecast RAP
soundings indicating too much dry air and unfavorable mid level
temperatures. Thus, dry conditions are expected today.
For tonight, a subtle 600mb to 400mb wave moves down the
northernly flow with 250mb speed max extending from eastern SD to
south central KS. Progged soundings and 700mb theta-E output
indicated an increase in moisture from northwest to southeast just
ahead of the wave. 850mb Theta-E fields stay fairly dry through
tonight, but there may be just enough elevated lift and moisture
to kick off a few showers mainly rooted around 500mb in the
northeastern zones after 06z. While there is some elevated
instability, it is very limited; with values on the order of 200
J/kg. Moreover, while a few thunderstorms can`t be ruled out, most
of the activity will remain showers, and these showers may linger
into Wednesday morning in the eastern zones.
Better 700mb to 400mb moisture will be in place Wednesday
afternoon as northeast flow aloft becomes more northwesterly. This
helps induce stronger lee troughing and better return flow near
the surface, while mid level winds also increase in response to
another subtle mid level wave. With more moisture being in place
and better timing, this wave should support a few thunderstorms
in the area by mid afternoon into the overnight period. Mixing is
also expected to be sufficient so that convective temperatures may
be reached, further aiding isolated storm development in the
afternoon (esp. for southern zones). However, models do suggest
the cap may be fairly strong tomorrow, and this should limit
convective coverage. Any storms that do form will have about 800
to 1200 J/kg MLCAPE to work with, with LCL heights mixing to
around 2000 to 3000m. Therefore, wind would seem like the primary
threat given the high bases expected (DCAPE 1000-1500 J/kg). That
being said, wind fields tomorrow are better than they have been
in some time with plenty of directional shear progged. Effective
bulk shear of around 50 knots will be possible across the central
and eastern zones, with 40 knots across the west in the afternoon
and evening. 0-3km helicity increases to around 300 m^2/s^2 in the
evening supported by a modest low level jet. Thus, if storms can
overcome the cap and become surface based, high based supercells
will be possible. The high LCL values and relatively lacking 0-1km
shear suggest tornadoes are unlikely, however landspouts can`t be
ruled out near any outflow boundaries. Any rotating storm could
produce both large hail and damaging winds.
Storm activity should diminish a few hours after dark, but could
see some lingering activity shift into the southeast zones
depending on timing of upper wave and low level jet.
Ward
LONG TERM (Thursday through Monday)...
The long term will be noted by convection developing off the
higher terrain and potentially moving into the Panhandles by the
evening hours of both Thursday and Friday. Otherwise, confidence
for precipitation into the weekend and next week looks low, albeit
not necessarily zero chances. Temperatures are also seasonable in
the long term ranging from the lower to upper 90s, but a couple
days we will be flirting with triple digits for a few areas.
High pressure will slide south/southeast and become more centered
over the Desert Southwest by Thursday. This may provide us with
more of a northwesterly flow pattern aloft as noted at 700 mb,
resulting in better convection off the mountains impacting the
Panhandles. However, the flow at 500 mb is more northerly which
may lend to less favorable chances across the Panhandles. Chances
for diurnally initiated convection to form off the mountains
Thursday and Friday are looking favorable, but the question is
whether or not the steering flow aloft will allow those
thunderstorms to travel into the Panhandles by the evening.
Forecast soundings suggest a potential 40-50 knot low level jet
(Clayton - 50kts | Dalhart - 40kts) which could further enhance
our chances into the overnight hours (9pm to 2am). For now, it
does look like the western half of the forecast area will have at
least a small chance (20-30%) for thunderstorms in the evening
hours. Severe weather chances do not look all that likely (weak
sheer, low CAPE, limited forcing), but given the inverted-v
soundings we could certainly have some strong wind gusts if we can
tap into some monsoonal moisture aloft (potentially increased by
hurricane Genevieve). The wind field also suggest the storm motion
would be slow around 10-20 mph Fri/Thur evenings.
Beyond Friday, the steering flow aloft does not look favorable for
thunderstorms to impact the Panhandles. Upper level pattern
suggests we could be under northerly/northeasterly flow which
would hinder our thunderstorm chances. That said, we will have to
watch the position of the upper level high out to our west as we
progress into the weekend.
Guerrero
&&
.AMA Watches/Warnings/Advisories...
TX...None.
OK...None.
&&
$$
29/36
Area Forecast Discussion
National Weather Service Bismarck ND
924 PM CDT Tue Aug 18 2020
.UPDATE...
Issued at 924 PM CDT Tue Aug 18 2020
Radar suggests isolated showers over southwest North Dakota.
Despite high cloud ceilings, a couple showers in Hettinger County
now appear strong enough that rain is likely reaching the ground.
This activity appears to be in response to weak mid level forcing
possibly interacting with a N-S oriented surface dryline along and
east of Highway 22. There does not appear to be enough instability
this far west for thunder. Have added a slight chance of showers
to most areas south and west of the Missouri River through 1 AM
CDT. The rest of the forecast remains unchanged.
UPDATE Issued at 821 PM CDT Tue Aug 18 2020
As of this writing, no convection has initiated and it appears
increasingly unlikely that it will with increasing CIN. One
possible exception may be in an area to the south and west of
Devils Lake, where satellite shows an area of altocumulus clouds
expanding in coverage with subtle upstream mid level energy
barely evident on water vapor. We have trimmed back PoPs to just
include a slight chance of thunderstorms from the Devils Lake
Basin southward through the James River Valley and adjacent areas
through the night.
Sky cover was also increased over southwest North Dakota based on
current trends.
UPDATE Issued at 622 PM CDT Tue Aug 18 2020
Convective initiation is starting to look more unlikely. Most CAMs
have trended away from any thunderstorms developing, and recent
RAP soundings suggest CIN will not sufficiently erode. The just-
launched 00Z Bismarck RAOB also shows mixed layer capping. The
18Z NAMNest does still show some potential in the James River
Valley around 8-9 PM, so will leave a slight chance mentioned. If
a storm does develop, the environment remains favorable for a
conditional severe threat.
&&
.SHORT TERM...(This afternoon through Wednesday night)
Issued at 211 PM CDT Tue Aug 18 2020
Temperatures have been coming up a bit quicker than initially
thought this afternoon, and with Medora and Beach already seeing
observed temperatures of 97 thus far, think it is likely that we
will see a handful of sites in the low 100s before all is said and
done. The heat, along with dewpoints in the mid 30s to mid 40s
across the far west, has led to very dry and near critical fire
weather conditions. The good news is that winds should remain
fairly light here through the afternoon, generally 10 to 15 mph
with gusts up to 20 mph.
The other story for this afternoon and evening will be
thunderstorm chances across the central and southern James River
valley. There will be a nice overlap of 35 to 45 knot effective
shear and moderate to strong instability, but the question of
sufficient forcing to break the cap still remains. A
stationary/pseudo warm front is currently just east of the
Highway 83 corridor, drifting east slowly. While this boundary may
serve as the focus for a few updraft attempts this afternoon, it
remains unclear whether we will see enough convergence at the
surface to actually get storms. If updrafts are able to sustain
themselves and break through the cap, a conditional severe weather
threat still remains. It is worth noting that CAMs continue to
show little, if any, development this afternoon or evening.
Later on tonight, a better chance for showers and thunderstorms
looks to be possible across the southern James River valley as
another subtle wave rides down the ridge on the nose of stronger
warm air advection. It isn`t out of the question that one or two
of these storms could become strong to severe.
Wednesday will be another hot day with widespread highs in the mid
to upper 90s. The western third of the state will once again be
very dry with minimum afternoon relative humidity values in the 15
to 20 percent range. Thus, near critical fire weather conditions
will be likely again Wednesday afternoon, but winds will be
light. Another wave will bring slight chances of thunderstorms to
the west and north central Wednesday evening and overnight. With
meager instability and shear forecast, severe weather is not
anticipated with this activity.
.LONG TERM...(Thursday through Tuesday)
Issued at 211 PM CDT Tue Aug 18 2020
Another wave moves through on Thursday with chances of
thunderstorms starting across the southwest in the afternoon and
moving into the central overnight. Instability and shear may be
sufficient for a strong storm or two in the far southwest but
widespread severe is unlikely.
Another chance for some isolated to scattered strong storms looks
possible on Friday across the central and James River valley as
these subtle waves keep trying to flatten the ridge. A slight cool
down and mainly dry weather comes into the picture over the
weekend, but highs will still remain above average for most. The
global models agree that broad troughing will begin to setup
across the western CONUS by the end of the weekend and beginning
of next week, which suggests a possible uptick in thunderstorm
activity next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 622 PM CDT Tue Aug 18 2020
VFR conditions and light winds are expected through the forecast
period. There is a very slight chance of a thunderstorm near KJMS
this evening and tonight.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Hollan
SHORT TERM...ZH
LONG TERM...ZH
AVIATION...Hollan
Area Forecast Discussion
National Weather Service Caribou ME
922 PM EDT Tue Aug 18 2020
.SYNOPSIS...
A cold front crosses the waters this evening. High pressure slowly
builds in Wednesday through Thursday. Low pressure approaches
the region Friday and Saturday.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
915 PM Update: Stronger showers and isolated thunderstorms have
continued a little longer than even what CAMs are showing, so I
xtnded the mention of isold tstms another hr or two into late
eve, thinking that this current activity may be the last of
stronger cnvctn before dissipating ovr the next few hrs.
Otherwise, latest avbl mid eve sfc obs were used to make
adjustments to fcst hrly values of temp/dwpts into the late ngt
with, again, no sig chgs to fcst ovrngt lows needed attm.
Prev Disc: Showers w/isold tstms into early evening as upper
trof interacts w/the slow moving frontal boundary. The strongest
storms will be across the Maine Central Highlands into the
Bangor and Interior Downeast region. Some of the storms could
contain hail and strong wind gusts. Sounding data coming in from
the RAP and NAMNEST showed 0-6km shear around 40 kts w/MU CAPE
climbing to near 1000 joules. Lapse rates are steepening
allowing for good updrafts to keep storms going. Heavy rainfall
also a threat w/PWS around 1.25". Further n, threat is less as
the atmosphere has been worked over earlier rain. However, radar
and satl lightning imagery showing storms in Quebec pushing
east. Not ruling out the potential for some tstms, but potential
is not as high as it is further s. Looking for activity to wind
down later in the evening as the forcing weakens w/the upper
trof pushing e. Expecting some partial clearing later in the
evening into the overnight hrs. SSW winds less than 10 mph to
become W w/speeds about 5 mph or. Will go ahead and add some
patchy fog in for overnight. Cooling down w/overnight temps
dropping into the 50s.
An upper trof in conjunction w/a sfc trof will be the focus for
some showers across northern and western areas on Wednesday.
Lapse rates are forecast to steepen during the day w/some sfc
heating. So, cumulus will pop but question is the extent of the
cloud tops. Given that moisture above limited to below 700mbs,
decided not to mention tstms. Plus CAPE is forecast to be less
than 100 joules. The NAM and GFS support this setup. W winds are
expected to pick up by the afternoon at 10-15 mph. This will
aid in drying things out.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
The exit of low pressure to the north appears to take place quicker,
and thus the core of breezy winds will pass to the north of the
CWA Wednesday night. With stable air overnight, little of these
winds will actually mix down. Exception will be higher terrain
in the Central Highlands where gusts to 35 mph may be possible.
The quicker departure means lighter winds Thursday afternoon as
well. Thus, while RH values will still be lower in the
afternoon, decent widespread rain today and lighter winds means
conditions for elevated fire danger are less likely than
previously forecast. A sustained breeze around 10 mph will still
keep a drying trend through Thursday afternoon.
NW flow becomes W as low levels couple with a zonal jet through
Friday. High pressure to the south will build return flow across
the region as broad low pressure advances from the west. The
system will lack much moisture as southern sources are cut off,
so have kept shower PoPs lower through the day Friday. Cloud
cover across the north will again keep temperatures cooler in
the mid-70s
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The extended continues to feature uncertainty in regards to
location of moisture and forcing.
What is of higher confidence is mentioning the slight chance for
rain showers through the weekend. Moisture will be in vicinity
of the region, and diurnal heating should be able to kick of
some scattered showers during the morning and afternoons,
especially across the north. Canadian has now taken an approach
similar to the ECMWF, creating a weak boundary across central
New England, back across the northern Great Lakes. This will
slowly slide south through the weekend. Northern stream
moisture, while limited, will continue to spread into northern
New England into early week.
Zonal flow remains aloft as surface low pressure intensifies
near the Great Lakes and tracks towards New England towards
Tuesday. This would likely bring warmer temperatures into the
region ahead of it, with cooler air into mid-week.
&&
.AVIATION /22Z TUESDAY THROUGH SUNDAY/...
NEAR TERM: Some IFR/MVFR across the terminals into the evening.
Some tstms are expected mainly KBGR and KBHB airfields. SSW
winds 5-10 mph. Improvement later in the evening into the
overnight w/VFR. The exception to this will be across KFVE for
MVFR cigs. Some MVFR and perhaps IFR overnight into early
morning w/fog.
Wednesday...Basically VFR for all terminals after some MVFR/IFR
for patchy fog. W winds increasing to 10-15 mph.
SHORT TERM:
Wed night: Variable conditions between MVFR and VFR at the
northern terminals from KPQI north in clouds and showers with
VFR expected after midnight. VFR expected from KHUL south to
KBHB. Breezy W winds diminish during the evening.
Thu & Thu night: VFR, gusty WNW winds picking up in the morning
through afternoon. SW near/along the Downeast coast. Winds
slacken in the evening and overnight. Some showers across the
north.
Fri and Fri night: MVFR possible at the northern terminals, but
timing is highly uncertain. Some rain showers possible. VFR
should continue Downeast. Showers increase in coverage
overnight.
Sat and Sun: Variable conditions between MVFR and VFR in
possible showers at the northern terminals during the afternoons.
VFR expected Downeast.
&&
.MARINE...
NEAR TERM: Below SCA criteria right into Wednesday. S wind
becoming SW tonight at 10 kt. Some fog is possible over the
waters. SW winds becoming W on Wednesday and increasing to 10-15
kts. Seas to remain at 2-3 ft.
SHORT TERM: Waves 2 to 3 feet through Friday. Winds remain below
SCA criteria, but approach 25 kt Thursday afternoon from the SW.
Winds slacken through Thurs night. Waves build 3 to 4 ft over
the weekend as low pressure passes north of the waters.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...None.
&&
$$
Near Term...VJN
Short Term...Cornwell
Long Term...Cornwell
Aviation...VJN/Cornwell
Marine...VJN/Cornwell
Area Forecast Discussion
National Weather Service Charleston SC
955 PM EDT Tue Aug 18 2020
.SYNOPSIS...
A weak cold front will stall over or near the region tonight.
This stationary front will remain over the region and gradually
weaken into the weekend. High pressure is then expected to
prevail early next week.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 950 PM: I will update the forecast to remove headlines for
the Coastal Flood Advisory. Residual rain remains across extreme
SE GA and offshore waters. The showers should gradually
dissipate by midnight. I will update temperatures to align with
recent observations.
As of 830 PM: The forecast area has been generally worked over
with convection this afternoon and evening. The remaining
convection appears limited to the marine zones off of SC coast
and just south of the Altamaha River. It appears that the
ongoing convection will continue through the rest of this
evening. Late tonight, HRRR indicates that a few showers and
thunderstorms will linger off the coast, mainly dry over land.
Convection is expected to increase offshore during the pre-dawn
hours as a disturbance approaches from the south.
Previous Discussion:
This evening and tonight: The initial convective cluster
developed across Candler, Jenkins, Bulloch, and Screven
counties. That cluster has thrown out a nice outflow boundary
that is progressing eastward and should continue to kick off new
updrafts as it moves. Further east, the sea breeze is
initiating along the Charleston County coast and is starting to
move to the east within the broader steering flow. SPC
mesoanalysis shows 1,000-1,200 J/kg of DCAPE across much of the
area, so there will be the potential for strong wind gusts. The
main convective cluster was producing 40-50 knot on base
velocity data, indicative of the wind potential in this
environment. We could need a few more Severe Thunderstorm
Warnings before storms weaken later this evening. Also of note,
we will have to monitor convective trends later this evening
around the time of high tide (~8:20 pm) for possible fresh/salt
water flooding issues in Downtown Charleston. Once the diurnal
activity weakens later this evening we should see a lull before
possibly seeing isolated to scattered showers and thunderstorms
late tonight. Models seem to favor the South Carolina coast and
the Charleston Tri-County for this possible late night activity.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Moderate confidence this period. The area will remain between
troughing to the west and ridging to the east which will keep
abundant moisture and periodic upper-level forcing in place.
Combine these factors with mesoscale boundaries from the sea
breeze and convective outflows and the result will be higher
than normal rain chances, mainly each afternoon/evening. Deep
layer shear could increase a bit the next several days but still
be fairly marginal to support much severe weather, however
isolated instances of damaging winds certainly cannot be ruled
out. Temperatures should remain near to slightly above normal.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The mid-level trough over the Lower Mississippi Valley Friday
night will weaken through the weekend. Meanwhile, high pressure
in the Atlantic will gradually shift towards the Southeast U.S.
early next week. At the surface, the stationary front over or
just west of our area will dissipate this weekend, with Atlantic
high pressure approaching the coast. Sea breeze convection will
be possible each afternoon/evening. Though, coverage should be
at or just below normal. Temperatures will be near normal.
&&
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
The forecast area has been generally worked over with
convection this afternoon and evening. Expecting VFR conditions
overnight at KCHS and KSAV. Convection is expected to increase
offshore during the pre-dawn hours as a disturbance approaches
from the south. This activity is expected to spread over KCHS
between 15-18Z, highlighted with a TEMPO.
Extended Aviation Outlook: Occasional flight restrictions are
possible in showers and thunderstorms, especially during the
afternoon and evening hours.
&&
.MARINE...
Tonight: Winds along the land/sea interface will peak in the
10-15 knot range this evening and then should steadily drop off
to 5-10 knots late tonight. Seas will average 2-3 feet. Mariners
should monitor conditions through the evening for thunderstorms
approaching and moving into the local waters, capable of
producing strong wind gusts.
Wednesday through Sunday: Moderate to high confidence this
period. A stationary front will remain inland the next few days,
gradually weakening into the weekend. High pressure is then
expected to prevail early next week. Expect backing winds to the
south/southeast each day near the coast along with some higher
gusts due to the sea breeze. At night, winds should veer more
southwesterly as the land breeze and nocturnal jet form.
Conditions overall should remain below Small Craft Advisory
levels but mariners can expect gusty winds in/near
thunderstorms, and the potential for isolated waterspouts to
form along the land breeze each morning.
&&
.TIDES/COASTAL FLOODING...
For the evening high tide, current tidal departures are running
around 0.8 ft and we should be on track for the Charleston
Harbor to peak around 7.3 ft MLLW. A Coastal Flood Advisory has
been issued for high tide around 8:20 pm.
Astronomical contributions from the new moon and perigee will
result in elevated tides (the Perigean Spring Tides) through the
week. At least minor coastal flooding and associated Coastal
Flood Advisories will be possible around the times of the
evening high tides through at least Thursday, and especially
along the South Carolina coast. If heavy rain coincides with
these elevated evening tides, significant flooding could develop
in some areas, especially in downtown Charleston.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
NEAR TERM...NED
SHORT TERM...RJB
LONG TERM...MS
AVIATION...NED
MARINE...BSH/RJB
TIDES/COASTAL FLOODING...
Area Forecast Discussion
National Weather Service Cheyenne WY
545 PM MDT Tue Aug 18 2020
.SHORT TERM...(This evening through Thursday night)
Issued at 128 PM MDT Tue Aug 18 2020
Tonight...The HRRR model suggests no more than isolated evening
thunderstorms on tap, which looks reasonable considering CAPE and
warm temperatures aloft. Could see a few strong thunderstorms
across the Nebraska Panhandle where CAPE will be locally higher.
Wednesday/Wednesday evening ...With slightly cooler temperatures
aloft, and the addition of increased low and mid level moisture, we
expect to see an areal increase of afternoon and evening
thunderstorms, mainly along a low level convergence axis from
Douglas to Cheyenne in the afternoon, then across the Nebraska
Panhandle in the evening where storms will transition to.
Thursday/Thursday night...Heights aloft continue to decrease, and
with adequate low and mid level moisture, we expect isolated to
scattered late day shower and thunderstorm coverage. Slightly cooler
compared to Wednesday.
.LONG TERM...(Friday through Tuesday)
Issued at 128 PM MDT Tue Aug 18 2020
Ridging aloft prevails Friday through Sunday, and with limited
low and mid level moisture, mostly dry conditions should prevail.
Zonal flow aloft prevails for Monday and Tuesday, with enough
moisture for at least isolated late day thunderstorms on Tuesday.
Temperatures will continue above climatological normals.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 527 PM MDT Tue Aug 18 2020
VFR flight conditions expected at all terminals through 6Z. A very
low chance of VCSH for the western Nebraska Panhandle terminals
this evening, so they were omitted in the TAFs. Wind gusts should
dissipate to 10 knots or less near 2Z. Model guidance from the
HRRR shows that smoke from the CO wildfires should stay to the
south of the state line overnight into tomorrow morning. High
level CIGs may hover overnight due to the transition into
northwest flow at the higher levels of the atmosphere by 6Z
tonight.
&&
.FIRE WEATHER...
Issued at 128 PM MDT Tue Aug 18 2020
An unusually hot and dry weather pattern continues with
widespread highs in the 90s and minimum RHs in the lower teens and
upper single digits. This is creating a favorable situation for
new fire starts given the fuels status. Despite this, fire weather
concerns should remain fairly low with winds below critical
thresholds. Increasing chances for thunderstorm activity through
Thursday. Any thunderstorms may produce gusty and erratic surface
winds, as well as frequent lightning. Dry thunderstorms do not
appear particularly likely with sufficient low-level moisture, but
storms will still be on the high-based side.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning from noon to 8 PM MDT Wednesday for WYZ301>303-
305>310.
NE...None.
&&
$$
SHORT TERM...RUBIN
LONG TERM...RUBIN
AVIATION...BW
FIRE WEATHER...RUBIN
Area Forecast Discussion
National Weather Service Grand Forks ND
1032 PM CDT Tue Aug 18 2020
.UPDATE...
Issued at 1031 PM CDT Tue Aug 18 2020
Not much going on currently, with mostly clear skies. Can`t
completely rule out some isolated/widely scattered storms
developing later tonight as a weak shortwave comes down out of
southeast Saskatchewan, but not overly impressed as given lack of
current activity in that area. Will continue to keep some low POPs
after midnight.
UPDATE Issued at 719 PM CDT Tue Aug 18 2020
Showers that tried to get going dissipated under a pretty strong
cap, and CAMs have backed off on convection this evening. Still
could see some storms later tonight as the shortwave moves down,
with some elevated CAPE around 1000-1500 J/kg later tonight can`t
rule out some stronger cells pulsing up. Removed POPs for this
evening but will keep isolated-scattered storms after midnight.
&&
.SHORT TERM...(This afternoon through Wednesday night)
Issued at 307 PM CDT Tue Aug 18 2020
Monitoring severe potential for this afternoon and evening, with a
few marginal cells possible.
Weak southerly surface gradient is in place with some return flow
resulting in warmer temps and slightly increased Td values in the
60s. Objective RAP analysis showing ML CAPE has increase to around
1500 J/KG, however CIN remains high and this capping is keeping
activity elevated in nature (and as a result much weaker) where a
few showers (occasional lighting) in southeast ND at the time of
this discussion.
This afternoon-tonight: Next embedded impulse is just now moving
into southern Manitoba and should progress down the RRV this
evening/overnight. Additional afternoon mixing could help weaken
capping, so I can`t rule out storm initiation before the main
period of forcing arrives, but latest runs of the HRRR are very
promising. Overall chances for showers/storms increase as the
evening goes on (likley remaining scattered) with the strongest
QPF consensus from CAMs after 03Z...of course this would be after
instability decreases. There is enough variance between CAMs in
track/coverage that I can`t rule out activity just about anywhere
in our CWA, but confidence overall isn`t high. There is a window
where ML CAPE 1500-2500 J/KG may coincide with 25-30kt effective
shear to support marginal severe storms through early evening. In
addition, DCAPE is shown to remain 1000-1500 J/KG this evening
raising the possibility for microburst potential. Pulse type
severe convection appears favored, with hail to 1 inch and 60 mph
winds the main concern through sunset.
Wednesday-Wednesday night: Combination of rising heights/increasing
low level southerly flow will result in even warmer temps higher
humidity Wed, with highs in the 80s to near 90 (warmest in ND). If
they develop tonight, lingering elevated showers/storms should
exit our region Wednesday morning to the south/southeast with
models favoring a period of subsidence dry conditions during the
day. WAA/low level moisture increases, so we actually see higher
CAPE values reflected in guidance across our south by the
afternoon. Capping and a lack of forcing will limit thunderstorm
potential where the parameters would be more favorable to
strong/severe storms. The next impulse that could support storm
initiation doesn`t arrive until later Wednesday evening and NBM
has limited PoPs (slight chance) along the international border.
Parameters do not appear favorable for severe in our north.
.LONG TERM...(Thursday through Tuesday)
Issued at 300 PM CDT Tue Aug 18 2020
An upper level ridge will remain in place over the High Plains
through the first part of the extended period...with minor
perturbations tracking through the flow helping trigger shower/isold
storm activity.
The upper ridge will be to gradually weaken and become more zonal
into the weekend. Expect a weak front to drop across the area for
Sunday night and Monday with another chance for precipitation. Will
see temps cool down for the end of the period...with highs around 80
and lows in the upper 50s which is near seasonal averages.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 719 PM CDT Tue Aug 18 2020
VFR conditions at all TAF sites and that will continue through the
period. Some scattered to isolated convection, best chances around
KFAR after midnight so only have a mention there. Winds from the
south will shift to a more southwesterly direction tomorrow
morning, but will be mostly under 12 kts.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...JR
SHORT TERM...DJR
LONG TERM...Hopkins
AVIATION...JR
Area Forecast Discussion
National Weather Service Green Bay WI
1038 PM CDT Tue Aug 18 2020
Updated aviation portion for 06Z TAF issuance
.SHORT TERM...Tonight and Wednesday
Issued at 356 PM CDT Tue Aug 18 2020
The latest RAP analysis and satellite/radar imagery show high
pressure stretching from northwest Ontario to the central Great
Plains early this afternoon. Daytime convective clouds popped by
late in the morning across the region, but the vertical extent is
not nearly as high as the past few days. Looking to the northwest,
mid-level warm advection is occurring over northwest Ontario, with
a few showers reported northwest of Lake Superior. As this warm
advection zone spreads southeast, forecast concerns mainly revolve
around shower chances over northern WI.
Tonight...High pressure will remain centered across the region.
The warm advection and associated cloud cover will slide southeast
across the Upper Peninsula and northern WI through the night. But
models portray mid-level lapse rates and elevated instability as
relatively weak, and keep most precip chances north of the U.P.
border. Will carry a very small chance of a shower right near the
border after midnight. Temps should be warmer than last night due
to more cloud cover. Lows ranging from the upper 40s in the cold
spots to the middle 50s.
Wednesday...The warm advection zone will proceed southeast across
northeast Wisconsin. Mid-level instability and moisture
convergence appears to remain north of the U.P. border once again,
so will leave a slight chance across the far north. Should see
more in the way of cloud cover, but warming low level temps will
offset. Highs ranging from the upper 70s to lower 80s.
.LONG TERM...Wednesday Night Through Tuesday
Issued at 356 PM CDT Tue Aug 18 2020
The main highlights for this forecast period are the various chances
for showers and storms across far northern Wisconsin through Friday
and the potential for a more significant system to move over the
region late Friday night through late Saturday night.
Wednesday night through Friday...The upper-level northwest flow will
remain dominant over the western Great Lakes region through this
period. At the surface, a nearby high pressure system will keep
conditions mostly sunny and dry across much of central and east-
central Wisconsin. Weak WAA across the northern Wisconsin/Upper
Michigan border throughout this time period will allow clouds to
develop. Isolated showers and non-severe storms may also develop
over this area at times as well. The upper-level northwest flow will
begin to flatten into Friday afternoon ahead of an approaching
shortwave.
Friday night through Saturday night...Although this time period
looks to be the best chance to see widespread showers and storms,
there are many uncertainties. Model guidance is in good agreement
with the broad synoptic characteristics with a shortwave moving
across the region during this time period. However, the ECMWF and
Canadian continue to show this as a relatively weak system while the
GFS has a much stronger system moving across the region. As
mentioned in previous forecasts, the GFS continues to not have much
support from its ensemble members, so will avoid this solution.
Since the models have slowed the overall system`s progression to
move over the region sometime between early Saturday morning and
Saturday evening, the system may be able to tap into enough
instability during peak heating to produce some strong to severe
storms. Deep layer shear appears to be limited during the system`s
passage which would hinder storm organization, however, PWATs are
approaching 1.75 inches. Any showers or storms that develop during
this time period could bring heavy rain. Will continue to closely
monitor as changes are expected to occur within the next 3 to 4 days
with this system.
Rest of the extended...Once the shortwave system exits the region
Saturday night, the forecast area will see the return of an upper-
level northwest flow and a surface high pressure system for Sunday
into early next week. This will bring slightly cooler air back to
the region causing either slightly above normal or near normal
temperatures.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 1037 PM CDT Tue Aug 18 2020
Aviation weather issues during the next 24-36 hours are expected
to be relatively limited in duration and coverage. Middle clouds
will drift into the area from the north at times, and diurnal
clouds with VFR bases are expected during the mid-day and
afternoon hours. It still looks like patchy fog will probably
develop again tonight (like the past several nights) in north-
central Wisconsin. Will carry a tempo group with IFR vsbys in the
KRHI TAF to account for it.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM.....MPC
LONG TERM......Hykin
AVIATION.......Skowronski
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1058 PM CDT Tue Aug 18 2020
.UPDATE...
Issued at 1048 PM CDT Tue Aug 18 2020
Updated to include 06z aviation discussion below.
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 239 PM CDT Tue Aug 18 2020
High pressure will keep the weather mainly dry for the next couple
of days. The lone exception is a weak disturbance that could bring
some showers and possibly a thunderstorms across the region north
of I-94 late tonight into Wednesday morning. Highs on Wednesday
will be a few degrees warmer than today.
Early afternoon satellite imagery and RAP surface analysis showed
high pressure over the Upper Mississippi River Valley. A few
cumulus developed on the eastern side of this surface high,
while areas to the west were mostly clear aside from a few high
clouds. The only precipitation to speak of was some weakening
showers in eastern North Dakota.
A strong upper level ridge was set up across the western CONUS,
and weak shortwave troughs will ride this ridge across the Upper
Midwest. One of these features was currently located across
southern Manitoba, and HiRes models are in good agreement with
developing scattered precipitation as the PV anomaly slides
southeast later tonight into Wednesday. Mid level lapse rate on
the order of 7 to 7.5 C/km will allow around 1000 J/kg of MUCAPE
to develop over northern Minnesota but just a fraction of that
will develop across the northern part of the Twin Cities forecast
area in central Minnesota and west central Wisconsin. Forecast
soundings show cloud bases around 10kft, so expect scattered high-
based rain showers, and possibly some thunderstorms to the north
late tonight into Wednesday morning.
.LONG TERM...(Thursday through Tuesday)
Issued at 239 PM CDT Tue Aug 18 2020
This period continues to be dominated by the almost stationary
upper ridge over the western CONUS. Early next week this upper
ridge will begin to dissipate and allow for a pattern change
across the CONUS.
Expecting warmer weather Thursday and Friday ahead of a cold front
moving through the Upper Midwest. Ahead of this cold front
temperatures will be in the 80s with some temperatures near 90
possible in western Minnesota. Behind this cold front temperatures
should fall back to near normal this weekend into next week. This
cold front will also provide our best precipitation chances,
mainly on Friday and Saturday. Ahead of the front daytime heating
could lead to an unstable environment with surface based CAPE
values around 3000 J/kg. This would support thunderstorms Friday
and Saturday. The shear in this environment is less certain so
there remains uncertainty in how strong storms could be. There is
another possible chance for precipitation early next week as
another front passes through the Upper Midwest.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1048 PM CDT Tue Aug 18 2020
VFR with high pressure moving east of the region over the next 24
hours. Mainly clear skies but there is a small chance of a few
SHRA/TSRA north of I-94 from the pre-dawn hours into late morning.
Potentially only the WI sites may experience any issues. Chances
are too low for inclusion at this point but it does bear some
watching as the 12z TAF set approaches. Otherwise, light
southerly winds overnight become more SW during the day Wednesday
with speeds near 10kt.
KMSP...No additional concerns.
/OUTLOOK FOR KMSP/
Thu...VFR. Wind SSW at 10-15 kts.
Fri...VFR with -TSRA possible late. Wind SW at 10 kts
Sat...VFR with TSRA possible. Wind S at 10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
UPDATE...JPC
SHORT TERM...JRB
LONG TERM...NDC
AVIATION...JPC
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
923 PM EDT Tue Aug 18 2020
.UPDATE...
EVENING UPDATE.
&&
.DISCUSSION...
PoPs will need to be rasied in northern sections with the evening
update as showers and thunderstorms moving out of KY and Middle TN
have held together. Radar shows a weakening trend to the showers,
and this should continue as heating is lost and the upper jet
streak pulls farther away. Some temp/dewpoint adjustment will also
be made to better align with current obs, but lows in the 60s are
on track.
DGS
&&
.AVIATION...
00Z TAF DISCUSSION.
Showers and thunderstorms across KY and Middle TN will gradually
move into East TN, but they will be weakening after sunset as
heating is lost and they encounter drier air. So for the TAFs,
only TRI is expected to have a threat of TS and MVFR conditions.
Tomorrow afternoon, showers and thunderstorms are expected to
develop and be more numerous around the area as an upper level
trough approaches, so a PROB30 will be mentioned at all sites,
along with VCTS.
DGS
&&
.PREV DISCUSSION...
/ISSUED 331 PM EDT Tue Aug 18 2020/
SHORT TERM...(Tonight and Wednesday)
Key Messages:
1. Widely scattered showers/storms, mainly north of I-40, developing
late this afternoon through tonight, but no heavy rain expected.
2. Showers/storms increasing through the day Wednesday with cooler
temps, but most areas will see light to moderate rain totals.
Discussion:
Late afternoon/evening...
Latest satellite and RAP analysis at 1830Z shows a vigorous H5
shortwave rotating through the MS Valley downstream of a 600 DM heat
ridge over the western CONUS. The axis of the H5 shortwave was
oriented from roughly S IL through W TN with a weak surface low over
central KY. One cold front extended S from the low through W TN and
MS while a second cold front was draped across S GA and the
Carolinas. As the H5 shortwave and associated surface low and cold
front continue slowly eastward this evening, scattered convection
will materialize from the N Plateau through NE TN and SW VA in
response to diffluence under the right entrance region of a 40-60 kt
H30 jet, convergence ahead of the approaching low-level boundary,
and some weak instability from daytime heating. However, coverage of
convection will be widely scattered due to the continued presence of
significant dry air through the column and only about 200 J/Kg of
MLCAPE and less than 1000 J/Kg of surface CAPE. This drier air is
keeping PWAT values slightly below the climatological average at
1.15 to 1.25 inches, so any convection will only contain moderate
rainfall rates.
Tonight and Wednesday...
The aforementioned H5 shortwave will continue to press through the
TN valley overnight with the surface cold front slowly moving into
the region. This front is progged to be oriented up the Valley by
12Z. In the wake of this initial shortwave, a deep, positively
tilted mid/upper longwave trough will be reinforced over the MS
Valley placing a belt of strong SW flow aloft over the S
Appalachians and Carolinas aligned parallel to the low-level front.
This will cause the front to stall in the vicinity of the S
Appalachians and western Carolinas Wed. In terms of precip, pulled
back PoPs tonight to chance/slight chance, with greatest potential
over far northern areas. The reason being that the shortwave is
timed with the diurnal minimum, mid level moisture will still be
slow to increase, and the best jet dynamics look to progress farther
away overnight leaving only weak upper diffluence over our region.
Better chances for showers/storms will arrive Wed afternoon through
the evening as a secondary shortwave dives through the mid MS Valley
and approaches the region. As this second shortwave further deepens
the longwave trough, another 40-60 kt southwesterly H30 jet streak
will develop over the central Appalachians placing the region in the
favored right entrance, and this upper jet will also strengthen the
low-level southerly flow leading to increasing moisture, isentropic
ascent, and convergence along the stalled frontal boundary. This
will allow for widespread showers/storms increasing from late
morning through the afternoon as daytime instability builds. MLCAPE
of 1500-2000 J/Kg and the deeper lifting will allow for locally
heavy downpours, but PWATs will only increase to 1.3 to 1.6 inches
which will keep the heaviest rain spotty. Have widespread likely
PoPs Wed afternoon with some categorical PoPs in SE TN and along the
mountains closer to the boundary. Went slightly below the NBM for
highs due to mostly cloudy skies and greater precip coverage.
Garuckas
LONG TERM...(Wednesday Night through Tuesday)
A wet extended period will take place for several days but will
start to change Sunday. Mid and upper level trough over the eastern
states Wednesday night through Saturday at least. A weak front
across the forecast area Wednesday night will help to focus
scattered to numerous showers and storms well into the evening. A
weak closed upper low is also forecast to form across the lower Ohio
and western Tennessee Valleys from about Wednesday night and
continue through Saturday morning. Weak shortwaves moving in from
the west and northwest will be enhanced by the upper low and any
surface boundary still lingering over the region. Periods of showers
and some thunderstorms are expected each day and into at least the
evenings during this time. Some heavier rainfall amounts will be
possible Friday and Friday night especially along the eastern
mountains and across southwest North Carolina which could produce
some localized flooding. Starting Sunday the trough begins to shift
to the northeast and ridging strengthens over the southeast states.
Showers and thunderstorms will be less widespread and be more
numerous in the higher elevations. Temperatures will be below normal
from Thursday through Saturday in the lower to mid 80s and then warm
into the mid 80s to lower 90s the last 3 days.
TD
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 69 89 67 85 68 / 20 70 20 70 60
Knoxville McGhee Tyson Airport, TN 67 86 66 84 67 / 20 60 20 60 40
Oak Ridge, TN 66 86 65 84 68 / 30 60 20 60 30
Tri Cities Airport, TN 63 83 62 81 64 / 40 60 20 60 40
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
Area Forecast Discussion
National Weather Service Phoenix AZ
900 PM MST Tue Aug 18 2020
.SYNOPSIS...
Strong high pressure will continue to dominate the weather pattern
and maintain very hot conditions. High temperatures across the lower
deserts will be near or above 110 through the next 7 days. Isolated
thunderstorms with strong gusty winds and areas of blowing dust will
be possible this afternoon and evening across south-central, west
and southwest Arizona. The more favorable monsoon pattern will
continue as moisture increases over the weekend.
&&
.DISCUSSION...
At 8 pm this evening, an exceedingly strong upper level ridge
remained parked across the western states; latest 500mb plot
depicted 599dm heights over northern Arizona with values around 596-
597dm over the central deserts. The high temperature in Phoenix
reached to 115 again today and that makes 5 of the last 6 days with
a high of 115 or greater! Moderately strong northeast steering flow
of 15-20kt supported convection moving into the central deserts from
the eastern Rim, however surface dewpoints in the 40s over the
deserts does not provide the best support for storms holding
together after they move off the high terrain and into the low
elevations. For most of the afternoon and early evening, storms have
been minimal over the central deserts with little in terms of
outflow winds. However, it appears that at least one last wave will
be moving in from the east/northeast during the mid to late evening,
leading to some shower activity with possibly an embedded storm.
CAPE not overly high from the evening sounding, although latest SPC
mesoanalysis graphic showed a pocket of MLCAPE around 1000j/kg to
the northeast of Phoenix. We can expect some gusty easterly outflow
winds starting to move through the greater Phoenix area after 930 pm
along with some convective activity. After midnight convection
should dissipate leaving behind partly cloudy skies. Forecasts have
been tweaked and look to be in decent shape.
.PREVIOUS DISCUSSION...
Strong high pressure remains situated just to the northwest, putting
our region under east-northeast flow. With little change in the
environment since yesterday, we will once again see a chance for
storms over the AZ high terrain to move toward the lower deserts.
The best MLCAPE early this afternoon is over western AZ and southern
CA, where moisture is higher. Already seeing strong storms in
southern CA, including in Joshua Tree National Park. 12Z HREF does
suggest slightly better chances for storms to progress into portions
of southwest AZ and southeast CA later this evening on strong
outflows from west-central AZ. MLCAPE is nonexistent in southeast
AZ, including the Phoenix area early this afternoon, which means
convective initiation is heavily dependent on surface heating
through the rest of the afternoon. SBCAPE is still minimal at the
moment over the same areas. HREF keeps SBCAPE on the low end, so it
will likely be tough to get storms too far south off the eastern Rim
(i.e. south of Gila county). HRRR is still the most aggressive CAM,
but has done fairly well the past couple of days, and does have
isolated strong storms push into the Globe area east of Phoenix. It
is tough to say whether storms will be able to maintain strength
into the Phoenix area late this afternoon and evening, but should at
least see outflow winds push in from the east to northeast and we
shall see if the outflows will be strong enough to develop new
storms. DCAPE is still high around 1500 J/kg across the lower
deserts, which does support strong outflows that may once again kick
up a lot of dust. One additional note, nearly all GEFS members have
been consistent the past couple of days showing measurable precip
(0.1") in downtown Phoenix this evening. So there`s some hope if you
want to believe the GEFS. The EPS remains dry, but has been
consistently too dry. Any storm this that develops this afternoon
and evening will have the primary threat for strong to severe
downburst winds, which again may kick up a lot of dust, but
localized flash flooding and lightning are also concerns.
With the strong high pressure still dominating the weather pattern,
extreme temperatures will continue. An Excessive Heat Warning
remains in effect through this Thursday for south-central AZ to
southeast CA. Temperatures should trend slightly cooler the next few
days and into the weekend as the high pressure weakens and drifts
southeast back toward central AZ. Despite the location of the high
being closer, high temperatures are favored to finally stay below
110 for a few days. Unfortunately, this may not last as GEFS and EPS
mean show the high restrengthening and shifting back northwest by
early next week.
Hurricane Genevieve is currently off the central Mexican west coast
and is expected to track northwest, staying west of Baja California.
NAEFS and EPS mean do show a slight increase in moisture pushing
into the southwest by this weekend, with PWATs climbing up to 1.5-
1.8 across the area. This should continue to support daily
thunderstorms. Storm chances in for the lower deserts do drop off
for the end of the week and early weekend with the high placement
and weaker/less favorable steering flow.
However, with the high eventually shifting back northwest and the
moisture in place, we should see better storm chance return by early
next week.
&&
.AVIATION...Updated at 0000Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Conditions remain somewhat favorable for another evening of isolated
convection into the Phoenix area, given decent easterly steering
flow and a weak disturbance rotating around the high and into the
central deserts. Dewpoints however remain rather low and in the 40s,
not what we would like to see for sustaining high terrain storms
into the low desert. Better chance for gusty outflow winds; first
shot of outflow from the north/northeast after 01z and after about
03z, maybe another burst from the east to southeast. Have played out
this narrative in the TAFs but backed off a bit on the blowing dust,
going with a TEMPO group for vis around 4-5SM at the terminals. Kept
gusts generally 25kt or less. Given that most of the hi-res models
that we looked at are not overly bullish on strong outflows into the
Phoenix metro this evening, confidence is not especially high. This
will be a tricky evening. Do not expect overly low cloud bases with
FEW-SCT around 9-10k and BKN-OVC decks aoa 15k feet this evening;
clouds to thin after midnight becoming mostly FEW-SCT mid/high
debris decks. Winds should favor the east at the TAF sites after
midnight and thru late morning before turning to light southwest
after 19z Wednesday.
Southeast California/Southwest Arizona including KIPL and KBLH:
Chances for evening convection a bit better than normal today but
mainly across portions of La Paz and eastern Riverside county. Have
no mention of convection at KIPL, just winds favoring the southeast.
Do feel that an isolated shower or storm could affect KBLH after 03z
so kept the VCTS going at the TAF site until 06z. Winds could gust
up to about 30kt from east or northeast should storms develop and
threaten the terminal. Clouds should not be overly low tonight, just
FEW-SCT 9-10k feet and SCT-BKN aoa 15k feet this evening with clouds
thinning after midnight becoming mostly FEW-SCT mid/high level
debris cloud decks. Winds should generally favor the south to
southwest next 24 hours at KBLH when outflow winds are not present.
&&
.FIRE WEATHER...
Friday through Tuesday:
High pressure will persist across the Desert Southwest this week
but will weaken slightly, resulting in a slight decrease in
temperatures from excessive heat thresholds seen earlier in the
week. Moisture will also begin to increase Friday into the weekend
associated with remnants of Hurricane Genevieve in the eastern
Pacific. The increased moisture may become a bit more favorable
for thunderstorm activity, even across the lower deserts, although
primary storm chances will stay across high terrain areas to the
east of Phoenix each day. Min RH will drop into the teens each day
with overnight recoveries generally in the 35-50% range, but
higher from SW AZ to SE CA. Winds will generally remain light
aside from some typical afternoon breezes. However, any storms
that develop have the potential to produce gusty, erratic winds.
&&
.CLIMATE...
Record high temperatures:
Date Phoenix Yuma El Centro
---- ------- ---- ---------
8/18 112 in 2011 116 in 1960 115 in 2015
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ530>556-
559>562.
Heat Advisory until 8 PM MST Thursday for AZZ557-558-563.
CA...Excessive Heat Warning until 8 PM PDT Thursday for CAZ560>570.
&&
$$
DISCUSSION...CB
PREVIOUS DISCUSSION...Benedict
AVIATION...CB
FIRE WEATHER...Rogers
CLIMATE...MO
Area Forecast Discussion
National Weather Service Blacksburg VA
837 PM EDT Tue Aug 18 2020
.SYNOPSIS...
Low pressure will slowly approach the area from the
lower Ohio River Valley today. The system looks to stall across the
area for the remainder of the week as waves of energy roll on
through. This will bring back the need for the umbrella with
increasing shower and storm chances areawide. Storm chances start to
lower a bit heading into the weekend ahead.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
As of 820 PM EDT Tuesday...
The most significant changes made at this time were to the pops
and temps. Ramped up pops further east and south as scattered
activity continues along the entire length of the Blue Ridge
with the main area of showers/thunderstorms creeping into the
western zones from KY and WV. HIRES simulated radar from HRRR
and NAMNest show a new area of showers/thunderstorms developing
overnight just to our west and then moving across CWA during the
late night/early morning hours. Thus, pops were adjusted to show
this. Temperatures running a bit cooler than expected due to
cloud cover this afternoon and spotty showers. However,
dewpoints were running a bit higher than expected, so cooling
overnight may not be quite as pronounced as earlier thought.
As of 155 PM EDT Tuesday...
A noticeable difference this afternoon as the humidity slowly starts
to build thanks to southwesterly flow. Temperatures are also a nudge
warmer with upper 70s and low 80s west of the I-81 corridor and mid
to to upper 80s off to the east. Radar remains clear as 1730z with
some development off to the west of Charleston, West Virginia and
down to the south of WIlkesboro, North Carolina. This development is
associated with a digging upper level trough and approaching area of
low pressure from the Ohio River Valley. SBCAPE values currently sit
between 1000-1500 j/kg across our region with higher instability
values of 2000-2500 j/kg off to the west across southern Ohio and
Indiana. Currently no mention of severe weather from the Storm
Prediction Center but isolated to scattered convection looks to be
expected in areas north and west of the US-460 and I-64 stretch
heading into the early evening hours. PWATS still remain low at 1.0
to 1.2 inches across the region but some recovery is expected
overnight when the overall weather pattern for the rest of the week
is expected to change.
PWATS by Wednesday morning should recover back to 1.4 to 1.6 inches
as humidity values rise a bit more. This leaves a chance of showers
especially in areas over the mountains west of the Blue ridge along
with some areas of patchy fog in the river valleys. Fog will burn
off quickly after 14z and with some holes in the clouds, convection
should start to form after 18z Wednesday afternoon. With the low
pressure system pushing through and the trough in place coverage
looks to be widespread. Locally heavy rainfall can be expected with
the potential for localized flooding. Storm coverage starts to drop
off by Wednesday evening with some leftover chance pops and patchy
fog heading into Thursday morning.
Temperatures during the period will remain at or slightly below
average.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 135 PM EDT Tuesday...
An upper trough west of the Appalachians Thursday will deepen
and slowly move east into Friday night. This will increase
diurnal convection chances in Friday as the increased southerly
flow increases moisture into the region. A surface boundary will
remain across the Southeast generally from the coast of the
Carolinas into the Gulf Coast states. An area of high pressure
over the Mid-Atlantic region Thursday morning will slide east
into the Atlantic ocean by Friday. With recent heavy rains,
there is the potential for flooding depending on the locations
and intensities of the thunderstorms.
Temperatures during the short term period will be cooler than
normal, with high readings generally from the mid 60s in the
mountains to the lower 80s in the piedmont. Overnight low
temperatures will vary from the mid 50s in the mountains to the
upper 60s in the piedmont.
Forecast confidence is high during the short term period.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 135 PM EDT Tuesday...
The pattern through Sunday will be dominated by a strong ridge over
the Four Corners region of the US, while continued troughing remains
over the eastern half of the US with a Bermuda high settled over the
Atlantic. Embedded pieces of energy will round the base of the
longwave trough. The aforementioned, coupled with ample moisture
settled in place, this will bring daily chances of showers and
thunderstorms through Sunday.
By the first of next week, models begin to break down the strong
ridge over the western states and trough over the east, giving way
to broad ridging over much of the CONUS. Without much forcing,
showers and storms will become more isolated and
diurnal/orographically driven.
Temperatures will remain near normal through the weekend, to
slightly above normal through the beginning of next week.
&&
.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
As of 830 PM EDT Tuesday...
Mostly VFR conditions still in place, but wetter, more humid,
more unsettled weather expected for the remainder of the week. A
weak cold front will sag into the region from the northwest
tonight and stall across the area Wednesday, similar to the past
several events. Isolated showers have popped up along the entire
length of the Blue Ridge from time-to-time this
afternoon/evening, and that continues as of now with about 10%
coverage at the moment. Meanwhile, a larger area of diminishing
showers/thunderstorms was approaching the area from the west.
This activity is expected to reach the western counties within
the next couple of hours and gradually decrease as it spreads
further east. Showers and thunderstorms are expected to
redevelop just to our west across far southwest VA/eastern
TN/eastern KY later tonight and then spread further into the CWA
by daybreak. Thus, have included or introduced VCSH and -SHRA
accordingly as this precipitation is expected to enter the
western areas around 06Z-08Z then diminish as it moves east.
More robust and widespread showers/thunderstorms are expected to
develop during the afternoon along and east-south of the Blue
Ridge. Periods of MVFR conditions will accompany the
showers/thunderstorms.
Thickening clouds and precipitation overnight will limit the
development of dense fog. Have limited time and duration of such
and confined mainly to BCB and LWB. Ceilings will be mostly VFR
this evening, then drop into the MVFR range early Wednesday,
remaining mostly MVFR to VFR during the day Wednesday.
Winds are expected to be chaotic and light, mostly southwest
this evening becoming northeast early Wednesday, then veer back
to a southerly direction by Wednesday evening.
/Confidence in Forecast Parameters/
Ceilings - Moderate to High,
Visibility - Moderate to High,
Winds - Low,
Thunderstorm Potential - Moderate.
Extended Aviation Discussion...
A slow moving and deepening area of low pressure aloft will evolve
to our west resulting in abundant tropical moisture being drawn
northward into the region and a return of MVFR conditions due
to widespread showers and thunderstorms for the remainder of the
week. Some improvement to aviation is expected as we head into
the weekend.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...ET
NEAR TERM...ET/KK/RAB
SHORT TERM...KK
LONG TERM...BMG
AVIATION...ET/KK/RAB
Area Forecast Discussion
National Weather Service Las Vegas NV
200 PM PDT Tue Aug 18 2020
.SYNOPSIS...Excessive heat will last through much of the week
with continued record temperatures. Isolated thunderstorms will
continue into the evening across northwest Arizona and parts of the
Mojave Desert and drift gradually westward while accompanied by
strong wind gusts. A very slight lowering of temperatures is
expected late in the weekend into early next week as high pressure
shifts slightly eastward.
&&
.DISCUSSION...tonight through Tuesday.
Tonight...Convection has started firing over the higher terrain of
the southern Great Basin and Mojave Desert. Look for storms to move
off the higher terrain and into the nearby valleys, i.e Owens Valley
and Morongo Basin/Barstow. HRRR has been consistent in showing
convection propagating west-southwest across southern Mohave County
and into the lower Colorado River late this afternoon, between 5 and
7 pm. Primary concern will be gusty winds as forecast soundings
depict Invert-V profiles with plenty of DCAPE. Localized heavy
rain/hail possible under stronger cores as well but storm motion
should inhibit the threat of flooding. HRRR, as well as other HREF
members indicate convection will dissipate by late evening. Outside
of smoke/haze from nearby fires skies will be mostly clear to partly
cloudy overnight.
Wednesday-Tuesday...The anomalously massive ridge is forecast to
slip southeast and weaken by just a tad by the weekend. Instead of
of H5 heights hovering between 597-600 dm they will dip to between
591-594 dm. Bottom line, this will keep temperatures running well
above normal going into the weekend and the start of next week. The
Las Vegas high temperature is not forecast to be below 110 degrees
until Sunday. Numerous daily record highs/high minimum temperatures
will continue to be broken/tied along with record consecutive days
of highs above a specific temperature. Will keep our heat product
going through Thursday with option to extend in the the coming
shifts.
Isolated thunderstorms remain possible for the region Wednesday and
Thursday, specifically favoring the higher terrain. As the high
slowly shifts off to our southeast models indicate drier and more
stable air wrapping into the western periphery of the high leading
to the removal of thunderstorm potential over the southern Sierra
Nevada and central Nevada Friday and Saturday. More uncertainty
creeps into the convective potential Sunday into early next week
with just how much moisture may creep into the region as Hurricane
Genevieve brushes the southern tip of the Baja Peninsula.
&&
.FIRE WEATHER...Hot temperatures with light terrain-driven winds are
expected through the week. Near daily chances for isolated
thunderstorms can be anticipated, particularly across the Mojave
Desert and Sierra regions through Thursday. Storms will be capable
of producing strong outflow winds which may aggravate ongoing fire
activity and increase the rate of spread of new fire starts.
&&
.CLIMATE...
DAILY RECORD HIGH MAXIMUM TEMPERATURES
TUE 8/18 WED 8/19 THU 8/20
Las Vegas, NV 111 (1992)* 111 (1992)* 110 (1950)*
Bishop, CA 105 (2001)* 106 (1950) 105 (2015)
Barstow, CA 111 (1992)* 111 (2018)* 109 (2018)*
Needles, CA 115 (2015)* 117 (2018)* 120 (1919)
Kingman, AZ 109 (1915)* 111 (1915) 107 (1915)*
Death Valley 125 (2001)* 124 (1992)* 126 (1931)
DAILY RECORD HIGH MINIMUM TEMPERATURES
TUE 8/18 WED 8/19 THU 8/20
Las Vegas, NV 86 (2018)* 90 (2018)* 89 (2018)*
Bishop, CA 67 (1970) 67 (1961) 65 (1997)
Barstow, CA 80 (2001)* 80 (1973)* 82 (1973)*
Needles, CA 91 (2018)* 93 (2018)* 95 (2018)
Kingman, AZ 80 (2001) 76 (1999)* 80 (2001)
Death Valley 98 (2013)* 99 (2003)* 99 (2018)*
*-Current forecast may be close to current record values.
&&
.AVIATION...For McCarran...Storms south of the valley will likely
create outflow, arriving as southerly winds across valley this this
evening. Winds will then favor typical drainage trends later tonight
with light and variable to easterly winds to start tomorrow. By
Wednesday afternoon, more storms are expected in the surrounding
mountains will be capable of producing gusty, outflow winds in the
valley, even if the storms themselves do not enter the valley.
For the rest of southern Nevada, northwest Arizona and southeast
California...Winds should remain light and follow typical diurnal
trends for the next day or two outside of any thunderstorm outflow.
The Sierra Nevada will continue to support afternoon thunderstorms
with coverage elsewhere, especially in southeast California and
northwest Arizona increasing both this evening and again Wednesday
evening. Gusty and erratic outflow winds around 40 MPH look like for
the Colorado River Valley.
&&
.SPOTTER INFORMATION STATEMENT...Strong wind gusts are likely
today from thunderstorm activity across Northwest Arizona and
along the Colorado River Valley. Spotters are encouraged to report
any significant weather, such as heavy rainfall, strong wind
impacts, or blowing dust according to standard operating
procedures.
&&
$$
DISCUSSION...Pierce
AVIATION...Steele
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