Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/27/21
Area Forecast Discussion...UPDATED
National Weather Service Albuquerque NM
517 PM MDT Wed May 26 2021
00Z TAF CYCLE
Stream of mid to high level clouds over NM at 23Z will gradually
clear from west to east during the next 24 hrs. Dryline stretched
from east of KROW through KCVN and ne into TX where isold strong to
svr tstms with large hail and wind gusts to 50 kts are possible
through 03Z. Dryline to push wwd thereafter to approximately a KROW-
KTCC line by 27/10Z with potential for MVFR cigs along and east of
the line but with conditions improving by 27/16Z. Tstms to develop
along the ern NM/TX border aft 27/20Z then become more nmrs along a
sfc boundary sagging into ne NM aft 27/23Z.
.PREV DISCUSSION...302 PM MDT Wed May 26 2021...
An increasingly active weather pattern is in store through the
holiday weekend as a storm system approaches slowly from the west.
Moisture sloshing around along the Texas and New Mexico border will
shift farther west each day and help set the stage for increasing
coverage of showers and thunderstorms. There is a marginal risk for
severe thunderstorms across all of eastern NM Friday and potentially
again Saturday. The most active period is expected Sunday and Monday
with widespread showers and storms from the central mountain chain
eastward across the plains. Western NM will unfortunately remain dry
and warm through early next week.
SHORT TERM...(TONIGHT THROUGH THURSDAY NIGHT)...
As seen on satellite imagery, mid to high level clouds continue to
stream in across western and central New Mexico thanks to a Pacific
trough. Southwest flow has strengthened today, but winds have
largely been suppressed so far across much of the forecast area
(with the exception of the northeast) due to the cloud cover.
Meanwhile, the dryline is extending from southeast New Mexico into
the Texas panhandle. Even with MLCAPE approaching 1000+ J/kg, LI`s
in the -3 to -4 C range, steep mid-level lapse rates, and 0-6 km
bulk shear approaching 30 kts, weak forcing and a moderate cap has
kept any convection at bay this afternoon. Short term models have
been struggling with the timing and placement of any convection
through the evening, with the HRRR and HREF both showing the
possibility for some discrete to semi-discrete cells sometime
between 23-06z across far eastern Curry and Roosevelt counties.
Models show some clearing in mid to high clouds across western New
Mexico overnight, so lowered minT`s in this area. Further clearing
is expecting on Thursday across the state. By late Thursday
afternoon, an upper-level trough will interact with a backdoor cold
front across northeast NM to produce showers and thunderstorms and
possibly further west along the NM/CO border.
LONG TERM...(FRIDAY THROUGH TUESDAY)...
Friday will begin an extended stretch of very active weather as we
head into the Memorial Day holiday weekend. A convectively-aided back
door cold front is expected to shift southwest across eastern NM
Thursday night and allow moisture to deepen westward to the central
mt chain Friday. Meanwhile, a weak shortwave trough with a 50-60 kt
speed max will eject eastward thru central NM and assist with ascent
and veering wind profiles with bulk shear values near 40 kt over
eastern NM. There will be abundant moisture and instability available
over the region however there are big differences btwn the NAM and
GFS bufr profiles with regard to capping. The 12Z NAM has a stronger
stable layer across the east in the wake of a convective cluster from
Thursday night with only isold storms into Friday night. The GFS and
ECMWF show convective initiation on the Sangre de Cristo Mts Friday
afternoon shifting southeast thru the plains Friday night. SPC still
shows a large marginal risk over eastern NM and the latest NBM PoPs
certainly reflect the more favorable wetter solution.
The pattern is progged to become significantly more active Saturday
as an upper level wave approaches from the west and develops into a
weak closed circulation over southern AZ thru Sunday. This pattern
will assist larger-scale ascent across central and eastern NM with
daily rounds of convection forcing moist outflows westward with each
passing day. PoPs continue trending upward Saturday thru Monday with
much needed moderate to locally heavy precip along and east of the
central mt chain. The threat for strong to severe storms continues
as well with abundant moisture, instability, and lift over the area.
The overall synoptic pattern evolves into a northwest or northerly
flow regime Tuesday and Wednesday with at least scattered storms,
however model agreement deteriorates after Memorial Day.
Locally critical fire weather conditions will continue through the
early evening hours across portions of northeast New Mexico, before
southwest winds subside. Dry conditions continue tomorrow, although
with not as many hours of single digit relative humidity as today
(between 4-14 hours). Showers and thunderstorms will focus across
northeast New Mexico tomorrow, along and behind a backdoor cold
front. The dryline will still be sloshing moisture back and forth
across the NM/TX border each day with better chances for afternoon
showers and thunderstorms Friday through early next week with
excellent overnight humidity recoveries. The dryline may make it as
far west as the central mountain chain at least by Tuesday. It looks
to remain active with daily rounds of showers and thunderstorms
through at least mid-week next week as a Pacific storm system
arrives from the west.
Area Forecast Discussion
National Weather Service Bismarck ND
1013 PM CDT Wed May 26 2021
Issued at 1013 PM CDT Wed May 26 2021
Once again no significant changes were needed to our forecast or
messaging, including to Frost/Freeze headlines which the 01 UTC
NBM probabilities of lows of 32 F or greater still support over
northern ND. A dry slot has moved into southwestern ND as of 03
UTC in advance of the upper-level low that has reached southeast
MT, with the leading edge of precipitation with that wave`s warm
conveyer belt aloft nearing the Missouri River valley. Given the
low freezing levels around 5000 ft AGL on the 00 UTC KBIS RAOB,
bright banding has been obvious on the radar. Still, guidance is
dispersive with its trends in potential for dynamic cooling to
generate snowfall late tonight and Thursday morning, with HRRR
simulations less aggressive than other CAMs and the 00 UTC NAM.
Thus, we will continue mentioning a rain-snow mix, as confidence
in the reasonable worst case scenario -- which would be light to
moderate accumulations on grassy surfaces -- is low, especially
given uncertainty in the intensity of overnight precipitation in
light of the observed mid-evening dry slot. Still, guidance all
suggests precipitation should fill in once again in southwestern
ND after 06 UTC as the main upper-level low reaches the area.
UPDATE Issued at 654 PM CDT Wed May 26 2021
Only minor changes were made to the forecast with this update to
blend observed trends into the early evening, namely refining the
near-term precipitation chances with radar trends through 23 UTC.
Initial precipitation in southern ND is driven by frontogenesis
and midlevel warm air advection downstream of the upper-level low
centered near Billings early this evening. The 00 UTC KBIS RAOB
sampled a dry layer centered around 850 mb, exemplifying the fact
that precipitation will have a difficult time moving north of the
I-94 corridor with dry low-level trajectories emanating from the
surface ridge centered over the northern Red River valley. It is
worth noting that some 12 through 18 UTC global models, and some
CAM cores, are more aggressive with a switch to snow late tonight
and early Thursday morning, especially in the higher terrain to
the west of the Missouri River, e.g., across Morton, Grant, and
Sioux Counties. This would be predicated by dynamic cooling, and
tied to the cold pool beneath the upper-level low. We have some
rain-snow mix mentioned in the forecast, and given uncertainty in
the magnitude of potential dynamic cooling offered by dispersive
model simulations, we will hold with that forecast mix for now.
.SHORT TERM...(This evening through Thursday)
Issued at 308 PM CDT Wed May 26 2021
Precipitation and frost/freeze concerns highlight the short term
This afternoon, a potent mid-level shortwave was exiting the
Northern Rockies with a deepening surface low centered over
eastern Wyoming. Showers driven by increasing DCVA and warm air
advection nosing over western North Dakota were occurring this
afternoon, with more vigorous convection in western South Dakota
feeding off greater MUCAPE.
The aforementioned wave is expected to cross the region tonight
and Thursday, with precipitation likely along and south of the
I-94 corridor. Some light precipitation may be possible up through
the Highway 200 area, but a pretty sharp drop-off in precipitation
totals is likely on the northern periphery of the precipitation
shield. Though subtle differences in placement exist between model
solutions, relatively good agreement exists in rain totals with a
healthy swath of 0.5" to near 1" of rain possible across the
southwest and far south central, with a few isolated areas
receiving more (as depicted by 12Z HREF LPMM). As colder air
filters in the with the low crossing Thursday morning, can`t rule
out some snow mixed in but precipitation should be mostly rain
To the north, a dry air mass and lighter winds should allow good
radiative cooling to bring low temperatures well into the 30s
Thursday morning, with the Bottineau/Rolette area likely falling
below freezing (as further supported by NBM probabilities). The
northern edge of the cloud shield will make a difference as to
frost/freeze potential across the rest of the northern tier of
counties, but there was enough of a frost risk at least to issue
a Frost Advisory across this area, with a Freeze Warning for
Bottineau/Rolette. Further evaluation will be needed tonight with
the potential for any of these areas to fall below freezing
Thursday, precipitation will taper off from northwest to southeast
through the day, with skies clearing in this direction as well.
This will allow the north to warm up the most, with highs near 60
across the north and in the mid 40s across the far south.
.LONG TERM...(Thursday night through Wednesday)
Issued at 308 PM CDT Wed May 26 2021
Frost/freeze will be a concern again Thursday night and Friday
morning, before a warming trend is expected starting this weekend
through the remainder of the forecast period.
Behind the previous exiting low, amplified shortwave ridging will
begin to cross the region early Friday morning ahead of a
progressive Pacific Northwest wave. With the associated surface
high in place, low temperatures will likely fall into the 30s
across the forecast area, with even the NBM 90th percentile
producing lows under 40 degrees. Frost/freeze headlines will
likely be needed given conditions set up as advertised.
Aforementioned Pacific wave enters the region late Friday night and
should cross North Dakota through the day Saturday. Showers are
likely in areas along the associated front, though moisture in the
vertical column will be lacking as the previous shortwave will have
cut-off southerly moisture return. EC/GFS ensemble guidance both
depict just modest chances of exceeding 0.1" of rain, with many
areas likely to see less. In the post-frontal and cyclonic flow
pattern expected Saturday afternoon shallow convection is
possible, thus the area of slight chance precipitation chances
were expanded westward beyond the given NBM probabilities.
After this weekend`s trough, healthy agreement in NBM
probabilities suggest a warming trend for the region as ridging is
forecast to build in the west. CIPS/NBM keep the region dry under
this ridging pattern, as additionally supported by the CPC 6-10
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 1013 PM CDT Wed May 26 2021
MVFR to IFR ceilings initially across southwest ND this evening
will expand into south central ND overnight, and will linger into
midday Thursday from KDIK-KBIS. Rain is likely southwest and south
central roughly along and south of a KDIK-KBIS-KJMS line through
Thursday morning, with a rain-snow mix possible, mainly south of
those terminals. VFR conditions are forecast to continue from
KXWA-KMOT, and will gradually begin to reach the other terminals
after 18 UTC Thursday.
Freeze Warning until 8 AM CDT Thursday for NDZ004-005.
Frost Advisory until 8 AM CDT Thursday for NDZ001>003-009>013.
Area Forecast Discussion
National Weather Service Des Moines IA
640 PM CDT Wed May 26 2021
...Updated 00z Aviation...
.DISCUSSION.../Tonight through Wednesday/
Issued at 355 PM CDT Wed May 26 2021
The primary weather highlight through the period will certainly
be precipitation and severe weather trends late tonight into
Thursday with higher confidence in widespread moderate to heavy
rains, and some severe weather potential but with reduced
confidence in that regard.
Surface pressure falls were already advancing eastward to the MO
River with winds veering with time upstream showing the hand for
strong warm/moist advection into IA overnight and the southwest
corner likely in the warm sector by 12z. Recent convection
allowing model guidance (CAM) is in good agreement with large
scale kinematic and thermodynamic support maintaining a mature
upstream MCS with attendant MCV and potential wind threat across
the forecast area during the early morning hours, and continuing
through the morning commute east with a stronger cluster also into
MO riding the MUCAPE gradient. The inversion and stable layer may
temper the severe wind potential however, especially north and
east. Parameterized and non-parameterized models are all in good
agreement with widespread 0.5-1.5" amounts, with locally higher
amounts possible. Although there has been recent rainfall, it has
not been of the magnitude to make an appreciable drought impact
and reduce long term departures, so RFC contingency forecasts
depict within bank rises, not even reaching Action Stage as of
yet. Recent HRRR runs have also suggested a wake low/gravity wave
potential producing gusty winds behind the convection, which makes
sense considering it will be in the inversion area north of the
Confidence in how Thursday plays out is somewhat lower however.
Recent model trends have suggested a more northerly track with
time, and greater instability into IA south, but the degree of
recovery remains in question after the morning MCS and lingering
debris. Nam and NamNest both seem on the aggressive end of the
guidance and depict a narrow ribbon of 2-3K j/kg MLCAPEs into
south central and southeast sections by afternoon with the leading
edge of that coupled with noted 1km kinematic parameters in low
LCLs resulting in an increased supercellular tornado concern. This
led to SPC nudging the Slight Risk farther north to account for
this possibility. However, looking at the 12Z CAM/HREF guidance,
which includes the NamNest, there is little depiction of
substantial updraft helicities across the forecast area. Thus,
unfortunately, this leaves a spectrum of low confidence
possibilities ranging from little severe weather redevelopment to
discrete tornadic supercells if conditions phase. While not the
most likely solution perhaps, the latter should be noted south and
east as it could potentially affect school dismissal and evening
Any appreciable convection will end by Thursday evening and start
a pattern transition which will still include a few periods of
precipitation but with varied degrees of below normal
temperatures. Confidence in the details will not be great, but
there appears to be a weak long wave trough passage early next
work week which will eventually mature into a more pronounced mean
through through the MS Valley to end the period. Although not to
record levels, this will keep temps cool with low humidities and
little instability. Both kinematic and thermodynamic forcing will
increase late Sunday into Monday ahead of the aforementioned wave.
These low chances will linger into Wednesday as well, mainly
dependent on the GFS which lingers the long wave trough longer
than the EC/CMC solutions.
.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 635 PM CDT Wed May 26 2021
Clear skies will gradually develop high cirrus clouds through this
evening, but will remain VFR. By early Thursday morning, a big
thunderstorm complex is expected to move out of Nebraska and
Kansas. Thunderstorm activity is likely in southern Iowa with
widespread rain showers elsewhere. This will bring IFR ceilings by
Thursday morning and will remain at that through Thursday
afternoon. Expect sudden changes in surface wind direction at
times as this complex moves through. Eventually this big cluster
will move east. More thunderstorm development is possible later in
the afternoon on Thursday, conditional on the preceding storms
clearing in time. Overall, difficult aviation weather conditions
for the latter portions of the 00z TAF period.
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
610 PM CDT Wed May 26 2021
.AVIATION (00Z TAFS)... /NEW/
A fairly common setup is expected for late spring/early summer as
east/southeasterly winds remain somewhat breezy through 03Z before
settling down. All sites should maintain VFR through 03-04Z, before
low level stratus starts to take hold around 04Z-06Z at AUS/SAT/SSF.
An occasional gust to 15-20 kts is possible through 04Z, but will opt
to leave that out of TAFs. MVFR moves in by 04-05Z along the I-35
corridor, followed by a very borderline IFR setup. A bit of a tricky
forecast, but do think winds will be slightly lighter at Austin and
San Antonio, so IFR ceilings are in the forecast from 09Z/10Z until
16/17Z. A quick return to VFR is expected by midday Thursday.
Meanwhile at Del Rio, MVFR ceilings are not expected until after
11Z, with borderline IFR by 12Z. VFR ceilings return by mid to late
morning. One other thing to note for DRT, thunderstorms will try and
organize out west tomorrow afternoon/early evening, and could be in
the vicinity of the terminal by 00Z, however, have opted to hold off
on any mention at this time as confidence is fairly low on timing, so
will let future forecasters assess the potential again at 06Z and
12Z TAF issuance.
.PREV DISCUSSION... /ISSUED 204 PM CDT Wed May 26 2021/
SHORT TERM (Tonight through Thursday Night)...
RAP analysis at 18Z shows a mid-level ridge over Texas. Surface flow
out of the S/SE at 5-10mph has us in a warm, moist environment with
dew points mainly in the low to mid 70s. There`s been more sun
across the Coastal Plains and thus temperatures are already in the
upper 80s there, while most other locations are in the low to mid
80s. Cool spots as usual are Rocksprings and Boerne in the low to
mid 70s as cloud cover has been slow to scatter out over western
portions of south-central Texas. A few very isolated sprinkles were
observed on radar in the late morning. This kind of activity will
remain possible through the afternoon, primarily east of I-35, with
most spots likely remaining dry while a couple locations pick up a
hundredth or two of an inch. Highs should still reach the low to
maybe mid 90s south and west once the sun is able to reach those
areas this afternoon.
Tonight, clouds return late as temperatures drop into the upper 60s
across the Hill Country and low to mid 70s elsewhere. Very similar
conditions expected tomorrow, with clouds scattering out around
midday and highs reaching the mid 80s to mid 90s. Only minor
differences between today and tomorrow are no rain tomorrow and
slightly warmer highs potentially reaching the upper 90s far SW i.e.
across Dimmit/Maverick counties. The mid-level ridge will gradually
flatten and a return to more zonal flow aloft is expected Thursday
night thanks to a shortwave moving through the central Plains.
Modest SSE surface flow will continue and elevated moisture and thus
warm overnight lows will remain in place as we head into Friday
morning. Any convection associated with the shortwave should very
likely remain to our north and west Thursday night.
LONG TERM (Friday through Wednesday)...
With the mid level ridging continuing to weaken as shortwave moves
across the state. The associated front draped from west to east will
be the focus of showers and thunderstorms. The area of better
wide-scale forcing will be to our north, but as storms progress,
chances increase for much of the Hill Country friday afternoon. As
the boundary gets pulled east on Saturday, convective outflow
boundaries residing in the area, along with west to east moving
dryline will be more areas to watch for development.
Mid level ridging gains control again for Sunday and Monday, leaving
a dry forecast for most of the region. Still, dryline and the general
troughing to the west will need to be monitored for any initiation
of convection in our western counties.
Entering midweek, the pattern becomes more unsettled. By Tuesday, a
deepening trough to our west glides east and envelopes the State.
Multiple disturbances in this flow will further aid in the
development of convection across the region.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 87 71 87 72 87 / 10 - 0 - 30
Austin Bergstrom Intl Airport 87 71 87 72 87 / 10 - - - 30
New Braunfels Muni Airport 88 72 90 74 89 / 10 - - - 20
Burnet Muni Airport 87 69 87 71 85 / - 0 0 10 40
Del Rio Intl Airport 93 74 96 76 96 / 0 0 0 - 20
Georgetown Muni Airport 86 71 87 71 86 / - - 0 - 40
Hondo Muni Airport 90 72 92 72 90 / - 0 0 - 20
San Marcos Muni Airport 87 71 88 72 88 / 10 - - - 20
La Grange - Fayette Regional 88 73 89 74 88 / 20 - 0 0 30
San Antonio Intl Airport 88 73 90 73 88 / 10 - - - 20
Stinson Muni Airport 89 73 91 74 91 / 10 - - - 20
Area Forecast Discussion
National Weather Service Indianapolis IN
1128 PM EDT Wed May 26 2021
...Updated Aviation Discussion...
Issued at 930 PM EDT Wed May 26 2021
Surface analysis this evening shows a secondary cold front stretching
across central Indiana...a spoke within a deeper system connected to
stronger low pressure over Quebec. High pressure was found across
Central Canada...providing a northerly flow of air to the Great
Lakes. Low pressure coming out of the Rockies was resulting in
convection across the Western plains. GOES16 showed clear skies
across Indiana as well as Illinois.
The cool front across the area is expected to depart overnight while
the high pressure system to the north continues to provide a cooler
flow of air on northerly winds. Dewpoints upstream were in the lower
50s...and with clear skies expected though the night...have trended
low slightly cooler than the previous forecast. Otherwise forecast
in good shape with mostly clear skies expected.
.Short Term...(This evening through Thursday night)
Issued at 302 PM EDT Wed May 26 2021
Showers from earlier in the day have exited the area, although cloud
cover lingers across much of the area. It has, however, thinned out
a bit across the northwestern half of the area in the last couple of
While isolated convective showers/perhaps a storm cannot entirely be
ruled out across the southeastern portions of the area as the
surface front moves through late this afternoon into the evening,
limited instability due to the lingering cloud cover along with weak
midlevel subsidence in the wake of the leading trough appear likely
to significantly limit this activity. CAMs support this idea and
have been trending drier and further south with late afternoon
activity through the day. Will maintain low chances in the southeast
this afternoon, tapering to a dry forecast at 00Z. Skies will clear
somewhat overnight before mid and high cloud begin to move back in
late tonight into Thursday ahead of our next system.
The majority of precipitation and thunderstorm activity looks likely
to hold off until after 00Z Friday, although cannot entirely rule
out some showers or storms sneaking into our west late tomorrow
afternoon. For most of the area, however, a lingering capping
inversion around 750-800mb should keep a lid on convective activity
much if not all of the daytime hours tomorrow, with the remnants of
stronger upstream convection moving into the area Thursday evening
into the overnight.
Given this unfavorable timing diurnally, while shear will be
adequate, instability will be fairly modest, and forecast profiles
are more pseudotropical in nature, with model precipitable water
values nearing climatological maximum, suggesting more of a hydro
threat than severe, and indeed see the day 2 severe outlook has
pulled the slight risk west and out of the area. Marginal remains
reasonable as convection could potentially still be somewhat strong
but weakening as it moves into the area, but severe threat again
looks to be limited. Marginal to slight risk in the day 2 excessive
rainfall outlook is well placed.
.Long Term...(Friday through Wednesday)
Issued at 302 PM EDT Wed May 26 2021
Models in good agreement that a frontal system will move southeast
across central Indiana Friday as an upper trough follows Friday
night. The surface low will be near west central Indiana 12z Friday
and southeastern Indiana around 18z. The frontal forcing, deep
moisture, including 30 knot low level jet, moderate mid level winds
and sufficient instability with ML CAPEs 200-400 J/kg support
widespread showers and thunderstorms Tuesday morning. Chances will
be dropping off from northwest to southeast Friday afternoon and
evening in the wake of the cold front.
Precipitable water amounts over 1.5 inches supports potential for
heavy rain and the combo of moisture, forcing and instability
justify the Marginal Risk for severe weather from SPC.
Big changes in store for the weekend. Aside from a dry airmass, cool
Canadian high pressure will bring much cooler temperatures to the
area. With Low level 850 millibar thermal progs coming in at only 4
degrees Celsius and decreasing cloud cover, temperatures will only
reach the lower 60s at best. Then, near full sunshine and veering
low level winds should allow temperatures to return to the lower 70s
Sunday. The next chance of unsettled weather will return early to
middle parts of next week as a system sets up over the Plains and
high pressure shifts to the Appalachians and east coast.
.Aviation...(06Z TAF Issuance)
Issued at 1127 PM EDT Wed May 26 2021
- VFR Conditions are expected the next 2-4 hours.
- Patchy IFR fog possible overnight at BMG from 10Z-12Z.
- A return to VFR everywhere after 2713000Z.
- SHRA with MVFR Cigs will be possible after 280000Z.
DISCUSSION: GOES16 shows clearing skies building across the Central
Indiana TAF sites. Forecast soundings and time heights suggest
subsidence through the night. Lingering higher dew points at BMG in
combination with recent rains may result in some IFR fog overnight
at BMG. Thus have used a tempo group to account for this for now.
As heating and mixing resumes on Thursday...a quick return to VFR at
all sites is expected with increasing high clouds through the course
of the day as a warm front approaches from the west. Convective
temperatures in the lower 80s suggest the development of some sct
VFR CU in the afternoon.
As a warm front and a low pressure system arrive in Indiana after
00Z...light rain along with MVFR Cigs will be expected. HRRR
suggests best chances at HUF and BMG...with lesser chances to the
north. Forecast soundings overnight also suggest deep
saturation...but with minimal instability. Thus have left thunder
out for now.
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1102 PM CDT Wed May 26 2021
Issued at 936 PM CDT Wed May 26 2021
Only minor tweaks to the forecast this evening. Some 00Z model
guidance is rolling in already and it still looks like there will
be two waves of convection to affect the area tomorrow. The first
will be whatever develops out in the Plains tonight, and the
second will be ahead of the cold front late Thursday
afternoon/evening. There are still so many ways this could happen
though, and there are timing and strength differences between the
latest CAM guidance. The newest deterministic RAP shows plenty of
instability ahead of the first wave of convection in the morning
and early afternoon for strong/severe storms...as much as 3500+
J/Kg SBCAPE, and it shows the atmosphere recovering quickly behind
the first wave and ahead of the cold front. This seems to agree
with most of the latest CAMs which develop more strong convection
in this unstable air ahead of the front. Of course, the
aforementioned timing issues will have a great impact on how
strong the evening convection can ultimately become. With all this
in mind, I see no reason to adjust our expectations for
potentially severe storms on Thursday.
.SHORT TERM... (Through Late Thursday Night)
Issued at 216 PM CDT Wed May 26 2021
A very weak cold front is sliding through central Missouri and
southern Illinois, its passaged marked by a wind shift and slight
decrease in dewpoints. It will continue to progress southward during
the afternoon, eventually stalling near the Missouri-Arkansas
border. This boundary will start moving northward overnight as a
warm front, bringing a surge of warm, moist, unstable air back to
the region for Thursday.
The main focus of the short term has shifted to severe chances on
Thursday. The situation has evolved into two MCSs moving through the
mid-Mississippi Valley. While the second MCS is the system of
concern, it will be influenced greatly by the movement and
characteristics of the first MCS.
An MCS is expected to form this afternoon/evening across central
Nebraska, charging eastward overnight and moving through Iowa and
northern Missouri during the early morning hours of Thursday.
Instability will be modest, between 500-1000 J/kg of MUCAPE as this
MCS moves into the northern portion of our forecast area tomorrow
morning. The main threats from this complex will be strong winds,
small hail, and locally heavy rainfall. The southern extent of
this complex and the location of the cold pool boundary will
determine how much instability is available during the afternoon
for the second, more southern MCS to tap into. There is little
consensus in guidance on these features, some sources keep the
first MCS north of the St. Louis metro and others bring the MCS
through the metro during the afternoon. While these differences
matter, what guidance does highlight is that central and
southeastern Missouri will be largely unaffected by the passage of
the first MCS. These areas will have benefited from WAA and
increased instability south of the northward advancing warm front.
Wherever the cold pool boundary stalls will then be the focus for
severe storm development later in the day.
A second MCS will form in association with a surface low swinging
through the region along a mid-level trough, and slide through
central Missouri into southern Illinois during the afternoon and
evening. This second MCS is anticipated to track along the outflow
boundary from the first MCS, and will be the area of greatest
concern for severe weather. As mentioned earlier, there is
uncertainty in where the cold pool boundary will develop and linger.
MUCAPE values between 1000-2000 J/kg and 0-6 km shear between 30-40
kts will create a favorable environment for severe thunderstorms to
produce damaging winds and a few tornadoes. The potential
hydrological impacts from these two thunderstorm complexes is
discussed below in the Hydrology section.
By overnight Thursday a strong cold front associated with the
surface low will push convection southeastward out of the area,
bringing cool, dry, stable air to the region. Temperatures
Thursday night will cool into the low 50s across northeast
Missouri to the low 60s across southeast Missouri and southern
.LONG TERM... (Friday through Next Wednesday)
Issued at 216 PM CDT Wed May 26 2021
1. The holiday weekend continues to look cool and dry under the
influence of a robust anticyclone over the Great Lakes.
2. The region will return to a warm, active pattern early next week.
Driven by a mid-level trough swinging through the Upper Mississippi
Valley, a cold front will drop through the region Friday in the wake
of Thursday`s systems, bringing an end to the rain chances for a
couple of days. Deep northwest flow behind the cold front will bring
850 temperatures 1-2 standard deviations below normal surging
into the forecast area on Friday. The robust CAA will cool surface
temperatures Friday into the low 60s in northeast Missouri and
west- central Illinois to lower 70s across southeast Missouri.
A mid-level ridge will build into the Upper Plains behind the low
Friday and Saturday, reflected at the surface by a high that will
deepen over the Upper Plains/Great Lakes regions. The anticyclone
and dry northwest flow will keep Memorial Day weekend dry, which is
reflected in the WPC Cluster Analysis and the QPF from GEFS and
ECMWF ensemble members. A mostly clear sky and dry conditions will
help temperatures moderate through the weekend from their chilly
conditions on Friday.
By early next week the mid-level ridge will retreat eastward, pushed
by a trough advancing into the region. The movement of the trough
will return the region to southwest flow aloft and a more active
pattern, bringing rain chances back to the region. While operational
guidance isn`t in agreement about the details of the trough`s
position, amplitude, or timing, WPC Cluster Analysis and ensemble
member QPF indicate rain chances will return to the region as
early as Memorial Day. While an isolated shower or two is possible
Memorial Day, there will be plenty of dry time. The return to
active flow will also mean a return to summer-like conditions,
with temperatures peaking in the mid to upper 70s.
.AVIATION... (For the 06z TAFs through 06z Thursday Night)
Issued at 1055 PM CDT Wed May 26 2021
VFR flight conditions are expected to prevail for the remainder of
the night. Guidance continues to show a complex of thunderstorms
moving into central and northeast Missouri and west central
Illinois after 12Z Thursday morning. Timing and strength
differences continue in the guidance, but the storms will likely
produce intermittent IFR visibility and gusty winds. Lower
confidence forecast continues after 15-18Z, though the latest
guidance shows a stronger complex of storms moving across the
entire area through the day. Models are showing more storms
developing ahead of the cold front across west central into
central Missouri after 22Z. The development of these storms will
be conditional on enough instability redeveloping in the wake of
the first round of storms.
SPECIFICS FOR KSTL:
VFR flight conditions are expected to prevail at Lambert into
Thursday morning. A complex of thunderstorms is expected to move
into central Missouri after 12Z Thursday, and continue east
through the morning. Latest guidance shows storms will maintain
strength and probably bring heavy rain, IFR visibility, and gusty
winds to the terminal between 18-21Z. Another round of strong
storms may develop ahead of a cold front after 00Z Friday, but
this will be contingent on whether enough instability can
redevelop in the wake of the first round of storms.
Issued at 314 AM CDT Wed May 26 2021
Two large thunderstorm complexes are expected to move through the
region on Thursday. Both MCSs will be able to tap into the
1.5-2.0" of precipitable water that will surge northward into the
region along stout southerly flow to produce 1-2" of rainfall
across the region. Multiple rounds of thunderstorms, well above
average atmospheric moisture, and the potential for training
thunderstorms could produce locally higher amounts and localized
flash flooding. As the details of these two systems come into
greater focus tonight and tomorrow morning, so too will details on
the flooding potential across the region.
Area Forecast Discussion...UPDATED
National Weather Service Memphis TN
927 PM CDT Wed May 26 2021
A few showers remained east the Natchez Trace in northeast MS at
midevening, but were slowly dissipating. With sunset and the
departure of clouds to the north, visibility at Lexington-Parson
(KPVE) dropped to a half mile in the last hour, while Savannah
(KSNH) visibility dropped to 1 1/2 mile.
Some upstream convective debris clouds will flow in from the
central plains storms overnight, not likely sufficient to
preclude fog formation that was already underway near the TN
River. Latest runs of the HRRR model depict dense fog developing
over most of west and areas of MS north of Tupelo overnight, where
9 PM dewpoint depressions were already 2 degrees or less. With
this in mind, a Dense Fog Advisory has been issued, in effect from
10 PM to 9 AM. Went fairly conservative on areal outline, following
HRRR guidance and with deference to upstream clouds over MO. The
advisory may be expanded as needed later tonight.
.PREV DISCUSSION... /issued 642 PM CDT Wed May 26 2021/
See the 00Z aviation discussion below.
PREV DISCUSSION... /issued 257 PM CDT Wed May 26 2021/
A shortwave continues to move east across the Mid-South this
afternoon. As a result, showers continue across areas of West
Tennessee near the Tennessee River and Northeast Mississippi.
The convection will continue to push east over the next couple of
hours and should exit the region by sunset. Meanwhile, a few
spotty diurnal showers are also beginning to develop near the
MO/AR state line. These showers will dissipate by sunset as well.
Thereafter, expect tranquil conditions through the overnight
period other than some possible fog development.
Tranquil conditions will continue until Thursday afternoon, when
isolated to scattered thunderstorms will begin developing across
Northeast Arkansas and the Missouri Bootheel ahead of an
approaching cold front. Better chances for showers and
thunderstorms will then come later in the evening into the
overnight hours as a MCS is expected to develop over Missouri and
move southward through the period. Exact timing of the MCS remains
in question based on latest CAMS. Some models move it into
northern portions of the Mid-South earlier in the evening which
would mean increased chances that the line would be severe. Other
models show the line moving into the area well after midnight. If
the line moves in after midnight, the severe threat would likely
be limited due to decreasing instability across the region.
Whatever happens Thursday Night will set up initiation for
thunderstorm development on Friday. Looking at the 3KM NAM and
FV3, initiation may occur across Northeast Mississippi during the
afternoon as the front or old outflow boundaries from Thursday
Night`s convection may sink that far south. These storms will
capable of becoming strong to severe as well.
High pressure will then begin to build into the area Friday Night
into the weekend. Have trended cooler with temperatures based on
latest guidance. Expect highs to range from the upper 60s to upper
70s while lows will range from the upper 40s to upper 50s.
Dry conditions will continue into Memorial Day with highs expected
to climb into the upper 70s to mid 80s as upper ridging begins to
occur over the area.
Confidence in forecast begins to dwindle by Tuesday and Wednesday
as an upper trough will begin to move into the Central and
Southern Plains. How far east it moves will depend on how strong
the ridge is. Will continue with 20-30 POPS due to the Mid-South
being in the transition zone between the ridge and the upper
Generally VFR conds through the period. Winds will go light and
variable overnight, with fog possible at MKL and TUP. Conds could
fall as low as IFR/LIFR at those sites. All sites will return to
VFR by 27/15Z.
A few isolated SHRAs or TSRAs are possible tomorrow afternoon,
but confidence is too low to add to any TAF sites at this time.
Expect southwest winds 8-12 kts with gusts to 16kt tomorrow
afternoon at western sites. A complex of SHRAs and TSRAs will
move into the region around midnight tomorrow night.
MS...Dense Fog Advisory until 9 AM CDT Thursday for Alcorn-Benton MS-
TN...Dense Fog Advisory until 9 AM CDT Thursday for Benton TN-Carroll-
AREA FORECAST DISCUSSION
National Weather Service Charleston WV
843 PM EDT Wed May 26 2021
Showers and storms accompany a mid level disturbance through
this evening. Wet Spring storm system Friday with cool and wet
conditions lingering into the start of the weekend.
.NEAR TERM /THROUGH THURSDAY/...
As of 558 PM Wednesday...
Sent a quick update to remove thunder across the western half of
our CWA for the rest of the afternoon, as radar imagery suggest
disorganized rain showers diminishing in intensity. Isolated
thunderstorms are still occurring across the eastern third
including the mountains, but are expected diminish or dissipate
by sunset. Rest of forecast remains on track.
As of 125 PM Wednesday...
Shower and thunderstorms activity is expected to continue to
increase this afternoon as the surface continues to warm. Cloud
layer shear and mid-level lapse rates are rather marginal, perhaps
25KTs and 6C/km H700-H500, but should still be able to generally
perhaps a grand of MLCAPE with temperatures in the mid to upper 80s
and dew points in the lower 60s. With rather steep low level lapse
rates with the aforementioned strong surface heating, the main
threat will be localized damaging wind gusts beneath the
stronger cores and perhaps some marginally severe hail.
Precipitation coverage will increase late this afternoon into this
evening as a pre-frontal trough provides a focus for ascent.
This should provide a relatively narrow window for a better
organized line of convection, mainly for the northwestern half
of the forecast area late this afternoon into early this evening
with a few instances of damaging wind possible. As the line
progresses further southeast, instability will begin to fade
with loss of heating and would expect any activity to taper off
to showers by the early overnight.
The cold front arrives late tonight, stalling W-E roughly bisecting
the forecast area by early Thursday morning. Will likely see
plentiful low stratus Thursday morning where the front stalls, along
with at least some patchy river fog. Could see a bit more widespread
fog Thursday morning if skies clear out more than anticipated.
Thursday will be a quieter day with the cold front sinking south of
out of the forecast area by midday. Couldn`t rule out a stray
shower across S WV or S VA in the afternoon, but the bulk of the
region will remain precipitation free.
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 246 PM Wednesday...
A few isolated showers and storms will be possible Thursday night as
a surface low in the Midwest pulls a warm front northward through
the area, but any activity should be elevated. The higher chance of
more widespread convection will occur Friday afternoon and evening
as the surface low moves across the Ohio Valley and drags a cold
front across the region. Latest SPC Day 3 Convective Outlook has our
entire area in a Marginal risk on Friday as 0-6 km shear values of
35-40 kts are expected to be in place, but how much instability is
realized is still somewhat uncertain. While models such as the NAM
and RAP do suggest that SBCAPE values may reach about 2000 J/kg, the
GFS has much weaker instability parameters as there is
uncertainty in the amount of clearing that could occur.
Regardless, damaging winds will be the primary threat with the
widely scattered convection, but large hail could also occur,
especially if enough instability materializes. In addition,
with PWATs surging to values of 1.8 inches ahead of the cold
front, some localized flooding issues could develop. Rainfall
amounts in general should be about an inch through Friday night
for many areas, but locally heavier amounts of 1.5 to 2 inches
will be possible in areas where heavier embedded storms develop.
While the majority of the precipitation should taper off by
Friday night as the cold front and surface low push east of the
region, isolated to scattered showers are expected to linger on
Saturday as the supporting upper trough slowly approaches. This
activity should be light and showery in nature with most areas
expected to receive a tenth or less of precipitation through
Saturday evening. Otherwise, it will be much cooler on Saturday
with highs about 10 degrees below normal in the showery and
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 246 PM Wednesday...
Additional showers will remain possible Saturday night into
Sunday as the aforementioned upper trough continues to slowly
swing through the region, but overall QPF amounts should
continue to remain light. Otherwise, temperatures on Sunday
should be about 5 degrees warmer than Saturday in most areas,
but likely remaining below normal.
Surface high pressure should provide dry conditions for early
next week, but precipitation chances may increase by midweek as
the GFS shows a coastal system developing near the southeast US
and the moisture associated with this system gradually building
towards our area. However, the ECMWF shows the next system
generally approaching from the west and a more zonal flow aloft
but the general trend is for a return of PoPs by the end of the
long term period. In addition, temperatures should return to
normal values by Monday and are expected to gradually rise to
above normal values through midweek.
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 843 PM Wednesday...
Radar imagery indicate that showers and storms have dissipated
or moved east northeast away from the area. Additional light
showers remain over northeast KY, expected to move over WV this
evening. Expect a continuation of VFR conditions outside any
lingering showers through at least midnight. Terminals that
received rain this afternoon could develop a low ceilings before
midnight. Then, areas of dense fog are anticipated over areas
that received rainfall and along river valleys. Fog development
will depend on how much skies clear tonight.
A cold front digs south overnight, stalling south of the region
Thursday. This feature could promote MVFR/IFR low status
development tonight. There could be a battle between the
development of low stratus and dense fog into Thursday morning.
Thinking stratus may be more prevalent than fog, but do have
some IFR visibility restrictions at the end of the period.
Northwest winds decreasing to 10KTs this evening before going
calm during the latter half of the overnight.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z FRIDAY...
FORECAST CONFIDENCE: Medium.
ALTERNATE SCENARIOS: Fog could be more dense if skies clear
than more advertised by Thursday morning.
EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
DATE THU 05/27/21
UTC 1HRLY 00 01 02 03 04 05 06 07 08 09 10 11
EDT 1HRLY 20 21 22 23 00 01 02 03 04 05 06 07
CRW CONSISTENCY H H H H H H H H M H H M
HTS CONSISTENCY H H H H H H H H M M M M
BKW CONSISTENCY H H M H H H M M M M M L
EKN CONSISTENCY M M M H H M M H H H M L
PKB CONSISTENCY H H H M M M H M H H L L
CKB CONSISTENCY H H H H H H H H H H H H
AFTER 00Z FRIDAY...
IFR possible in rain on Friday.