Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/29/21
Area Forecast Discussion
National Weather Service Buffalo NY
1048 PM EDT Wed Jul 28 2021
High pressure across the region will maintain dry weather overnight.
Then, a cold front will bring a chance for showers and thunderstorms
Thursday, with some showers possible through Friday morning. Cooler
weather will prevail Friday and Saturday as high pressure builds
back across the area.
.NEAR TERM /THROUGH THURSDAY NIGHT/...
High pressure crossing New England will provide fair weather
overnight. Mostly clear skies at present will give way to mid
and high clouds overnight spreading from west to east across
the area. The coolest temperatures will be east of Lake Ontario,
since this is where clear skies will last the longest.
A mid level trough will dig across the region on Thursday, which
will lead to increasing chances for showers and possibly a
thunderstorm. A complex surface map, with majority of guidance
bringing a convectively generated wave across Ohio which may clip
part of the area Thursday morning. Majority of 12z high res guidance
in the HREF suite and recent runs of the HRRR indicate remnants of
this convection could follow H85-H3 thicknesses/edge of higher
instability and move into southwest NYS by 12-13z/8-9 AM. Upscale
convection has developed last couple hours over upper Lakes, but
based on where most vigorous convection is attm, think stronger part
of this line of storms may end up staying well to west of our area
as it heads more south-southeast into better instability.
However, showers and some embedded thunder are quickly spreading
into eastern Upper Michigan and northern Lower Michigan. Starting
to think this activity, at least in diminishing form, tied to
leading shortwave may be what models show moving into western NY
on Thursday morning. Radar trends overnight will hold key for
how convection evolves over our region on Thursday. Though
diurnal heating may support some instability with showers and
possibly a thunderstorm on Thursday, more likely than not, any
severe weather would remain to our south, with most recent SPC
day2 outlook keeping the marginal risk just south of the NY/PA
There may be some lake/upslope enhanced showers south of the
lakes Thursday night. Otherwise, temperatures will average below
normal with highs in the 70s on Thursday and lows in the mid
50s to around 60 on Thursday night.
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
With 850mb temps dropping into the 6-7C range by Friday morning,
some pesky lake effect/upslope rain showers will linger through the
morning. Surface high pressure then builds into the central Great
Lakes by afternoon, with associated subsidence bringing an end to
any leftover showers and giving way for a dry afternoon. Though the
summer sun will be shining, temperatures will be about 10 degrees
below average, with highs around 70 across lower elevations and mid
60s for higher terrain.
High pressure centered over the Ohio Valley and central Great Lakes
Friday night will maintain dry conditions and northwest flow across
our region. Some lake effect clouds may develop southeast of the
lakes overnight, but low inversion heights should prevent any lake
effect rain showers. Overnight temperatures will fall into the low
to mid 50s across the lake plains and mid/upper 40s for the interior
Southern Tier and North Country.
The upper level pattern across North America will continue to
amplify moving into the weekend, with a sharp ridge axis centered on
the Rockies and an unseasonably deep downstream longwave trough in
eastern North America. This will keep temperatures below average
over the weekend. High pressure shifts eastward across NY/PA
Saturday, maintaining dry weather through the day. Rain chances
increase from northwest to southeast Saturday night as a shortwave
rounds the base of the longwave trough, bringing with it an area of
surface low pressure across the Great Lakes and New England. Extra
cloud cover late Saturday night will help moderate overnight
temperatures some, with lows in the low 60s and upper 50s across the
Lake Plains, with low to mid 50s elsewhere.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Strong consensus that vigorous shortwave will drop across Lower
Great Lakes on Sunday. Have bumped pops to high likely for showers
and possible thunderstorms...very unsettled to end the weekend.
Temps to struggle to get out of the 60s.
Showers wind down in coverage Sunday night as shortwave exits across
srn New England.
While leftover showers will be possible across the North Country
early Monday...large sfc high should promote fair dry weather Monday
through Wednesday. Temps will slowly moderate through the
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
High pressure will provide mainly VFR flight conditions overnight.
Mid-level clouds will move in which will diminish the potential for
fog across the Southern Tier. Showers will spread into the area
Thursday morning, with possibly a thunderstorm. Increasing moisture
will lead to lowering cigs with MVFR possible at KJHW by Thursday
Increasing chances for showers and possibly a thunderstorm Thursday
afternoon, with MVFR cigs.
Thursday night...lowering cigs with IFR/MVFR restrictions.
Friday...MVFR/VFR. A chance of showers with lingering clouds
south of the lakes.
Sunday...MVFR. Showers likely.
SCA conditions not expected until Thursday night into Friday, due to
the passage of another cold front. Lake temp/850mb delta Ts increase
to 15C late Friday and Friday night, but relatively low equilibrium
level suggest a low but non-zero risk for waterspouts during that
time period. Confidence too low to include in the forecast for now.
Area Forecast Discussion
National Weather Service Quad Cities IA IL
559 PM CDT Wed Jul 28 2021
...00z AVIATION UPDATE...
Issued at 235 PM CDT Wed Jul 28 2021
Very warm and humid conditions were observed early this
afternoon. Well advertised heat has been verifying, with heat
indices above 100 degrees at most locations. Dewpoints were in the
middle to upper 70s, with a few AWOS sites which are known to
have a wet bias with dewpoints reporting lower 80s. High level
clouds may have dampened the heat potential some across the north,
but it is still very hot outside.
Several strong thunderstorms developed along a persistent 850-750mb
mid-level boundary over northwest and northern IL this morning, some
of which produced small hail, frequent lightning, and heavy
downpours in Whiteside, Henry, and Bureau counties in IL. As of 2 pm,
the warm temperatures aloft have kept a lid on any convection
over most of the CWA. However, starting to see some Cu fields to
develop close to our area on visible satellite.
.SHORT TERM...(This Evening through Thursday)
ISSUED AT 235 PM CDT Wed Jul 28 2021
Forecast focus in the near term is on the heat.
Will continue the heat advisory through 10 pm tonight across our
northern counties and maintain the other areas through 8pm Thursday.
Dewpoints will remain in the 70s through the overnight hours,
keeping heat index values above 75 degrees, making for a rather
uncomfortable night outside. Attention then turns to the evolution
of severe storms across MN/WI this evening. Most model guidance now
keeps this activity to the northeast of our CWA, so am expecting a
quiet night through midnight if not later. Kept some slight chance
PoPs over our far northeast counties to account for any outflow
boundary making its way into our area early Thursday. Forecast
soundings and RAP severe progs depict substantial CAPE values in the
1800-2000 J/Kg range, 45kts of 0-6 km shear, and PWs approaching 2"
so any storm that does reach our area, will bring a threat of
damaging wind and heavy rain. Overnight lows will only drop in the
low to mid 70s.
Thursday...a weak cold front will track through the CWA between 10-
16z before stalling out near the IA/MO border. Winds will shift to
the north and bring a nice breeze to dampen the heat some,
especially across the north. Convergence along this front is really
weak, so anticipating little if any storm development until the
afternoon hours in our southern third of the CWA. This is also where
the heat/instability will build through the day and where there is a
marginal risk for severe weather per SPC Day 2 outlook. Dewpoints
will once again reach the low to mid 70s along and south of I-80 and
combined with temperatures rising into the lower 90s, will result
in heat index values above 100 degrees in the afternoon. Be sure
to take frequent breaks and stay hydrated when working outside.
Highs will be a few degrees cooler than today, with readings in
the upper 80s north and lower 90s south.
.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 235 PM CDT Wed Jul 28 2021
1) Warm and quiet weather continues through the beginning of the
period, with potential for showers and storms returning Saturday.
2) Ridge builds in the west, putting us in a strong northerly flow,
resulting in much cooler temperatures than we have seen as of late.
Friday Through Sunday...
Ridge in the west stays in place and continues to build through
Sunday, leaving us in an upper level northwest flow regime. Winds as
we get closer to the surface are generally from the west, shifting
to a low level northerly wind on Saturday. This will help to keep
the humidity a little lower than we have seen as of late, with
dewpoint temperatures in the mid to upper 60s. Latest guidance
continues to introduce a weak wave moving through Saturday evening
and into Sunday, bringing a surface cold front through. Where
confidence is lacking is the timing (slightly) and the overall
coverage of precipitation, with latest trends pushing chances a
little farther north. While precipitation is possible, widespread
heavy rainfall isn`t expected at this time. The southern parts of
our forecast area have been the targeted area for best chances to
see precipitation over the last few forecast runs, which continues
to be seen. Temperatures will be near normal at the start of the
period, trending slightly below normal through the remainder of the
weekend, especially after frontal passage. This will bring much
needed relief to the area, with daytime temperatures in the upper
70s and low 80s and nighttime temperatures in the 50s and 60s.
The building ridge will hold strong through the first part of next
week, leaving us in a northerly flow. This, coupled with the post-
frontal airmass, will lead to a pleasant start to the week.
Temperatures will feel much cooler than they have been, with
widespread 70s and low 80s and dewpoint temperatures may also be in
the 50s for some. This will continue through Tuesday. Wednesday,
long term guidance indicates that the ridge will begin to slowly
break down, but a newly developed cut off upper low will aid in
keeping us in a relatively light northerly flow aloft. While that is
the case, low level return flow will also commence. This will lead
to increasing moisture and temperatures through the area. With the
gyrating low to our east and increasing moisture and temperatures,
we may see some chances for isolated to scattered showers to storms
for the second half of next week.
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 558 PM CDT Wed Jul 28 2021
VFR conditions will prevail for all terminals for this TAF period. A
cold front is progged to move from north to south across the area
late tonight and Thursday, which will result in a gradual wind shift
from southwest to northwest. A low-level jet is forecast to
develop ahead of the front just ahead of the front, which will
result in a brief period of LLWS for KCID, KDBQ and KMLI Thursday
morning. A scattered shower or storm will also be possible ahead
of the front late tonight, but confidence is low as guidance is
not in good agreement of impacts to the terminals. Have left
mention out at this time, but this will be monitored for future
IA...Heat Advisory until 10 PM CDT this evening for Benton-Buchanan-
Heat Advisory until 8 PM CDT Thursday for Cedar-Des Moines-Henry
IL...Heat Advisory until 10 PM CDT this evening for Bureau-Carroll-Jo
Heat Advisory until 8 PM CDT Thursday for Hancock-Henderson-
Henry IL-McDonough-Mercer-Rock Island-Warren.
MO...Heat Advisory until 8 PM CDT Thursday for Clark-Scotland.
Area Forecast Discussion
National Weather Service El Paso TX/Santa Teresa NM
605 PM MDT Wed Jul 28 2021
.AVIATION...00Z TAF CYCLE
VFR conditions are expected across all TAFs sites with ceilings
SCT-OVC100 SCT-OVC250. VIS may temporally reduce to less than 10SM
at KELP and KTCS between 01 and 03Z due to showers and
thunderstorms in area. The winds will be generally from the
northeast to the southeast at both KELP and KLRU between 10 and
20KT with gust up 30KTS. However, the winds at KTCS and KDMN will
be generally from the northwest to the southwest between 10 and
20KTS with gust up to 30KTS. Not expecting any TS across the KDMN
and KLRU; however, there is a chance for TS across the rest of the
sites before 04z. The rest of the period will be relatively quiet
with no reduction in VIS on the runways.
.PREV DISCUSSION...236 PM MDT Wed Jul 28 2021...
Active weather continues over the next seven days. Scattered
showers and thunderstorms are expected over the mountains, and
isolated storms over the lowlands. There will be less activity in
the next few days, but coverage increases late this weekend and
early next week. The reason will be the approach of a backdoor
cold front that will push moisture towards the Borderland on
Sunday night. The moisture remains through at least the middle of
next week. Temperatures remain at or slightly below normal.
.SHORT TERM...Tonight and Thursday...
East flow aloft tonight with some embedded energy in addition to an
influx of moisture will result in the potential for some light
showers or tstorms across portions of the area. HRRR appears to show
a boundary popping said convection right over the Rio Grande. As
such, have low end pops, but not expecting anything of significant
Similar conditions expected on Thursday, with above normal PW,
especially out west. However, dewpoints will top out in the lower
50s during the afternoon it seems, fostering only modest CAPEs of
~500j/kg, to up to 1000j/kg across far western areas. As a result,
terrain and west of the continental divide will be the focus, with
isolated popcorn storms elsewhere across much of the lowlands. Area
of enhancement will be across the Gila, with locally heavy rainfall
the primary threat. There`s some ""mildly"" enhanced flow aloft
across the northern portions of the CWA, so I suppose a stronger
storm or two cannot be ruled out, especially in the Gila.
Temperatures through the period will be be seasonable and winds
light to mildly breezy, 10 to 20 mph with a few higher gusts in
select areas as the east moving boundary moves through tonight.
.LONG TERM...Friday through Tuesday Night...
Elongated upper high tilted from NW to SE from the Front Range to
the Gulf States persists on Friday. This orientation allows an
inverted trough to ascend from Mexico towards Arizona. The deep
core of the moisture plume appears to remain over AZ. Thus, we
have another day with convection starting over area mountains with
a few storms moving over the lowlands later in the afternoon and
evening. This weekend, the upper high backtracks towards the
Central Rockies. Usually this would mean warmer temperatures and
drier weather. However, the decent moisture content across the
area, precipitable water ~1.2 inches and sfc dewpoints between 45
to 55F will keep slightly below normal temperatures and wetter
conditions. The environment will also be marginally unstable, so
storm chances don`t go away. The main hazard with any storm will
be periods of heavy rain. Areas where the ground is saturated from
the rain over the past couple of weeks, may experience minor
Early next week, the upper high remains over the Rockies. However,
a new feature comes into the forecast. A backdoor cold front moves
over on Sunday night into Monday morning. Temperatures further
drop with the advection of colder air, but stay around 5 degrees
below normal for early August. We get an additional push of
moisture increasing PW up to 1.5 inches along with a more unstable
environment, which will lead to greater coverage of storms.
Furthermore, the upper high will keep moving to the southwest US,
while an upper trough while an upper trough over by a Great Lakes
slowly moves east. Thus, the subtropical plume of moisture tilts
to the east advecting more moist air right over New Mexico and
bringing more chances for storms through the middle of next week.
Temperatures will be at or slightly below normal through the
middle of next week too.
Typical monsoon through the Saturday (scattered mtn storms and
isolated lowland), with isolated pockets of locally heavy rain
across the Gila. An uptick in activity is possible Sunday into early
next week as an east push brings in moisture. Temperatures remain
either at or slightly below climate normals with light to mildly
breezy winds, 5 to 15 mph, each afternoon outside of convection.
Ventilation a mix of Good to Very Good through Saturday with min RH
30 to 50% mtns and 20 to 30% lowlands.
.PRELIMINARY POINT TEMPS/POPS...
El Paso 74 92 73 93 / 20 20 20 0
Sierra Blanca 67 86 65 87 / 10 20 10 10
Las Cruces 69 91 68 92 / 20 20 20 0
Alamogordo 68 90 67 91 / 20 30 10 20
Cloudcroft 51 68 49 68 / 20 40 20 30
Truth or Consequences 68 90 68 90 / 30 30 30 10
Silver City 61 83 61 83 / 30 50 50 20
Deming 69 93 67 93 / 20 30 30 0
Lordsburg 69 91 67 91 / 20 40 40 20
West El Paso Metro 74 93 73 94 / 20 20 20 10
Dell City 67 91 67 92 / 10 10 10 10
Fort Hancock 72 94 70 95 / 20 20 10 10
Loma Linda 66 85 67 86 / 10 20 20 10
Fabens 72 93 71 93 / 10 20 20 0
Santa Teresa 72 91 69 92 / 20 20 20 0
White Sands HQ 70 90 70 91 / 20 20 20 10
Jornada Range 68 89 68 90 / 20 20 20 10
Hatch 69 91 68 91 / 20 30 30 0
Columbus 70 91 69 92 / 20 30 30 0
Orogrande 69 90 68 91 / 10 20 20 10
Mayhill 56 77 55 78 / 20 30 10 20
Mescalero 56 78 55 78 / 20 30 20 30
Timberon 54 76 53 77 / 20 30 10 20
Winston 58 82 57 82 / 30 40 40 20
Hillsboro 64 87 64 87 / 30 40 40 20
Spaceport 68 89 67 89 / 20 30 30 10
Lake Roberts 56 84 56 83 / 30 60 50 30
Hurley 62 86 62 87 / 20 40 40 20
Cliff 65 89 60 91 / 30 60 40 20
Mule Creek 61 86 62 86 / 20 70 50 30
Faywood 64 86 64 87 / 30 40 40 10
Animas 68 91 65 90 / 20 30 30 20
Hachita 68 89 65 90 / 20 30 30 10
Antelope Wells 67 90 65 90 / 30 30 30 20
Cloverdale 65 86 62 85 / 30 40 40 30
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
637 PM CDT Wed Jul 28 2021
.AVIATION...00Z TAF Package
Spotty shower activity continues over portions of the Southern
Edwards Plateau and Hill Country region but should diminish over the
next few hours as daytime heating wanes. Have kept mention of VCSH
at DRT until 02Z for the activity. VFR conditions prevail otherwise
at all sites through the TAF period. A few low clouds may develop
overnight into early Thursday morning but areal coverage should
remain limited to VFR standards. Outside of some mid-level cumulus
tomorrow afternoon, development of some isolated showers along with
perhaps a stray storm may be possible around AUS during the late
afternoon. However, confidence is currently too low at this time of
any flight impacts, to insert any mention of convection within the
TAF package. Light east-southeasterly winds trend with near calm
levels overnight along the I-35 sites.
.PREV DISCUSSION... /ISSUED 236 PM CDT Wed Jul 28 2021/
SHORT TERM (Today through Thursday)...
Latest 500mb RAP analysis places an inverted trough over
northeastern Mexico, with a notable spin on GOES 16 WV imagery.A
598dm Subtropical Ridge remains centered over north-central Kansas,
acting to suppress convection. Despite this ridging, the
aforementioned inverted trough will act to generate isolated showers
and thunderstorms this afternoon and evening, especially over the
Coastal Plains, northern Hill Country, and Southern Edwards Plateau.
An shower or storm activity should quickly wane after 03Z from east
to west, with another mild, muggy, and seasonable night in store.
Thursday looks similar to today, but we`ll be on the backside of the
inverted trough, and the Subtropical Ridge will slowly begin
migrating further south yet again. This will act to further suppress
convection, but we will still hold onto 20% PoPs as sea breeze
influences will still be at play. As far as temperatures go, it will
be slightly cooler today, as increased cloud cover in isolated
showers and storms will keep temps slightly cooler, generally in the
lower 90s north and mid to upper 90s south. Thursday will be
slightly warmer and closer to normals with highs back in the mid to
upper 90s areawide, with a few spots in the Rio Grande Plains
getting near the century mark.
LONG TERM (Thursday Night through Tuesday)...
As ridging moves back in, rain shuts off for most of the area with
the exception of some coastal sea breeze showers that may move
inland. The weekend should be a mostly dy forecast with temperatures
on the rise. Highs over the weekend to be at or just above normal.
With the humidity, the heat index values become elevated. Practice
heat safety if outdoors. By Sunday night, a cold front approaches
from the north and should remain north of the area, however, would be
the focus for some showers and thunderstorms in the afternoon
beginning on Monday. For this package, have opted to keep POPs low
until better agreement on how far south the front moves. Increased
cloudiness and some weakness in the ridge should take temperatures
down a few degrees early to mid week.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 77 96 76 95 76 / 10 20 - 20 0
Austin Bergstrom Intl Airport 76 95 75 95 75 / 10 20 - 20 0
New Braunfels Muni Airport 75 96 74 95 75 / 10 20 - 20 0
Burnet Muni Airport 75 94 75 95 75 / 10 20 - 20 0
Del Rio Intl Airport 77 99 78 99 78 / 20 - - - -
Georgetown Muni Airport 76 95 75 95 76 / 10 20 - 20 0
Hondo Muni Airport 74 95 74 95 75 / - 10 - 20 -
San Marcos Muni Airport 75 96 74 96 75 / 10 20 - 20 0
La Grange - Fayette Regional 77 96 77 95 77 / 10 20 - 30 0
San Antonio Intl Airport 75 94 76 94 76 / - 10 - 20 0
Stinson Muni Airport 77 96 77 96 77 / - 10 - 20 0
Area Forecast Discussion
National Weather Service Grand Forks ND
905 PM CDT Wed Jul 28 2021
Issued at 905 PM CDT Wed Jul 28 2021
The pesky storms finally exited Beltrami County Minnesota. The
slowly falling dew points have now worked into areas north of a
Baudette to Fargo to Valley City line. Temperatures have fallen
across far southeast ND into adjacent areas of west central MN,
but dew points there remain in the low 70s. However, dew points
there should also begin a slow fall in the next few hours.
UPDATE Issued at 627 PM CDT Wed Jul 28 2021
The front appears to have pushed through the FA now, but the high
dew points still lag well behind the wind switch. However, relief
is coming, as 50 dew points have entered the northern Red River
Valley and portions of the Devils Lake region. The last of the
early evening showers and storms are up around the Upper and Lower
Red Lakes, moving quickly southeast. So expect within the next
hour or so, the FA will be quiet again. With the drier air slowly
filtering in and decreasing winds overnight, temperatures by
morning will be a tad cooler than recently observed.
.SHORT TERM...(This afternoon through Thursday night)
Issued at 322 PM CDT Wed Jul 28 2021
Isolated severe thunderstorms are still possible this afternoon,
maybe into the early evening, though chances may be decreasing.
Cold front continues to move south and east with a prefrontal trough
still lingering over northwest and west central MN. Along/ahead of
this axis high instability is in place, but stronger CAP due to
stratus/convective debris from earlier activity today has limited
further initiation. There is some clearing in immediately ahead of the
front and may be allowing for better low level lapse rates/weakening
of the CAP, however the window is slowly closing in our CWA as the
this transitions eastward along wit the main axis of WAA/theta-E
advection in MN. High sheer with veering profiles overlap this
unstable air mass, so supercells would be possible within this
environment if a stronger updraft is able to get going. Confidence
is decreasing in initiation, but last few runs of HRRR still show
isolated cells developing immediately ahead of the front in our east
with short UH tracks for cells that do develop (we aren`t out of the
woods yet but we are getting close). Impact messaging is in line
with potential supercell development (2 inch or greater hail, winds
to 75 mph, and isolated tornado).
Rest of tonight-Thursday: Seasonable air mass returns to our CWA
with northerly flow behind the cold front and dry/stable air. Once
the flow shifts more to the north instead of northwest late
tonight/Thursday morning smoke from Canadian fires may increase into
northern MN and latest HRRR smoke model shows max surface smoke
concentrations moving into north central and northwest Mn towards
the RRV. So, while temps may be nice we may also see a return of air
.LONG TERM...(Friday through Wednesday)
Issued at 322 PM CDT Wed Jul 28 2021
Friday into Saturday...
Ridging aloft will continue to retreat south and westward throughout
the long term period. As this occurs, we will look to transition
into a northwesterly and then possibly meridional flow pattern
aloft. One outcome of this pattern shift will be a return to more
seasonable temperatures across the region for the end of the week
and continuing into next week. A ridge riding shortwave trough is
also expected to traverse the area late Friday into Saturday, and
may introduce the potential for a few showers and thunderstorms to
northwestern Minnesota. Otherwise, Saturday looks to remain quiet
and dry with widespread high temperatures in the low to mid 80s.
Sunday into next week...
As the dominant area of ridging aloft continues to weaken, it looks
like seasonable and quiet weather ahead to round out the weekend and
move into next week. While a gradual warming trend will take hold as
next week progresses, we should be able to stave off the 90s, at
least through the early week period. The next shortwave is then
progged to potentially arrive late Tuesday and bring with it the
next chance for showers and thunderstorms.
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 627 PM CDT Wed Jul 28 2021
North winds will stay gusty at KDVL/KGFK/KFAR for another hour or
so, then they should decrease again. The lower level cloud cover
should also decrease through the evening, leaving just some
higher clouds or high level smoke. North winds within the valley
(KFAR and KGFK) may get a little breezy again Thursday afternoon,
but not like today.
Area Forecast Discussion
National Weather Service Grand Rapids MI
1014 PM EDT Wed Jul 28 2021
Issued at 306 PM EDT Wed Jul 28 2021
-Damaging winds and heavy rainfall possible late tonight
-Clearing out Thursday afternoon, dry Friday
-Chance of storms Sat/sat ngt, then cool comfortable weather
Issued at 1014 PM EDT Wed Jul 28 2021
I thought it good to say something about the timing of the storms
tonight. There is an area of storms organizing over northern
Wisconsin. The storms are expected to become better organized and
move into our northwest CWA near Big Sable point near or after
midnight. The storms will continue to move south and strengthen
in response to a strengthening low level jet and mix layer capes
near 2000 to 2500 j/kg. It seems the greatest threat for damaging
winds would be south of Little Sable point and west of a line from
Big Rapids to Jackson. There does seem to be the potential for
wind gusts over 70 mph with some the bow echos expected to move
into this area early Thursday morning.
Also locally very heavy rain and localized flooding still seems to
be an issue with this storms. So of our hi-res models are showing
more than 2 inches of rain falling in less than 6 hours (really
less than 3 hours). The heaviest rain would be in the same area as
the strongest winds are possible.
.DISCUSSION...(This evening through next Wednesday)
Issued at 800 PM EDT Wed Jul 28 2021
We remain on track for potentially destructive thunderstorm wind
gusts late tonight with a heightened risk for tree and structural
damage along with a large number of power outages. The latest SPC
mesoanalysis suggests MLCAPE values of 2000-3000 J/kg even into
the 03z-05z timeframe from MKG to GRR to BTL and points westward
with little to no MLCIN. That will help allow the strongest
thunderstorm winds to mix down to the surface with little to no
Many of the last six hours or so of the HRRR runs have indicated
pockets of 90+ mph wind gusts moving into our lakeshore counties
with these storms tonight. Significant effective shear values of
50-60 kts are projected, helping aid or increase storm intensity.
Isolated tornadoes or embedded QLCS tornadoes are still on the
table as well, but the threat is likely dwarfed by the straight
line wind damage risk given the areal scope and intensity that may
be featured with these storms tonight. As for timing, we believe
that after 11pm still looks on track for our NW region, then into
the early morning hours for the majority of western, central, and
southern Lower MI.
There may also be an areal flood risk depending on possible
redevelopment of shower and thunderstorm activity behind the main
complex of storms. Some areas could get 2"-4" of rain if this
occurs, leading to some ponding of water on roads prior to
Previous Discussion below...
--Damaging winds and heavy rainfall possible late tonight--
Latest CAMs seem to have locked in on the farther north/northeast
track of the most severe convection later tonight, still hinting
at the possibility of a significant bow echo/potential derecho
impacting much or parts of wrn Lwr MI. This may be a high impact
severe weather event occurring while many folks will be sleeping,
so messaging the possibility of damaging/destructive winds well
beforehand is critical.
Timing still looks to be after 11 pm, with potential for a large
bow echo sweeping across Lk MI overnight. Also some potential for
the warm advection wing ahead of the main line becoming active a
couple hours beforehand. If that does occur, we could have some
tornado potential with discrete cells since the warm front will be
draped over the area. HRRR has 0-1km SRH of 150-200 m2/s2 with
LCLs below 1km. A QLCS-type tornado threat may also develop/exist
within the main line.
Also of note, in terms of the straight line wind potential, HRRR
still shows 70 kts at 3 km -- of potential descending rear inflow
jet into the back of that line. So some isolated pockets of
destructive 80+ mph winds seem plausible later tonight.
As far as heavy rainfall/flooding concerns, some intense rainfall
rates are likely as the strong/svr convection is coming through
tonight, although the progressive nature of the MCS may limit
the overall flooding risk. That said, some urban flooding -
possibly worthy of areal flood advisories/warnings - may also be
--Clearing out Thursday afternoon, dry Friday--
While a trailing area of rain and embedded thunder may linger on
the back side of the departing MCS Thursday morning, subsidence
and drier air arriving from the north will bring decreasing clouds
in the afternoon. Surface ridging building in on Friday brings a
pleasantly cool day with sunshine.
--Chance of storms Sat/sat ngt, then cool comfortable weather--
12Z guidance little changed in showing the next frontal boundary
dropping down from the north on Saturday with a good chance of
showers and storms in the afternoon and night. Could see briefly
warmer temps ahead of this feature on Saturday before another push
of cooler/pleasant air comes down behind it for Sunday and
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 737 PM EDT Wed Jul 28 2021
The greatest likelihood for IFR impacts at the terminals,
coincident with significant thunderstorms and associated wind
gusts potentially reaching 50 kts, is between the 05z-08z window.
This window could still shift slightly either direction as storms
are still developing as of this writing across northern WI. Kept
ceilings above 1000 ft for now but trends may necessitate bringing
a period of sub-1000 ft ceilings during this window. Additional
shower or thunderstorm development is possible beyond the greatest
severe weather threat, and that could linger toward 12z or a bit
beyond. It is tough to pin down those specifics at this time and
future amendments may be needed. A return to VFR is expected for
most locations by late Thursday morning or early afternoon.
Issued at 306 PM EDT Wed Jul 28 2021
Small Craft Advisory/Beach Hazard Statement has been issued for
late tonight through early Friday morning. While this is
primarily for the stronger north flow behind the front, it is also
intended to cover the severe wind gust threat tonight from
Also of some concern is the potential for a seiche/meteotsunami
response to a fast moving Lk MI bow echo leading to
notable/impactful water level fluctuations. However those
specifics are awfully tough to nail down until confidence in a
fast moving bow increase or become apparent. It is something that
will need watched and could require a lakeshore flood advisory or
warning at some point.
MI...Beach Hazards Statement from 2 AM EDT Thursday through Friday
morning for MIZ037-043-050-056-064-071.
LM...Small Craft Advisory from 2 AM Thursday to 8 AM EDT Friday for
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1025 PM CDT Wed Jul 28 2021
.UPDATE...917 PM CDT
Current gridded forecast is in good shape, though storms are not
moving quite as quickly at the moment. Earlier this evening rapid
thunderstorm development occurred along and ahead of several
boundaries in in northern Wisconsin, one being a warm front along
the MN/WI border and a separate boundary just to the northwest of
there. Lightning is now extensive across the entire line.
Minneapolis was in the "true" warm sector earlier this evening
extreme instability approaching 5000 J/Kg, 0-3 km shear of 37 kt
and effective shear of 47 kt. There is a deep dry layer below the
mid level moisture leading to substantial downdraft CAPE across
the region. This instability/shear space is supportive of a hybrid
bowing/supercell type environment. Therefore, damaging winds is
going to be the main concern, but with the boundaries in place and
some strong low level SRH (300-400 m2/s2 from Minneapolis to
Lacrosse, WI) along with strong instability, large hail and even a
few tornadoes are a concern in Wisconsin this evening. The Quad
Cities sounding is equally juicy, high CAPE and lower level dry
air to support storm maintenance southward in spite of some model
capping and bit less shear.
We are starting to see the signs of these storms starting to
congeal into a line of storms, and this would be the most likely
storm mode as they move southward along the instability gradient
and motion vectors southeastward. Still given the degree of shear,
some individual storm segments may continue, and thus some leading
edge QLCS tornadoes remain a concern. SPC mesoanalysis does
depict this DCAPE axis will spread southward toward the Wisconsin
border tonight and into northern Illinois. A bit lower shear and
some stronger capping into the local area still adds uncertainty
as to the southern extent of the impact, but if things get
organized the capping is not that strong and shear still
sufficient to allow this storm complex to continue into the area
tonight. Of note, 55 kt was just reported in Wausau, WI with
these storms (62 mph)
It appearing more likely that at least a portion of this complex
will make it into our area, but weather it is as potent as it is
now remains to be seen given the low level jet veering overnight
tonight and some degree of mixed layer cap forecasted. The highest
low level CAPE axis is still forecasted to increase with continued
warm air advection along the core of the MDT/ENH risk areas from
the SPC outlook, thus the mesovortex concern will continue into
southern WI, getting close to our area.
1020 PM CDT
The instability gradient now suggests that Wisconsin will be one
of the highest areas of concern, and that a slightly further
westward track to these storms may place a slightly bigger portion
of our area in the concern area later tonight. There are still
some low level stability concerns, but with the airmass still
recovering ahead of the line of storms and still getting its act
together, it is likely this complex will intensify and keep moving
for a while.
328 PM CDT
Through Thursday night...
The potential for a complex of severe thunderstorms capable of
damaging wind gusts and maybe a tornado remains the forecast focus
through tonight. Within this, substantial uncertainty remains,
enough so to limit confidence on specific impacts within the CWA.
The overall threat level remains highest within the level 3
(Enhanced) risk category per SPC Day 1 outlook given variance of
solutions and conceptually how things may play out tonight. We are
messaging a primary threat time of 12 AM to 5 AM CDT, possibly as
early as 11 PM into the far northern CWA.
Even if the main corridor of wind damage ends up to the north and
east of the CWA, the forecast southeastward trajectory of the
organized MCS potentially packing higher end wind gusts
necessitates close monitoring of southern Lake Michigan water
level monitoring for meteotsunami or seiche potential early
Thursday morning. Finally, should the MCS become more west (or
WNW) to east (or ESE) oriented, moisture and steering flow
parameters support a localized flash flooding risk, though
confidence was far too low for any Flash Flood Watch issuance.
As of mid afternoon, the primary seasonably strong short-wave and
mid-upper speed max resides on the far northeast periphery of the
impressive mid-level ridge over the central Plains. This places it
along/near the MN/Canada border. Pockets of elevated convection
downstream of this wave have extended down to central Wisconsin,
with current strongest convection north of DLH. In the immediate
near-term, despite SPC (RAP) mesoanalysis indicating 3-4k J/kg of
uncapped MLCAPE across the center of the CWA, it appears that the
extensive cirrus blow from earlier and existing convection is
limiting CI in the vicinity of remnant MCV near the MS River in
northwest Illinois. Maintained slight chance PoPs through 00z
given the very warm and oppressively humid (low-mid 70s Td) air
mass, focused into northeast Illinois and northwest Indiana. To
note, a few convective cells were developing as of this writing
over interior northern Indiana. Should a stronger thunderstorm be
able to form within the CWA, it would have a conditional downburst
Turning to the main event, later tonight-early Thursday, the lack
of widespread strong and maturing convection upstream near the
main short-wave path greatly limits predictability even at this
late hour. Two of the most utilized CAMs, the HRRR and 3km
NAMnest, for their 18z runs, have significantly divergent
solutions. Conceptually, with the very sharply northwest flow
pattern in place, storm motion to the southeast introduces the
risk for propagation into the CWA if maturation of expected MCS
occurs far enough south over Wisconsin. The forecast 850-300 mb
thickness fields and forward propagating Corfidi vectors both
point toward more south of east motion than from mean steering
flow aloft alone. This being said, the rather far north vort and
mid-level speed max path would seem to continue favor north and
east of the CWA for the highest threat for a corridor of
significant damaging winds.
Given the conflicting signals in this regard and not much help
from the available guidance, largely maintained forecast
continuity. This includes a nod toward the western flank of the
MCS orienting moreso from WNW to ESE and extending farther west
than much of the available guidance would entail, along with a
faster forward motion than much of the guidance would suggest.
Very steep mid- level lapse rates and associated extreme MUCAPE
reservoir, plus dynamical support and strong deep layer shear do
support MCS maintenance and longevity deep into the night. At
this point, think odds favor apex of a possible/likely bow echo to
pass to the north (possibly just north of far NE IL). Segment
extending back west into our CWA as per official forecast would
then have a relatively lower end but still evident damaging wind
gust threat (60-70 mph type gusts) and lesser chance for
significant (75+ mph) gusts.
Of concern for the flash flooding risk, should the west to east
orientation materialize as the complex presses southeast across
the area, forecast backward propagating Corfidi vectors slow
greatly after 06z. Thus backbuilding convection along the forward
flank of the MCS would have a flash flood risk. Observational
trends will need to be monitored closely tonight for this.
Finally, regarding the embedded QLCS tornado threat, forecast 0-3
km bulk shear magnitudes are favorable at 30+ kt. However, shear
vector orientation may tend to be more parallel to the line than
ideal so that tornado threat would be brief/shorter lived from any
transient stronger mesovortices that can develop.
There may be some lingering convection beyond 12z Thursday as the
MCS exits to the east-southeast, and as mentioned earlier, we`ll
need to monitor closely for signs of meteotsunami or seiche
development. The true cold front will not have passed yet
Thursday morning, and with the MCS expected to be primarily out of
the area, any renewed showers or storms toward mid day and into
the afternoon will be on lingering confluence ahead of this front
and on the primary MCS outflow which may be extending northwestward
through the CWA. This will eventually all be shunting southward
as one boundary into the early afternoon, and isolated to perhaps
widely scattered thunderstorms remain a threat along this, mainly
south of I-80, ending prior to sunset (possibly well before if
front clears fast enough). The high moisture and residual CAPE
would support an isolated severe threat, though confidence is low.
Heat and humidity on Thursday will maximize south of I-80 and
especially south of a PNT to RZL line, where heat indices could
approach or reach 105 degrees prior to cold frontal passage. Opted
to let the midnight shift take a look at whether a Heat Advisory
may be needed for the southern tier counties of the CWA. Cooler
and drier air will be flowing into the area driven by brisk
north-northeasterly winds through Thursday night. This will
present a rebuilding of high wave action and strong currents
after morning choppiness and seiche/meteotsunami potential. The
dangerous swimming conditions will then linger into Friday. Given
the threat for rapidly fluctuating water levels and hazardous
conditions Thursday morning and more prolonged hazardous
conditions developing Thursday PM, opted to issue a Beach Hazards
Statement from 1 AM tonight through 7 PM Friday.
328 PM CDT
Friday through Wednesday...
The extended period will start off on the cooler side with highs in
70s. Continued northeast winds, while easing, will allow for high
wave action and rip current risk to persist along Lake Michigan
beaches and dangerous swimming conditions through the afternoon.
The Great Lakes region remains under northwest flow heading into the
weekend with the strong upper jet beginning to depart to the east.
As it does so the local area will reside near the right entrance of
the jet on Saturday with a weak mid-level disturbance also moving
across the area. This will provide support for showers and a few
thunderstorms on Saturday as a cold front moves across the area.
Beyond Saturday, the extended period looks fairly quiet with surface
high pressure centered over the area and generally cooler conditions
in the 70s as the upper trough axis amplifies over the area through
For the 00Z TAFs...
Concerns through the forecast period include:
- Potential line of severe convection with strong winds during the
early morning hours and proceeding wake low winds
- NE wind shift with a cold front early Thursday afternoon
- MVFR ceilings behind the cold front Thursday afternoon
VFR conditions are expected through this evening, but focus is on
the potential impacts of imminent convection over central
Minnesota. Convection is expected quickly develop and grow upscale
into a severe MCS as it tracks southeastward through Wisconsin
this evening. Northeast Illinois will likely be located on the
southwest extent of this MCS, which is progged to reach the
Chicago metro as early as 06Z, but possibly anytime between
06-09Z. While the core of the MCS may miss the terminals to the
northeast, convective wind gusts of 35kt+ are possible along with
very heavy rain reducing visibility to IFR levels. Confidence
remains medium on convective coverage into northeast Illinois, but
some form of an outflow wind shift to the N is expected.
If the stronger convection materializes farther southwest through
the Chicago metro, SW wake flow winds gusting to 30 knots are a
possibility for a couple hours behind the convection (pre-dawn
Winds should settle W or SW for several hours while gusting
around 20 knots Thursday morning before turning NW late in the
morning and finally turning NE around noon as a cold front shifts
through the area. Behind the front, a period of MVFR ceilings are
possible through much of the afternoon before scattering by the
IL...Beach Hazards Statement...ILZ006-ILZ103-ILZ104 until 7 PM Friday.
IN...Beach Hazards Statement...INZ001-INZ002 until 7 PM Friday.
LM...Small Craft Advisory...nearshore waters
until 1 PM Friday.
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Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
848 PM EDT Wed Jul 28 2021
A cold front will approach the area tomorrow into tomorrow
night. High pressure will build in for Friday into this weekend,
bringing drier and cooler conditions. Another system may impact
the area early next week.
.NEAR TERM /THROUGH THURSDAY/...
8:45 PM UPDATE: Current radar imagery depicts widely scattered
showers and thunderstorms across northern VA and into northern
and western MD. Also notable in radar imagery has been the Bay
Breeze, which has made it well into northern VA at this time.
Storms have struggled to get going in these regions however,
owing to weak mid-level lapse rates and abundant dry air aloft.
However, the surface level dry air has allowed for some decent
wind gusts even out of relatively weak showers (up to 30 mph or
so). What this has also done is allowed for plenty of residual
outflow boundaries to be lying around. Could see those interact
with the Bay Breeze and locally enhance convection. For now,
seems like that is becoming less likely as we get further past
sunset. The 00z IAD RAOB continued to show 1000 J/kg or so of
MLCAPE, so there is still at least some instability around. RAP
mesoanalysis even shows an increase in MLCAPE through the next
several hours, albeit slight. So, can`t completely rule out a
rogue stronger storm, but for now at least, seems as though the
dry air and weak lapse rates are winning out. Per the latest RAP
mesoanalysis however, the region does lie within the left-exit
region of an approaching upper jet. So, activity may last into
the overnight hours as ascent attendant to the upper level jet
streak spreads over our area. Recent runs of the HRRR have this
type of scenario playing out, with storms lasting until after
midnight. Storms should eventually dissipate much later tonight,
giving way to partly to mostly cloudy skies late tonight. Lows
overnight will be in the upper 60s to lower 70s.
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
Tomorrow`s forecast is a challenging one locally. A very strong
MCS is expected to develop over the Upper Midwest/Lower Great
Lakes this evening into tonight. This MCS should eventually
weaken overnight as it moves into a lower CAPE environment over
the Ohio Valley. A remnant outflow boundary/convective debris
will spread over at least northern portions of the area tomorrow
morning, with a connectively enhanced speed max in the 700-500
hPa layer following immediately in its wake. There is a wide
spread of possible solutions in model guidance with respect to
subsequent development of storms across our area tomorrow. Some
solutions try to refine storms along the leading edge of the
remnant outflow as it sweeps eastward across the area. Other
solutions keep this activity suppressed. Other solutions fire
additional storms in the wake of the convective debris. Some
solutions do not.
The environment in the wake of the leftover convective debris as
the convectively enhanced speed max moves overhead is
concerning. Models such as the NAM and Euro spread a belt of
40-50 knot flow in the 700-500 hPa layer over the northern half
of our CWA by around peak heating. If we were to destabilize and
storms were to form in that type of environment, the potential
is there for a significant severe weather event, with very high
winds, large hail, and tornadoes all possible. However, there`s
considerable disagreement amongst the various models as to if
and where storms will form in the wake of what`s left of today`s
Upper Midwest system. Strong MCSs are often not handled well by
both the CAMs and global guidance, and any system that forms
today will have a strong influence on our weather for tomorrow.
As a result, confidence in the evolution of storms tomorrow
remains low. Confidence should gradually increase over time as
today`s system gets going and becomes better handled by model
guidance. We`ll continue to refine our forecast for what is a
low confidence, but also potentially high impact severe weather
A cold front will press through the area tomorrow night and
high pressure will build into the area on Friday. Much drier air
will work into the area on northerly flow behind the cold front.
Temperatures will remain warm with highs in the high 80s, but
dewpoints will drop into the 50s, making it feel a bit more
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Cooler temperatures than recent days and dry conditions with
high pressure moving overhead Saturday. High temperatures
reaching the middle 80s. The high shifts eastward to allow for a
return flow to bring in more moisture and warmth from the south
Saturday night into Sunday.
A couple of showers could develop in parts of the region Saturday
night with a chance of additional showers and a thunderstorm or two
Sunday with a cold front approaching and moving through the region.
Sunday`s highs will reach the middle to upper 80s.
A few lingering showers are possible Sunday night into Monday with a
bout of dry conditions to follow later Monday afternoon and Monday
night. Highs Monday in the middle 80s.
Tuesday appears to have some modest uncertainties as we could either
be looking at dry conditions and temperatures in the middle to upper
80s or periods of rain with embedded thunderstorms and temperatures
in the lower 80s. The first would be if high pressure hovers over us
as a weak front stays well to our northwest and a possible coastal
low pressure stays well to our southeast. The latter would be if the
coastal low wins out and moves northeast up the mid-Atlantic
seaboard. For now, we will keep an isolated shower or two for
Tuesday mainly across the southeastern half of our region.
.AVIATION /01Z THURSDAY THROUGH MONDAY/...
A few widely scattered showers and storms in the area tonight,
and will likely continue into the overnight hours. Have added
VCTS on many terminals (not CHO though). Don`t think we see much
in the way of severe weather, but could see brief restrictions
if any of these wander over the terminals. For now though, most
of the terminals remain dry.
Prevailing VFR conditions are expected through Friday.
Thunderstorms will be possible at the terminals Thursday
afternoon, potentially leading to brief restrictions. The
evolution of storms on Thursday is much more uncertain, but have
decided to at least add some VCTS to the northern terminals (so
just excluding CHO) during the afternoon. If thunderstorms were
to occur tomorrow, they could potentially be very strong, with
very high winds and hail possible. However, it`s also possible
that storms avoid the terminals. For now, wanted to add in an
inclusion of VCTS just to provide extra awareness to the
potential threat tomorrow.
Despite an isolated shower Saturday night and a few showers and a
thunderstorm possible Sunday, expect VFR conditions. Winds northwest
becoming south 5 to 10 knots Saturday into Saturday night. Winds
southwest becoming northwest around 10 knots with higher gusts
Sub-SCA conditions are expected in light northerly flow today.
Winds will turn southerly tomorrow and may approach SCA levels
briefly in southerly channeling tomorrow afternoon. However,
confidence in that occurring was too low to issue an SCA at the
moment. SMWs will be possible in association with any thunderstorms
that move over the waters both this afternoon and tomorrow
afternoon. The winds in any thunderstorms tomorrow afternoon
could be very strong, with over 50 knots possible in the
strongest cells. Additionally, in the wake of that frontal
boundary, winds are expected to exceed SCA criteria, so have
added an SCA starting late tomorrow night, which will continue
through at least Friday morning.
No marine hazards expected Saturday through Sunday night. Winds
northwest becoming south around 10 knots Saturday and Saturday
night. Winds generally southwest shifting late to northwest at 10 to
15 knots Sunday and Sunday night.
Southerly flow ahead of an approaching cold front will likely
bring tides up to action stage over the next couple days. Minor
flooding may be possible at the most sensitive sites like
Annapolis. Northwest flow behind the front by Friday should
allow anomalies to drop.
MARINE...Small Craft Advisory from 10 PM Thursday to 6 AM EDT Friday
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
656 PM CDT Wed Jul 28 2021
.UPDATED for 00Z Aviation Discussion...
Issued at 646 PM CDT Wed Jul 28 2021
.SHORT TERM...(This evening through Thursday night)
Issued at 343 PM CDT Wed Jul 28 2021
Surface analysis this afternoon shows a surface low over the ND/MN
border with is warm front snaking SE through central MN into northern
IA and its cold front sagging SW through the Dakotas. High pressure
sits to the NW of this system. Aloft, a trough resides over the
eastern CONUS with a large ridge over the western CONUS. While WNW-
ESE is placed over the Upper Midwest, several embedded shortwaves are
immersed within the flow, and are expected to jet across the region
through the rest of this afternoon and evening.
Clouds have dispersed efficiently this afternoon across central-
southern MN well after this morning`s convection. Combined with
southerly winds, this has allowed temperatures in western MN to soar
into the 90s with much of the area having a surge in moisture,
pushing dewpoints into the 70s. While this certainly has contributed
to high heat index values over 100 (and near 110 in some areas), this
is also allowing instability to surge across the area. SPC
mesoanalysis pages indicate MUCAPE values as high as 4000-5000 j/kg
over western and southern MN, but there is still a relative minima of
1000-2000 j/kg over western WI, which is eventually where storm
development is expected. The surface low is expected to drive ESE
across southern MN (atop the TC metro) and into central WI by
midnight, with high pressure then filling into MN/WI overnight
through Thursday. CAMs, which differing in exact placement, are still
indicating a good degree of confidence in t-storm development over
northern MN and growing into an organized complex that will push SE
through east-central MN and west-central WI then into southern WI
late this afternoon through this evening. The trickiest part is how
far west the storms may develop as the HRRR still confines the storm
development into WI while other CAMs have nudged the convection a bit
further west into MN. Still, there is little to stray from the idea
of having a powerful bowing complex for western and southern WI this
evening which may well contain damaging winds and large hail. Later
mesoscale discussions from SPC will capture more detailed elements so
keep up with the latest discussions on their end to see how this
potential severe weather event will develop.
Once the storms exit the area and the cold front pushes through, a
noticeably calmer/cooler/drier environment will settle upon the WFO
MPX coverage area for tomorrow. This will drop highs from the 90-100
degree range today to the 80-85 degree range tomorrow. More notably,
dewpoints will drop from the low-mid 70s to the 50s, making for much
less humid conditions.
The only other issue to deal with in the short term will be the
return of wildfire smoke to the area. HRRR Smoke modeling plus
collab from the MPCA indicates that air quality will suffer with
subsidence forcing smoke aloft down near the surface. As such, have
added smoke mention to the gridded/text products along with the Air
Quality Alert issued by the MPCA.
.LONG TERM...(Friday through Wednesday)
Issued at 343 PM CDT Wed Jul 28 2021
Much more tranquil conditions are expected across the region from
the end of this week into the middle portion of next week. Weak
isentropic lift in advance of a frontal system developing over the
central Plains Friday into Saturday may result in isolated to
scattered showers and thunderstorms over far southwestern portions of
the area. Additional isolated showers and thunderstorms may be
possible Saturday in western Wisconsin as a secondary cold front
drops through the area. While this front will not be much in terms of
generating precipitation, it will be a reinforcing shot of cooler
and drier air across the region for early next week. From Sunday
onward, a dry forecast is in place. In addition, temperatures will
again take a bit of a hit, with highs falling back to the upper 70s
to lower 80s along with lows falling into the 50s to lower 60s.
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 646 PM CDT Wed Jul 28 2021
Scattered showers are possible at the Minnesota TAF sites, and
strong thunderstorms are possible in the Wisconsin TAF sites this
evening. The precipitation should exit the region overnight, with VFR
conditions and northwest winds expected for Thursday.
The higher chances for thunder should be east of KMSP, so have VFR
showers in the TAFS. There is still a chance KMSP could see a storm,
but did not include mention in the TAFS. Precipitation chances should
end by midnight, and then expect VFR conditions with
/OUTLOOK FOR KMSP/
Fri...VFR. Winds SE 5-10 kts becoming SW.
Sat...VFR. Winds NW 10-20 kts.
Sun...VFR. Winds N 10 kts.
MN...Excessive Heat Warning until 9 PM CDT this evening for Anoka-Benton-
Kandiyohi-Lac Qui Parle-Le Sueur-Martin-McLeod-Meeker-Nicollet-
Heat Advisory until 9 PM CDT this evening for Douglas-Freeborn-
Area Forecast Discussion
National Weather Service Phoenix AZ
513 PM MST Wed Jul 28 2021
Updated Aviation discussion.
One more day of warmer and minimal storm chances today before rain
chances increase late in the week. Another weather disturbance
expected to affect the region bringing a return to more widespread
shower and thunderstorm activity starting Thursday afternoon,
likely persisting into the weekend. Drier conditions should then
prevail by early next week.
Monsoon activity across the region has returned to a more typical
pattern this afternoon with storms mainly developing over SW AZ and
SE CA as a weak inverted trof moves across that region. This is the
same inverted trof/jet max that brought TS activity to SE AZ and
areas of strong winds/blowing dust to parts of South-Central AZ
yesterday afternoon/evening. Latest WV satellite imagery is showing
somewhat drier air filtering into eastern/central AZ, which is
expected to greatly limit TS activity over that region this
afternoon/evening. The 12Z HREF agrees with the lower potential
compared to yesterday, showing isolated to scattered storms this
afternoon along the Mogollon Rim and over extreme southeast
Arizona through this evening.
The semi quiet monsoon period will quickly come to an end on
Thursday as a well defined, but weakening upper level low center
currently moving westward through southern Texas/northern Mexico
moves into the region. During the day Thursday, broad upper level
ascent will spread westward across much of Arizona as the trough
enters the region. Moisture levels and instability will be
sufficient for scattered to possibly widespread storms developing
across the eastern Arizona high terrain Thursday afternoon with
strong winds, heavy rainfall, and localized flooding all possible.
Latest (12Z) SPC HREF guidance is showing 50-70% chance of wind
gusts aoa 35 kts across south-central AZ/SW AZ during the
afternoon/evening hours on Thursday as it show an rather organized
area of convection marching westward into the lower deserts, with
even a 10+% chance of wind gusts aoa 50 kts. ALthough fairly rapid
storm motion will limit rainfall totals somewhat, the strong/severe
nature of these storms will still likely allow them to produce
localized flooding, especially over the burn scar areas. Latest HRRR
and HREF guidance is showing this complex of showers/TS progressing
westward to about the Colorado River Valley during the late evening
hours on Thursday/into early morning, but instability will be much
more limited farther west. As is typical during these overnight
hours. the main impact of these storms further west will be
localized flash flooding, with wind and dust being a lesser threat.
Given the heavy rainfall threat across the region, WPC has upgraded
their ERO to "slight" for eastern AZ (including southern Gila
County) on its day 2 outlook and much of western AZ (including LA
Paz and parts of Yuma County on its day 3 outlook.
The inverted trough is forecast to exit the region to the northwest
Friday morning, but not before spreading modest moisture throughout
our area. Storm chances for Friday still look to be a bit more
uncertain with the quicker progression of the inverted trough and
the possibility of storm suppression due to large areas being worked
over by Thursday`s activity. Sufficient moisture will still be in
place in most areas Friday, but some drying is now forecast across
eastern Arizona. Shower and storm chances for Friday afternoon and
evening are now more favored from Phoenix westward with the help of
broad ascent associated with a south to north oriented upper level
jet over California. Should also have some isolated to scattered
storms across the eastern Arizona high terrain, but the drying
coming out of New Mexico should limit coverage. Storm chances
Saturday look to shift back to the east with another jet streak
coming up from the south providing ascent more focused across
central and eastern Arizona while better moisture is again seen
across eastern Arizona. Near to slightly above normal monsoon
moisture levels and forecast soundings for Friday and Saturday point
toward a mix of storm threats from strong winds to locally heavy
rainfall and possible flooding.
Drier air will begin working in from the southwest starting
Sunday, likely ending storm chances across most of the western
deserts and considerably lowering chances elsewhere. The
southwesterly drying flow will result from the subtropical high
weakening while shifting south and an upper level trough becoming
the dominant feature along the West Coast. This unfavorable
monsoon flow pattern should persist through early next week with
another high center forming to our southwest on Monday and even
drier northwesterly flow spreading through the region. Minimal
storm chances over the eastern Arizona high terrain are expected
for Monday and Tuesday, but for now it seems the lower deserts
will be dry for a few days. Eventually, model ensembles show the
new high center shifting northeastward into the Four Corners area
later next week which will likely bring a return to more favorable
monsoon moisture flow out of the southeast and increasing storm
Temperatures today and Thursday should be the warmest of the week
with highs across the western deserts between 109-112 degrees to
102-105 degrees in the Phoenix area. Cooling will occur by Friday
and last through the weekend with forecast highs from the upper
90s in the Phoenix area to 100-105 degrees over the western
deserts. Temperatures should return to near normal readings for
the western deserts during the first half of next week, while the
south-central Arizona deserts will likely fall just short of
.AVIATION...Updated at 0020Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Thunderstorm chances on the Valley floor remain below 10% through
mid afternoon Thursday. Surface winds are expected to favor
westerly directions this evening. However, that may last only
until 04Z or so before more variable directions develop (but with
speeds remaining below 10kts). Typical light nocturnal winds are
anticipated to develop by 07Z or so (earlier for KSDL and KDVT and
later for KPHX). Late tonight and during the morning Thursday,
thick high clouds are anticipated. There are some indications of
embedded sprinkles. Not enough to go on at this time to insert
VCSH or have any noteworthy ceiling altitudes.
Thursday afternoon and evening is anticipated to be quite a bit
more active with more storms over the higher terrain north and
east of the Phoenix area as well as southeast Arizona. This will
lead to a significantly higher potential for impactful outflows
and storms on the Valley floor (35-45% chance). Uncertainties
remain in terms of storm coverage as well as timing and strength
Southeast California/Southwest Arizona including KIPL and KBLH:
Thunderstorm chances at the TAF sites remain below 10% through
mid afternoon Thursday before increasing to 15-25% Thursday
evening. Apart from thunderstorms, winds are anticipated to remain
light and favor south and southeast directions. High clouds will
increase considerably late tonight and hang around for much of the
Saturday through Wednesday:
Unsettled conditions are likely through the weekend with a couple
of weather disturbances moving through the region. This should
bring daily shower and storm chances across the entire area on
Saturday before decreasing chances from west to east Sunday
through next Wednesday. Main threats will be strong thunderstorm
winds, heavy rainfall and localized flooding. Temperatures will
range from near to slightly below normals the bulk of the period.
Minimum afternoon humidity values will range from 25-45% through
the weekend before falling back to 15-30% early next week.
Overnight recovery will be mostly good to excellent in a 40-80%
range. Apart from thunderstorms, winds will favor typical daily
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
Area Forecast Discussion
National Weather Service Riverton WY
455 PM MDT Wed Jul 28 2021
.SHORT TERM...(This evening through Thursday night)
Issued at 309 PM MDT Wed Jul 28 2021
Complicated weather pattern today has brought a host of different
weather to western and central Wyoming. First, a cool front moved
south out of Montana overnight into the morning hours east of the
divide. Yes, it is cooler than yesterday, but it`s still quite
warm and feels warmer because overnight temperatures did not cool
off as normal. Also, the northerly flow has brought increased
smoke into the basins, reducing visibilities and decreasing air
quality. Thus, an the Air Quality Alert has been extended through
at least tomorrow. Second, monsoon moisture along with increased
instability and buoyancy have brought scattered showers and
thunderstorms to much of western Wyoming. Storm motions are very
slow and precipitable water amounts are very high, around 150
percent. Thus, the likelihood of flooding has increased this
afternoon and evening due to precipitation rates on the order of 1
inch in 30 to 45 minutes. High resolution models continue to show
more organized areas of moderate precipitation develop across
western WY late this afternoon into the evening hours. Isolated
storms are possible early in the evening along the eastern
foothills of the Wind Rivers and southern Absarokas, which then
move northeastward. The HRRR continues to show some storms
developing around midnight from Buffalo SW toward Shoshoni. So,
expected isolated showers and very isolated thunderstorms after
The shortwave trough rotating around the high seems to hang along
a boundary across northern WY to bring precipitation to north-
central WY Thursday morning. Otherwise, Thursday morning will be
mostly to partly cloudy across the area with another possibility
of above normal minimum temps. Thursday will be similar to today
as slow moving storms develop, mainly over the mountain areas,
with a very high chance of heavy rainfall rates which could again
lead to flooding. Some of the storms over Natrona county could be
strong too, with SPC highlighting the area for a marginal risk of
severe storms. The focus Thursday late afternoon and evening will
be from the west-central mountains northeastward to the Bighorns,
though everywhere across the area will have a chance of storms and
precipitation. The shortwave trough riding around the high
Thursday evening should bring moderate precipitation to a large
area from the eastern Wind Rivers NNE across the Bighorns and
Johnson County. Thursday night should be a focus for the east side
of the Bighorns for heavy precipitation, according to the NAM,
GFS, and HREF. Afternoon high temperatures should decrease another
5-8 degrees Thursday over Wednesday, and humidities will increase
as well, especially in areas of precipitation. There is a
possibility of fog in the western valleys Thursday morning as
recent precipitation will add to low level moisture. Generally
wind flow the next couple of days will be northwest across western
WY, and north to northeast east of the divide into Sweetwater
.LONG TERM...(Friday through Wednesday)
Issued at 309 PM MDT Wed Jul 28 2021
Monsoonal moisture continues to push into the region Friday and
Saturday, as a surface high sits to the southeast and meridional flow
aloft over the western CONUS helps usher higher PW air northward.
Despite continued cooling of temperatures (lower highs generally in
the 80s), there should be enough instability for continued
widespread showers and thunderstorms. Given the amplified large-
scale ridge over the region, storm-motion will be quite slow. This
leads to continued localized flooding concerns, especially over
steep terrain where rainfall can be funneled.
Saturday night into Sunday, a broad surface high slides down the
Plains from Canada. The pressure gradient around this high is
forecast to push drier and slightly cooler air westward. Locations
east of the Divide should see less shower activity during the
afternoon. Far western and southwestern Wyoming will still have a
solid moisture connection in the monsoonal flow, so scattered storms
continue to be possible there.
The EC and GFS disagree on how to bring a well-defined shortwave
through the ridge early next week. The GFS is more progressive and
brings additional lift into central Wyoming Monday, which would
translate into additional chances for daytime showers and
thunderstorms. Despite the differences, both models keep early week
temperatures about 5 degrees below average due to increased cloud
cover and a relatively moist air mass.
.AVIATION...(For the 00Z TAFS through 00Z Friday)
Issued at 445 PM MDT Wed Jul 28 2021
Scattered showers and thunderstorms will occur in the west and
central through 06Z. Only isolated activity will occur elsewhere.
Surface winds will generally be light; however, in the vicinity of
thunderstorms, brief erratic wind gusts of 30 to 40 kt are possible.
Showers will persist into the early morning hours Thursday.
Thursday begins with abundant high cloud cover, and by the
afternoon, additional showers and thunderstorms are forecast to
develop. Lightning, brief heavy rain, and gusty winds will be the
main threats, but small hail cannot be ruled out.
Issued AT 200 PM MDT Wed Jul 28 2021
Hot and dry is quickly turning to warm and wet today and the rest
of the week. Scattered showers and thunderstorms across western WY
will continue into the evening with heavy rainfall a good
possibility. Isolated showers and storms will then continue
overnight and possibly move eastward into central and northern WY.
Gusty north winds east of the divide will continue into the
evening hours as well. Thursday will continue with isolated
showers in the morning transitioning to scattered showers and
thunderstorms in the afternoon and evening. Again, heavy rainfall
will be the biggest threat and hopefully lightning will strike in
wet areas. Thursday evening could be quite wet across portions of
north-central WY. Friday and Saturday will see continued cooling
temperatures as well as good chances of precipitation across much