Special Weather Statement, NWS Twin Cities, MN

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
145 AM CDT Wed Jul 26 2023

.UPDATE...
Issued at 135 AM CDT Wed Jul 26 2023

Updated to include 06z aviation discussion below.

&&

.DISCUSSION...(This evening through Tuesday)
Issued at 226 PM CDT Tue Jul 25 2023

KEY MESSAGES:

- Severe MCS possible along the MN River Valley this evening.

- Dangerous heat Wednesday through Thursday, with afternoon heat
  indices around 100, with lows Thursday morning remaining in the
  70s.

- Scattered Thunderstorms possible Thursday afternoon and evening, a
  few may be severe.

- Temperatures cool back down closer to normal this weekend into
  next week.

Water vapor imagery this afternoon shows a shortwave cresting the
ridge over central ND. MUCAPE ahead of this shortwave is on the
order of 4000-6000 j/kg per SPC mesoanalysis, which will allow for
the development of strong convection shortly. CAMs are a bit all over
the place on how storms evolve overnight, but the general idea is
that storms that develop over the Dakotas this afternoon will travel
southeast along the CAPE gradient. Said CAPE gradient currently
angles SSE from south central ND toward Des Moines and is expected to
only nudge northeast a little tonight, which means the favored
corridor for a forward propagating MCS would be from west central MN
toward north central Iowa. The current Day 1 SPC convective outlook
covers this well and from the CAMs perspective, the HopWRF members
show a similar progression of things. This means the highest PoPs
tonight are south of I-94, with the Twin Cities possibly sitting in a
position where we see another rain event go "ope, lemme just sneak
past ya."

The main story for Wednesday and Thursday continues to be the heat.
For Wednesday, it is looking like activity tonight moves through our
area fast enough as to where it will have little impact on
temperatures on Wednesday (at least in MN). Therefore, we boosted
highs toward the 75th percentile of the NBM. Dewpoint temperatures
look to mix out into the mid 60s, which will hold heat index values
around 100, but full sun and light winds will allow Wet-bulb Globe
Temperatures (WBGT) to top out in the 86-88 range (getting into the
Extreme level for our region) from the MN River Valley up into the
Twin Cities. Overnight lows Wed night into Thursday morning will stay
in the 70s, with similar hot conditions expected on Thursday
afternoon. Therefore, we issued a Heat Advisory for Wednesday
through Thursday where the most extreme WBGT values overlap both
days, with limited cooling off Wednesday night. A further expansion
of this Advisory to the west is possible for Wednesday and to the
south and east on Thursday, but we have time to figure out any
possible expansions and upgrades to an Excessive Heat Warning in the
Twin Cities for Thursday.

As for precipitation chances, building heights will shut down precip
generation over us Wed/Wed night. Thursday, a weak cold front will
sag into the MPX area and will encounter a very unstable airmass
(likely 3000+ j/kg of mlCAPE). However, it's still uncertain where
enough forcing will exist to force convection through a capping
inversion associated with the EML. If storms develop, they will be in
a more than favorable environment for severe weather (wind/hail) and
the current Marginal Risk in the SPC Day 3 convective outlook covers
this threat well, though an upgrade to a Slight in the future seems
likely once there's a bit more confidence in where we'll see
convection develop Thursday afternoon.

Friday through Tuesday... Models have sped up the fronts progression
to the south, where by Friday, we're now expecting highs to largely
remain in the 80s and they will remain there through the first half
of next week. Though the surface front will be south of us on Friday,
the elevated thermal gradient will be over southern MN, so additional
elevated thunderstorm development looks possible Friday afternoon.
Eventually, the northerly winds will push the frontal boundary far
enough south to where our precipitation chances are now looking
pretty minimal for the weekend. However, next week, the northern
stream looks to reside over the northern tier states, with the
weekend ridge flattening out and a zonal flow taking over. This
brings about the chances for more storms next week with any passing
shortwaves we may see. However, this far out, there's little
agreement on timing/strength of any of these waves, which means you
see the return of fairly common slight chance/low chance PoPs to the
forecast for early next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 135 AM CDT Wed Jul 26 2023

Still dealing with the MCS moving ESE over east-central MN which has
mainly impacted MSP with 35-45kt gusts but also glancing around the
remaining terminals over the next couple hours. Brief MVFR conditions
possible under the heavy downpours should they occur. Otherwise,
conditions will gradually improve through the remainder of the
overnight hours into tomorrow. Winds will settle on W to NW through
tomorrow then become light/variable Wednesday night into Thursday
morning.

KMSP...Main complex of storms has pushed through MSP, producing a
36kt wind gust. Conditions will improve behind the complex, though
some additional storms are possible in w-central MN tracking ESE. The
overall storm threat will end prior to daybreak with VFR conditions
expected to prevail thereafter.

/OUTLOOK FOR KMSP/
Thu...VFR. Chc evening TSRA. Wind SW 5-15 kts.
Fri...VFR. Chc TSRA. Wind NE 5 kts.
Sat...VFR. Wind NE 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Heat Advisory from 10 AM this morning to 8 PM CDT Thursday for
     Anoka-Blue Earth-Brown-Carver-Chisago-Dakota-Hennepin-Isanti-
     Le Sueur-McLeod-Meeker-Nicollet-Ramsey-Redwood-Renville-Scott-
     Sherburne-Sibley-Washington-Wright.

WI...Heat Advisory from 10 AM this morning to 8 PM CDT Thursday for
     Pierce-St. Croix.

&&

UPDATE...JPC
DISCUSSION...MPG
AVIATION...JPC

Hazardous Weather Outlook
National Weather Service Twin Cities/Chanhassen MN
409 PM CDT Tue Jul 25 2023

MNZ041-042-047>049-054>060-064>070-073>078-082>085-091>093-262115-
Douglas-Todd-Stevens-Pope-Stearns-Lac Qui Parle-Swift-Chippewa-
Kandiyohi-Meeker-Wright-Hennepin-Yellow Medicine-Renville-McLeod-
Sibley-Carver-Scott-Dakota-Redwood-Brown-Nicollet-Le Sueur-Rice-
Goodhue-Watonwan-Blue Earth-Waseca-Steele-Martin-Faribault-
Freeborn-
409 PM CDT Tue Jul 25 2023

This Hazardous Weather Outlook is for portions of central
Minnesota...east central Minnesota...south central Minnesota...
southeast Minnesota...southwest Minnesota and west central
Minnesota.

.DAY ONE...Tonight.

Another round of scattered thunderstorms is expected to move
across the region late this evening and overnight. Wind and hail
are the primary threats with these thunderstorms, with the
greatest risk of severe weather extending from west central into
south central Minnesota.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Hot and humid conditions are expected Wednesday and Thursday.
Excessive heat is likely with temperatures in the middle and
upper 90s and maximum heat indices from the mid 90s to low 100s.

A few rounds of thunderstorms are also possible, with a marginal
risk of severe weather across the region late Thursday and
Thursday night.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation will not be needed.

MNZ043>045-050>053-061>063-WIZ014>016-023>028-262115-
Morrison-Mille Lacs-Kanabec-Benton-Sherburne-Isanti-Chisago-Anoka-
Ramsey-Washington-Polk-Barron-Rusk-St. Croix-Pierce-Dunn-Pepin-
Chippewa-Eau Claire-
409 PM CDT Tue Jul 25 2023

This Hazardous Weather Outlook is for portions of central
Minnesota...east central Minnesota...northwest Wisconsin and west
central Wisconsin.

.DAY ONE...Tonight.

No hazardous weather expected at this time.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Hot and humid conditions are expected Wednesday and Thursday.
Excessive heat is likely with temperatures in the middle and
upper 90s and maximum heat indices from the mid 90s to low 100s.

A few rounds of thunderstorms are also possible, with a marginal
risk of severe weather across the region late Thursday and
Thursday night.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation will not be needed.

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