Special Weather Statement, NWS Twin Cities, MN

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
414 AM CDT Wed Aug 12 2020

.SHORT TERM...(Today through Thursday)
Issued at 414 AM CDT Wed Aug 12 2020

A sub-severe MCS is marching eastward across northern South Dakota
early this morning. It is being driven by strong moisture
advection at 925 mb and a fair amount of elevated instability.
Global models have not handled this feature well at all, while
some of the CAMs have picked up on it and continues to bring it
eastward into central Minnesota later this morning. There is an
impressive north-south moisture gradient across western MN early
this morning with pwats greater than 1.5 inches west and less than
0.8 inches east. So far convection has not shown any signs of
decaying, but it hasn't yet outrun the instability and deep
moisture environment. Given its eastward motion around 40 mph,
it's possible it will begin to do that during the next several
hours unless the moisture axis begins to build eastward a bit
quicker than current trends. The feature has a pretty impressive
MCV as well, which could also help maintain its intensity well
into the morning hours. One would expect it to track more
southeast along the NW-SE instability gradient with time, but it
has shown no signs of doing that yet either. I do expect some
increase in convective activity a little farther south by
sunrise, but the main circulation should continue almost due east
across central MN into the early afternoon. Increased PoPs to
greater than 80 percent across west central MN, then slowly
decrease them to high chance by the time it would reach east
central and/or south central MN mid to late morning given the
increasing uncertainty. The remnant circulation may spark
additional convection during the afternoon across eastern and
southern MN, so maintained low PoPs through that time. The
eastward progression of the moisture plume will halt as it reaches
WI this afternoon, so kept PoPs quite low there. Temperatures may
be suppressed from morning convection/outflows and extensive
cloudiness for much of the day, so kept highs on the cooler side
of guidance, particularly of those members that haven't resolved
this feature.

Fairly steep lapse rates of 7-8C/km and pwats of about an inch and
a half will maintain decent instability through tonight across
western MN. Shear is almost non-existent, but a LLJ of 35 kts
could produce a few isolated thunderstorms, especially late. These
chances will continue Thursday, but an interesting feature to keep
an eye on could be approaching southern MN by late afternoon.
An MCS over western Kansas early this morning has been resolved
well by all of the global guidance. The remnant short wave will
slowly advance east northeast across the Plains and mid Missouri
Valley today into Thursday, reaching southern and eastern MN
Thursday evening. If this continues to be advertised, PoPs may
need to be raised late Thursday afternoon and especially Thursday
night across parts of the area.

.LONG TERM...(Thursday night through Tuesday)
Issued at 414 AM CDT Wed Aug 12 2020

The highlights of the long term are the chances for showers and
thunderstorms on Friday and Saturday, followed by cooler, drier
weather Sunday through the end of the period.

Thursday night the deterministic models are in agreement that an
upper trough will be located somewhere around southwest Minnesota.
The Canadian has PWATs around 2 inches and is stronger and faster
with this feature resulting in very heavy rainfall from southwest
Minnesota through the Twin Cities and then weakening as it moves
off into west central Wisconsin. The GFS is a little farther west
and several hours slower while the ECMWF keeps the heaviest
precipitation near and south of the Iowa border. Friday evening
another shortwave will traverse the area while a surface low in
Canada will drag a cold front through the CWA sometime in the
overnight hours. This will result in another chance for showers
and thunderstorms. Dewpoints in the upper 60s to low 70s and mid-
level lapse rates approaching 8 C/km are forecast to yield MLCAPE
values in the 2000-3000 J/kg range over west central Minnesota,
central Minnesota and southern Minnesota giving these areas the
best chance for strong to severe thunderstorms. The SPC has placed
much of Minnesota under a Slight Risk during this period, while
the WPC also has the same area under a Marginal Risk for excessive
rainfall. The instability lessens quickly from far eastern
Minnesota into west central Wisconsin so the these areas are under
a Marginal Risk for severe storms.

After the front passes things will start to cool off and dry out,
although some light showers could linger behind the front through
the day on Saturday. High pressure will build into the area behind
the front and set us up for several very nice days for this time of
the year. Northwest flow will keep high temperatures in the 70s with
dewpoints in the 50s through the period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1209 AM CDT Wed Aug 12 2020

VFR conditions overnight, but confidence is increasing in  some
showers and thunderstorms Wednesday morning across the western TAF
sites. This are of precipitation is currently an area of
thunderstorms across the eastern Dakotas, but it should weaken as
it moves eastward during the day, but it could bring some thunder
and MVFR conditions at times. Winds will be out of the southeast.

KMSP...
VFR conditions this evening and overnight, but could have some
showers move in around late morning on Wednesday. Winds will be
out of the southeast.

/OUTLOOK FOR KMSP/
Thu...Mainly VFR. Chance MVFR/TSRA. Wind SE 10-15 kts.
Fri...Mainly VFR. Chance MVFR/TSRA. Wind SE 10-15 kts.
Sat...VFR with MVFR/TSRA possible late. Wind NW at 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&

SHORT TERM...Borghoff
LONG TERM...CEO
AVIATION...JRB

Hazardous Weather Outlook
National Weather Service Twin Cities/Chanhassen MN
437 AM CDT Wed Aug 12 2020

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
130945-
Douglas-Todd-Morrison-Mille Lacs-Kanabec-Stevens-Pope-Stearns-
Benton-Sherburne-Isanti-Chisago-Lac Qui Parle-Swift-Chippewa-
Kandiyohi-Meeker-Wright-Hennepin-Anoka-Ramsey-Washington-
Yellow Medicine-Renville-McLeod-Sibley-Carver-Scott-Dakota-
Redwood-Brown-Nicollet-Le Sueur-Rice-Goodhue-Watonwan-Blue Earth-
Waseca-Steele-Martin-Faribault-Freeborn-Polk-Barron-Rusk-
St. Croix-Pierce-Dunn-Pepin-Eau Claire-
437 AM CDT Wed Aug 12 2020

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

.DAY ONE...Today and Tonight.

There is a chance of thunderstorms through tonight. Widespread
severe weather is not expected, but a couple thunderstorms could
be severe with large hail and damaging winds.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Periodic thunderstorms are expected Thursday through Saturday.
There is a Marginal Risk for severe thunderstorms across western
Minnesota Thursday and a Slight Risk across most of Minnesota on
Friday. Large hail and damaging winds are possible, along with
locally heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation may be needed.

Borghoff

Special Weather Statement
National Weather Service Twin Cities/Chanhassen MN
521 AM CDT Wed Aug 12 2020

MNZ054-055-121100-
Lac Qui Parle-Swift-
521 AM CDT Wed Aug 12 2020

...A LINE OF STORMS WILL AFFECT LAC QUI PARLE AND WESTERN SWIFT
COUNTIES...

At 521 AM CDT, radar indicated strong thunderstorms were located
along a line extending from near Lagoona Beach to 8 miles southeast
of Milbank to Tunerville. Movement was east at 45 mph.

Winds in excess of 30 mph are possible with these storms.

These storms will be near...
  Bellingham around 535 AM CDT.
  Marietta around 540 AM CDT.
  Lake Oliver around 545 AM CDT.
  Madison and Appleton around 555 AM CDT.

Other locations impacted by these storms include Louisburg, Nassau,
Big Stone National Wildlife Refuge, Madison Airport, Florida Creek
Wildlife Management Area and Appleton Airport.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 4526 9645 4525 9629 4522 9627 4519 9617
      4519 9612 4518 9610 4524 9610 4524 9612
      4541 9612 4541 9592 4505 9608 4480 9623
      4480 9645
TIME...MOT...LOC 1021Z 268DEG 38KT 4539 9641 4517 9648 4489 9666

Borghoff

Special Weather Statement
National Weather Service Twin Cities/Chanhassen MN
555 AM CDT Wed Aug 12 2020

MNZ041-047-048-121130-
Stevens-Pope-Douglas-
555 AM CDT Wed Aug 12 2020

...A LINE OF STORMS WILL AFFECT WESTERN DOUGLAS...WESTERN POPE AND
STEVENS COUNTIES...

At 555 AM CDT, radar indicated strong thunderstorms were located
along a line extending from Wendell to near Artichoke. Movement was
northeast at 35 mph.

Winds in excess of 30 mph and dime size hail are possible with these
storms.

These storms will be near...
  Morris and Hancock around 620 AM CDT.
  Cyrus around 630 AM CDT.

Other locations impacted by these storms include Lake Emily, Alberta,
Garfield, Melby, Fish Lake, Holmes City, Farwell, Millerville and
Morris Airport.

LAT...LON 4576 9615 4576 9577 4610 9577 4611 9547
      4542 9547 4541 9615
TIME...MOT...LOC 1055Z 238DEG 31KT 4604 9607 4542 9607

Borghoff