Special Weather Statement, NWS Twin Cities, MN

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1058 PM CDT Thu Aug 13 2020

.SHORT TERM...(This evening through Saturday)
Issued at 310 PM CDT Thu Aug 13 2020

...Enhanced Risk for Severe Weather Friday through Friday Evening
with Large Hail, Damaging Winds and Isolated Tornadoes Possible...

A warm front has lifted north through most of the WFO MPX coverage
area today, associated with a low pressure center sitting over far
northeastern ND with its trailing cold front snaking west
southwest over eastern ND, central SD into central WY. Aloft, A
well-defined upper level trough over western Canada will shift
eastward, dropping into the Dakotas overnight tonight.

Dewpoints have surged into the lower-mid 70s area-wide, which
combined with highs hitting the mid 80s to lower 90s, has pushed
heat index values into the mid-upper 90s for much of the MN
portion of the coverage area and lower 90s in western WI. However,
the bigger point here is that a highly moist atmosphere is in
place as a deep plume of moisture from the deep South and
associated with the western cold front pushes PWATs to around
1.5". Little change in such atmosphere is expected through
tomorrow afternoon, even with an increase in cloud cover,
therefore making for a highly unstable atmosphere ahead of the
approaching cold front. A few stray showers/thunderstorms are
possible during the overnight hours in far western MN into north-
central portions of the coverage area close to daybreak, and this
activity may well be part of diminishing severe weather over
northwestern MN overnight. So, while the thunderstorms may be in a
weakened fashion by the time they arrive in central MN, they
will deposit residual boundaries across our coverage area which
will act as foci for thunderstorm development later during the day
on Friday.

The low pressure center will develop further but generally remain
in place tonight into tomorrow, but as the upper trough makes its
way into northern MN by late Friday morning, this will give
impetus for the cold front to push to the Dakota/MN border by
midday Friday, continuing east during the day and move into
northern WI Friday evening then out of MN and into eastern-
southern WI by Saturday morning. Ahead of this front, strong
southerly winds to the tune of a 40-50kt LLJ combined with
collapsing H5 heights will help enhance thunderstorm development
with little in the way to mitigate as such (i.e. no effective
capping mechanism). In addition, the height falls will aid in
steepening lapse rates, sufficient for hail development with
multiple storms. The overall scenario here: thunderstorms are
expected to develop in western MN by early afternoon and steadily
progress eastward through the rest of the day and into the
evening. Storms will take on a more discrete fashion at first, a
more supercellular nature close to the low pressure center triple-
point, then increase in coverage and become more linear, a more
QLCS nature, as they progress downstream over eastern MN into
western WI. The main hazards initially will be large hail and
isolated tornadoes, but this will transition to a more damaging
wind/hail concern as the event progresses. So, this aligns well
with the SPC upgrading much of the coverage area to an Enhanced
Risk of severe thunderstorms for Friday and Friday night.

As the upper trough quickly pushes the front to the east late
Friday night through Saturday, this will bring an end to the
precipitation from west to east overnight through Saturday, with
some weak showers/thunderstorms lingering over western WI for much
of the day Saturday while the MN portion of the coverage area
clears out in the wake of the front.

As for temperatures/humidity, a muggy day is again expected for
Friday as highs reach the mid-80s for much of the coverage area
with dewpoints in the upper 60s to mid 70s. This will put heat
index values into the lower 90s potentially. Behind the front for
Friday night into Saturday, lows will drop into the mid 50s to
lower 60s followed by highs generally 75-80.

.LONG TERM...(Saturday night through Thursday)
Issued at 310 PM CDT Thu Aug 13 2020

For the long term, things are looking downright gorgeous. High
pressure will be in place for the period, keeping skies mostly
clear with light northwesterly winds. Temperatures will be
running near to slightly below average for mid August through the
period and dew points will fall back into the low to mid 50s.
Monday looks to be the coolest day of the week with highs in the
low to mid 70s, running about 5 degrees below normal for most of
the CWA. As the aforementioned high slides southeastward from
North Dakota across Minnesota Tuesday into Wednesday, light winds
will gradually switch around to the west and then southwest before
becoming southerly late in the day Wednesday. This will allow
temperatures and dew points to slowly creep back up toward August
normals by Wednesday and Thursday.

Precip chances remain slim until the middle of next week, but
models disagree on timing and placement, so only went with a low
chance of PoPs late Wednesday into Thursday for now.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1058 PM CDT Thu Aug 13 2020

Few changes needed to going TAFs, with current TAFs matching up
will with guidance coming in at 00z. Still some uncertainty with
how far southeast the southern tail of the line of storms
currently in northwest MN will build, but does look to come into
at least central MN. Kept TAFs VFR, though as we saw yesterday, as
diurnal cu-field gets going, plus the added moisture from the
decaying remnants of the NW MN convection, we could see a few
hours of MVFR cigs Friday morning, mainly for central MN. Only
real change noted with 00z guidance with respect to storm threat
Friday afternoon is the potential for a little less coverage of
storms from the Twin Cities on south.

KMSP...Still have a small threat of remnants of NW MN making it
down here around 00z, but this looks unlikely given the weak shear
and slow movements were are seeing now. The only advantage these
storms will have in their favor is the very unstable atmosphere in
place. Little has changed with thinking for TS threat Friday
afternoon, with around 00z look like when a broken line moves
through the MSP vicinity.

/OUTLOOK FOR KMSP/
Sat-Tue...VFR. Wind NW 5-10 kts.

&&

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

SHORT TERM...JPC
LONG TERM...Dye
AVIATION...MPG

Hazardous Weather Outlook
National Weather Service Twin Cities/Chanhassen MN
918 PM CDT Thu Aug 13 2020

MNZ041>045-047>052-055-057>059-150230-
Douglas-Todd-Morrison-Mille Lacs-Kanabec-Stevens-Pope-Stearns-
Benton-Sherburne-Isanti-Swift-Kandiyohi-Meeker-Wright-
918 PM CDT Thu Aug 13 2020

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

.DAY ONE...Tonight.

Thunderstorms will move into central Minnesota after midnight. A
few severe storms will be possible, with the main hazard being
damaging winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

A few lingering non severe thunderstorms will be possible into
Friday morning across central Minnesota.

Friday afternoon, thunderstorms are expected to develop in
western Minnesota, moving into eastern Minnesota and western
Wisconsin during the evening. Numerous severe thunderstorms are
possible with this activity with damaging winds and very large
hail being the primary hazards. A few tornadoes are also possible.
The severe weather threat will be greatest west of the interstate
35 corridor in Minnesota.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation will likely be needed Friday afternoon
and evening.

MNZ053-054-056-060>070-073>078-082>085-091>093-WIZ014>016-023>028-
150230-
Chisago-Lac Qui Parle-Chippewa-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-
918 PM CDT Thu Aug 13 2020

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

.DAY ONE...Tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

A few lingering non severe thunderstorms will be possible into
Friday morning across central Minnesota.

Friday afternoon, thunderstorms are expected to develop in
western Minnesota, moving into eastern Minnesota and western
Wisconsin during the evening. Numerous severe thunderstorms are
possible with this activity with damaging winds and very large
hail being the primary hazards. A few tornadoes are also possible.
The severe weather threat will be greatest west of the interstate
35 corridor in Minnesota.

.SPOTTER INFORMATION STATEMENT...

SKYWARN spotter activation will likely be needed Friday afternoon
and evening.

Special Weather Statement
National Weather Service Twin Cities/Chanhassen MN
113 AM CDT Fri Aug 14 2020

MNZ041-042-140700-
Douglas-Todd-
113 AM CDT Fri Aug 14 2020

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT NORTHEASTERN DOUGLAS
AND TODD COUNTIES...

At 113 AM CDT, strong thunderstorms were clustered 7 miles northeast
of Parkers Prairie, or 24 miles north of Alexandria, moving east at
35 mph.

Wind gusts up to 50 mph and half inch hail are possible with this
storm.

Locations impacted include...
Alexandria, Long Prairie, Staples, Browerville, Clarissa, Eagle Bend,
Carlos, Staples Airport, Bertha, Swanville, Hewitt and Miltona.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4637 9474 4635 9470 4636 9466 4628 9464
      4592 9464 4591 9539 4611 9525 4611 9514
      4637 9515
TIME...MOT...LOC 0613Z 275DEG 31KT 4624 9523

ETA