Flash Flooding and Flooding in Wisconsin, August 27 to 28, 2020

Area Forecast Discussion
National Weather Service La Crosse WI
207 PM CDT Thu Aug 27 2020

.SHORT TERM...(This afternoon through Tonight)
Issued at 207 PM CDT Thu Aug 27 2020

Current surface analysis has a quasi-stationary frontal boundary
laid up from east central WI through southeast MN into central NE.
Area radars were showing a band of showers and storms along this
frontal boundary over east-central WI but things were relatively
quiet farther west where a decent cap was in place. Otherwise,
temperatures as of 2 pm ranged from near 80 across north central WI,
to the mid 80s/lower 90s south of I-90.

Could see some more shower/storm development as that frontal
boundary sags a smidge more south this afternoon -mainly east of the
Mississippi River. CAPE values are pretty respectable in the 2-
3KJ/Kg but shear seems a bit weak, peaking out around 20kt. Will
still have to watch for a few stronger storms mainly east of the
Mississippi River where the better CAPE pool will reside.

For tonight, will likely an uptick in thunderstorm development as
moisture transport increases ahead of an approaching mid-level
trough from the Northern Plains. Looks like the bulk of this
activity will again be east of the Mississippi before an MCS tied to
the main mid-level trough/PV tracks into the area toward morning.
This early morning complex of storms could be severe as it
approaches but is expected to wane before reaching us (west of the
Mississippi). Will have to keep an eye on this activity.

.LONG TERM...(Friday through Thursday)
Issued at 207 PM CDT Thu Aug 27 2020

Friday will see an enhanced risk of severe storms mainly south of I-
90 during the afternoon as CAPE builds and favorable bulk shear will
be present. Will have to watch there storms very closely for the
risk of damaging winds, large hail and isolated tornadoes.

Also, with precipitable water values sitting around 2 inches will
have to watch for heavy rainfall and possible localized flooding
through Friday.

Much more pleasant temperatures/humidity levels heading into the
weekend as Canadian high pressure pays a visit. Look for highs
Saturday and Sunday in the 70s with dewpoints in the 50s.

Push of warm air advection Sunday night ahead of a cold front across
the Northern Plains will bring a chance of showers/isolated
thunderstorms into the area. Look for the likelihood of showers and
isolated thunderstorms Monday as that front pushes through.

A digging mid-level trough of low pressure into the Upper Mississippi
River/Great Lakes regions will be seen for Tuesday into Thursday for
on and off shower/isolated thunderstorm chances. Look for highs in
the 70s with overnight lows mainly in the 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1252 PM CDT Thu Aug 27 2020

Frontal boundary laid up across the area this afternoon. Expecting
scattered to broken mid-cloud/bases above 7kft through the afternoon
at both KRST/KLSE. Could see a few storms form later this afternoon
mainly east of KLSE with daytime heating and the front in the
vicinity. Otherwise, better chance for storms will be
overnight/Friday morning as a stronger mid-level system pushes in
from the Plains. Will likely see storms roll into KRST around 10z
and into KLSE by 11z. Also could see some cloud vsby reduction into
MVFR with the thunderstorm activity. Looks like storms will clear
KRST by 15z but still scattered through 18z at KLSE.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...DAS

Hazardous Weather Outlook
National Weather Service La Crosse WI
427 AM CDT Thu Aug 27 2020

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-281200-
Mitchell-Howard-Winneshiek-Allamakee-Floyd-Chickasaw-Fayette-
Clayton-Wabasha-Dodge-Olmsted-Winona-Mower-Fillmore-Houston-
Taylor-Clark-Buffalo-Trempealeau-Jackson-La Crosse-Monroe-Juneau-
Adams-Vernon-Crawford-Richland-Grant-
427 AM CDT Thu Aug 27 2020

This Hazardous Weather Outlook is for portions of southeast
Minnesota...northeast Iowa and southwest into central Wisconsin.

.DAY ONE...Today and Tonight

Isolated strong to severe storms are possible this evening. A more
organized severe storm threat increases tonight with large hail
and damaging winds being the main hazards. Heavy rainfall may
lead to localized flooding within the Interstate 90 corridor.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Severe storms will be possible Friday afternoon into early
evening south of Interstate 90. Damaging winds, large hail, and
locally heavy rainfall are the main hazards.

Additional chances for showers and storms look possible Monday
into Monday night. It is too early to discern a severe weather
threat.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated at this time, but any severe
weather or rainfall reports would be appreciated.

.EMERGENCY MANAGEMENT COORDINATION...

No webinar is scheduled.

NMB

Special Weather Statement
National Weather Service La Crosse WI
1202 PM CDT Thu Aug 27 2020

IAZ008>011-018-019-029-030-WIZ054-055-061-272200-
Mitchell-Howard-Winneshiek-Allamakee-Floyd-Chickasaw-Fayette-
Clayton-Crawford-Richland-Grant-
Including the cities of Osage, Cresco, Decorah, Waukon,
Charles City, New Hampton, Oelwein, Elkader, Prairie Du Chien,
Richland Center, and Platteville
1202 PM CDT Thu Aug 27 2020

...Another Hot Afternoon for Late-August...

At mid-day, temperatures were climbing into the upper 80s under
sunny skies. With the humid conditions, heat index values will
soar into the 95 to 100 degree range this afternoon. River valleys
could experience heat index values to 105. Those values will be
in the shade, with added stress on the body if in the sun.

If working or playing outdoors, make sure you take breaks out of
the sun and drink plenty of water.

Baumgardt