Special Weather Statement, NWS La Crosse, WI

Area Forecast Discussion
National Weather Service La Crosse WI
251 PM CDT Wed Apr 22 2020

.SHORT TERM...(This evening through Thursday)
Issued at 251 PM CDT Wed Apr 22 2020

When a strong warm front lifts only about halfway through your
forecast area in late April, you know it's going to be a fun
temperature forecast. And this warm front did not disappoint with
currently more than a 30 degree temperature spread between Medford,
WI (47F) and Charles City, IA (79F). Guidance has been pretty much
right on the money with the warm front losing its northward momentum
once it lifted into southeast MN. It currently stretches from
roughly Zumbrota, MN to Muscoda, WI with south to southwest flow on
the southern side and east to southeast flow to the north. Moisture
transport south of the front has remained rather weak, as dewpoints
are struggling to rise beyond the mid 40s across northeast IA and
far southwest WI. This is lower than the 50+ dewpoints models
originally suggested for today, so there hasn't been as much
instability thus far as was anticipated earlier.

Through the rest of this afternoon, the warm front will slowly be
pulled southward again as the surface low (currently sitting on the
MN/IA border) drifts ever so slowly to the southeast. A strong band
of 1000-925mb frontogenesis along the front will continue to favor
development of eastward propagating showers and storms along the
front, across mainly northeast Iowa into far southwest WI. Similar
to Monday's setup for gusty winds from the showers and storms,
today's low levels are again exhibiting an inverted-V sounding
profile due to the drier air in place. Resultant evaporative cooling
will help to further amplify the mixing down of stronger winds aloft
with any passing showers and storms. KMCW reported a 47 mph gust
just prior to 2 PM, likely tied to the developing showers there. A
tongue of 800-900 J/kg DCAPE extends from north-central IA into a
portion of NE IA. MLCAPE profiles are not all that impressive with
only 500-1000 J/kg to work with, so any hail that develops should be
small and sub-severe. Latest CAMs keep the bulk of activity this
afternoon into early evening south of the MN border and generally
south of Vernon County in WI, with the focus gradually shifting
eastward through this evening.

Heading into tonight the main forecast concern will be increasing
low clouds developing over eastern WI, advecting into our area
overnight courtesy of easterly flow. This combined with a very stout
inversion aloft will result in mostly cloudy or overcast skies for
the area through midday Thursday before clouds begin to slowly
erode. Some guidance wants to develop some light rain across eastern
portions of the forecast area on Thursday, but forcing looks pretty
weak and moisture very shallow. Could see potential for some
drizzle, but for now have kept forecast dry through the morning. The
HRRR and RAP do try to pop some diurnal showers across
southwest/central WI in the afternoon. Lows tonight will range from
30s north of I-94 to 40s elsewhere. Highs Thursday generally in the
upper 40s and 50s, perhaps a few 60s in our far south and west.

.LONG TERM...(Thursday night through Wednesday)
Issued at 251 PM CDT Wed Apr 22 2020

Shortwave energy pushes into the area Friday into Friday night,
bringing a chance for rain. With cloudy conditions Friday, highs
look to stick to the 50s for most. For Saturday, low pressure spins
up to our south in the vicinity of southern Illinois courtesy of a
shortwave ejecting northeast out of the southern plains. There is
some question as to the extent of interaction between this southern
feature and our departing northern shortwave, and a few models try
to paint some light QPF back across our south, so we will have to
watch for perhaps some light rain.

Active northwest flow aloft continues Sunday into early next week,
with models dropping a subtle shortwave somewhere in the region from
the northwest Sunday. Precipitation amounts, if any, look fairly
light at this time. Greater chances for precipitation come later
Monday through Wednesday, as better moisture works into the area and
one or more shortwaves and associated surface features move through.
Timing/placement differences remain, so broad low PoPs from the NBM
blend were retained. Temperatures look to remain near or slightly
below normal, with highs in the 50s and 60s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 100 PM CDT Wed Apr 22 2020

A warm front continues to slowly advance northeast early this
afternoon, already having pushed through RST. The front is expected
to slow down as it approaches LSE later this afternoon, not quite
making it there before surface low pressure over southern MN drops
into northern IA. This sagging low will then slowly pull the
front southward, which is expected to keep shower and storm
activity south of both TAF sites this afternoon/evening. Wind
direction will be variable this afternoon as the front and surface
low move through the region. On the northern side of these
features, east to northeast winds tonight will advect low clouds
developing over eastern WI into RST/LSE after 07Z Thursday. IFR
ceilings are then expected to persist through most of Thursday
morning before clouds start to slowly erode towards midday.

&&

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

SHORT TERM...Kurz
LONG TERM...Lee
AVIATION...Kurz

Hazardous Weather Outlook
National Weather Service La Crosse WI
359 AM CDT Wed Apr 22 2020

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-231200-
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-
359 AM CDT Wed Apr 22 2020

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

.DAY ONE...Today and Tonight

Scattered thunderstorms are possible from mid afternoon through
early this evening, mainly south of Interstate 90. A few could
produce gusty winds or small hail.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

No action needed.

.EMERGENCY MANAGEMENT COORDINATION...

No webinar is scheduled.

Special Weather Statement
National Weather Service La Crosse WI
220 PM CDT Wed Apr 22 2020

IAZ008>011-018-019-029-030-WIZ054-061-222015-
Clayton-Floyd-Winneshiek-Chickasaw-Howard-Fayette-Allamakee-Mitchell-
Crawford-Grant-
220 PM CDT Wed Apr 22 2020

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN
MITCHELL...SOUTHERN HOWARD...NORTHWESTERN CLAYTON...NORTHERN
FAYETTE...ALLAMAKEE...NORTHEASTERN FLOYD...SOUTHERN WINNESHIEK...
CHICKASAW...NORTHWESTERN GRANT AND CRAWFORD COUNTIES...

At 219 PM CDT, radar indicated strong thunderstorms were located
along a line extending from near Waucoma to near Farmersburg.
Movement was east at 40 mph.

Wind gusts up to 50 mph are possible with these storms.

Locations impacted include...
Decorah, Prairie Du Chien, Waukon, New Hampton, West Union, Boscobel,
Fennimore, Postville, Monona, Calmar, Fredericksburg, McGregor,
Ossian, Elgin, Clermont, Elma, Hawkeye, Lawler, Marquette and
Spillville.

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 4333 9080 4292 9063 4291 9219 4331 9279
TIME...MOT...LOC 1919Z 271DEG 36KT 4309 9197 4293 9143

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Special Weather Statement
National Weather Service La Crosse WI
316 PM CDT Wed Apr 22 2020

IAZ010-011-019-029-030-WIZ054-055-061-222115-
Clayton-Winneshiek-Chickasaw-Fayette-Allamakee-Richland-Crawford-
Grant-
316 PM CDT Wed Apr 22 2020

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHWESTERN CLAYTON...
NORTHEASTERN FAYETTE...ALLAMAKEE...WINNESHIEK...EAST CENTRAL
CHICKASAW...NORTHERN GRANT...SOUTHWESTERN RICHLAND AND CRAWFORD
COUNTIES...

At 315 PM CDT, radar indicated strong thunderstorms were located
along a line extending from near Calmar to near Prairie Du Chien.
Movement was east at 30 mph.

Wind gusts up to 50 mph and penny size hail are possible with these
storms.

Locations impacted include...
Decorah, Prairie Du Chien, Waukon, Lansing, Boscobel, Fennimore,
Postville, Monona, Calmar, McGregor, Ossian, Marquette, Spillville,
Fort Atkinson, Harpers Ferry, Ridgeway, Hardin, Westport, Excelsior
and Preston.

LAT...LON 4309 9211 4321 9209 4321 9208 4327 9208
      4335 9207 4335 9049 4290 9055
TIME...MOT...LOC 2015Z 263DEG 24KT 4323 9183 4307 9109

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