Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 201944

Area Forecast Discussion
National Weather Service La Crosse WI
244 PM CDT Tue Apr 20 2021

.SHORT TERM...(This evening through Wednesday)
Issued at 244 PM CDT Tue Apr 20 2021

Forecast area remains under cold cyclonic flow aloft. Steep lower
level lapse rates under this cold pool was producing widespread
cumulus and scattered rain/snow showers. Otherwise, it was chilly
with readings at 1 pm in the low/mid 40s.

Partial clearing expected tonight with showers waning by mid/late
evening. Plan on cold overnight lows in the upper teens/lower 20s
in the sandy/bog areas of central WI, and the mid 20s elsewhere.

More of the same for Wednesday -becoming mostly cloudy by
afternoon under cold cyclonic flow overhead with isolated to
scattered rain/snow showers. Look for highs once again in the 40s.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 244 PM CDT Tue Apr 20 2021

It appears the next several days will have some occasional
precipitation chances into early next week, but at this point,
there does not look to be any big systems on the horizon. After a
dry and warmer day Thursday, thanks to some upper level ridging,
the first of these precipitation chances will arrive for Thursday
night into Friday. The upper level ridging will quickly move off
to the east of the region ahead of an approaching short wave
trough. The latest models are all in pretty good agreement that
this wave will have decent amplitude as it emerges from the
Rockies but looks to weaken and become pretty flat by the time it
is moving across the Upper Midwest. As a result, the forcing looks
rather weak with only some very weak pv advection in the 500-300
mb section and this should primarily move past to the northwest of
the area. The low level moisture transport also looks to be
weakening with the dissipation of the short wave trough with some
extremely weak moisture return into the area. With some weak
isentropic up glide in the warm air advection zone, there could be
just enough lift to generate a few showers. The small
precipitation chances will then continue Friday night into
Saturday as a cold front get pushed through the region as a
northern stream trough and short wave trough swing across the
region. Again, the forcing looks to be rather weak and with the
moisture transport focused on a system going across the Gulf Coast
States, would only expect some scattered activity.

A period of upper level ridging is expected to be over the area
to close out the weekend before moving past early next week. The
next best chance for precipitation then looks to be Monday night
into Tuesday as southwest flow aloft develops. The models are
suggesting there could be some short wave troughs that come out of
an upper level low moving across the Desert Southwest. This
should allow and area of low pressure to form somewhere over the
Plains and then advance east. As it typical with southwest flow
system, the models vary greatly on timing of when the surface
system may move into the area which impacts whether there will be
any precipitation chances or not. Given that this is several days
away, plan to include at least a chance of precipitation starting
Monday night to honor the faster model solutions.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1218 PM CDT Tue Apr 20 2021

VFR cumulus in abundance across the area again this afternoon.
Could also see a few showers of rain/rain mixed with snow, or, all
snow but no restrictions in vsby expected. Look for the shower
threat t diminish later this evening but picking up again by later
Wednesday morning into the afternoon, especially east of the
Mississippi River. Look for VFR cloud cover to continue through
Wednesday as well. Otherwise, prevailing northwest winds over the
next 24 hours, gusting 15-20kt in and near any shower activity.




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