FXUS63 KARX 160420

Area Forecast Discussion
National Weather Service La Crosse WI
1120 PM CDT Sun May 15 2022

.DISCUSSION...(This evening through Sunday)
Issued at 207 PM CDT Sun May 15 2022

Key Messages:

 - Cooler as work week unfolds

 - Rain chances midweek and again late week

 - Cooler next weekend

Through Monday:

Seasonable conditions are expected through the start of the work
week. A mid-level shortwave trough evident on GOES water vapor
imagery early this afternoon approaching from the plains will pass
across the Mid/Upper MS Valley through this evening, but much of the
precip should slide south of the area. A few of the CAMs want to pop
isolated showers across northern WI late today with diurnal heating
and some modest aid from an approaching trough in NW flow. Although
weak CAPE will build through peak heating, a dry/well mixed boundary
layer will limit instability and low-level convergence through early
evening will be very weak, so any showers would be isolated and
short-lived. A diffuse surface front will pass south overnight into
Monday resulting in cooler temps on Monday for northern areas, but
given the timing of the front and dry air in place, precip chances
look unlikely.

Midweek rain chances (Tue-Wed):

Heights aloft will begin to increase on Tuesday as broad upper
ridging over the nation`s midsection nudges into the area. However,
temperatures won`t see much of a response with a quasi-stationary
front sitting southwest of our forecast area over Iowa. A colder
850mb Canadian airmass will be grazing our northeastern counties
while the warmth and increasing moisture stay confined to our
southwest because of that boundary. Increasing frontogenetic forcing
may support isolated shower/storm activity mainly west of the
Mississippi River during the day, but the better forcing won`t
arrive until a couple shortwaves cross the region late Tuesday and
Tuesday night. This will introduce more widespread rain coverage
from late afternoon through daybreak Wednesday. During this time,
weak to moderate moisture transport looks to fan across our area,
nudging PWATs to near 1.3 inches. Weak MUCAPE will develop south of
I-94, enough to support some elevated convection. Drier air will
filter in from the northwest on Wednesday with upper flow briefly
turning more zonal. Cooler conditions persist with highs Tuesday and
Wednesday in the 60s to low 70s.

Late-week rain chances (Thu-Fri):

A short-lived jump in temperatures takes hold on Thursday as
progressive ridging amplifies overhead in response to a developing
trough over the Northwest. Associated upper low is progged to ride
the Canadian/US border Thursday into Friday with the surface low
lifting into northern Minnesota by Thursday evening. NAEFS indicates
a fairly deep surface low for mid-May, about 3 standard deviations
below the mean. Warm front and warm sector should lift completely
through our area during the day, though temperatures only look to
top out in the 70s to perhaps lower 80s. Moisture transport looks to
ramp up Thursday night ahead of the approaching cold front, with
some hints (mainly from GFS) of deeper warm cloud depths coming into
play with a low potential for PWATs exceeding 1.5" across our south.
Could therefore be some localized heavier rains, though amount of
convective instability is still in question that far out.

Weekend outlook:

Cold front looks to push through the area sometime early Friday with
potential for some wrap around showers into Saturday as cyclonic
flow persists into the weekend. Strong signal for cooling by next
weekend a Canadian airmass slips into the Upper Mississippi Valley /
Great Lakes regions.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1121 PM CDT Sun May 15 2022

VFR conditions are expected. Northwest wind gusts will kick in
during the late morning on Monday.


.FIRE WEATHER...(Today and Monday)
Issued at 207 PM CDT Sun May 15 2022

Elevated fire weather conditions are expected on Monday with low RH
and gusty NW winds. Deep mixing to near or above 800 mb with low-
level cold advection/unidirectional flow will result in NW winds of
10-20 mph with gusts to 30 mph. The deep mixing combined with temps
in the low to mid 70s will allow RH to fall to around 25-30% by
early afternoon for much of the area, potentially dropping as low as
20% by late afternoon for some areas. Cooler temps in the 60s across
north-central WI could help keep RH somewhat higher in the 30 to 40%





NWS ARX Office Area Forecast Discussion