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000
FXUS63 KARX 192242
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
542 PM CDT Fri Apr 19 2024

.KEY MESSAGES...

- Chilly start to the weekend with temps near/below freezing
  expected for many locations tonight and Saturday night.

- More seasonable by Sunday into next week with the next more widespread
  rain chances (60-80%) late Monday into Tuesday.

&&

.DISCUSSION...
Issued at 153 PM CDT Fri Apr 19 2024

Tonight-Sunday: Chilly start to the weekend

A cumulus field has thickened this afternoon beneath cooler mid-
level air on the southern flank of an upper level trough across
Ontario, especially north of I-90. The combination of steep low-
level lapse rates and a few embedded shortwave perturbations
dropping southeast late today into the evening around the
parent trough could yield a few snow or rain showers (10-30%),
with the higher chances heading northward. With deep mixing,
occasional wind gusts have reached 40-45 mph in open areas.
Winds will subside gradually this evening.

A seasonably chilly airmass will remain in place into the start of
the weekend with low-level cold advection persisting and northwest
flow aloft. Temps should begin to moderate by Sunday with plenty of
sunshine and warming 925 mb temps. Elevated fire weather conditions
are possible on Sunday with RH potentially falling to 20-25% and
deep mixing above 850 mb. Boundary layer flow does not look overly
strong, but some gustiness is possible with diurnal mixing.

With the cooler airmass, frost/freeze will be a concern through
Sunday night, with tonight/Saturday nights the coldest. High
probabilities (>90%) exist across most areas tonight for freezing
temps with the higher chances (50-90%) for temps below 28F centered
west of the Mississippi River, on ridgetops, and areas north and
east of I-94. With some mixing/wind overnight, conditions may not be
ideal for true frost development, but it will be chilly regardless.
Given the temperatures, we issued a Freeze Warning for our counties
we have activated for frost/freeze headlines so far this spring,
based upon vegetation susceptibility.

Monday-Tuesday: Shower chances

A healthy Pacific shortwave trough remains on track to impact the
region later Monday through Tuesday. Some showers will be possible
by Monday in association with mid-level warm advection leading the
parent wave, with additional chances into Tuesday or even Tuesday
night as the associated front/trough slides through, dependent on
the timing of the trough. Overall, moisture transport/instability
look modest, likely limiting thunder chances (20%) and higher rain
amounts. As it stands now, global ensembles (EPS/GEFS/CMC) show
around 40-60% chances for 1/4" of rain near and north of I-90 with
lower (20-30%) chances for at least 1/2" of rain in this area. Very
few members show 1" amounts. Fairly seasonable temps are expected
ahead of the system.


Wednesday-Friday: Seasonable, rain chances late week

In the wake of the early week trough, broad, progressive mid to
upper level ridging will spread east across the Upper Midwest for
mid to late week. Overall, the airmass looks seasonable for late
April (50s and 60s), with some modest warming through late week.
There is a signal for increasing shower/storm potential towards the
end of the work week as the ridge axis passes east and deeper
moisture lifts back north across the Upper Mississippi Valley.
Predictability of shortwave passages within the southwest flow
pattern remains lower, but NBM precipitation chances are medium (40-
70%) by Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 535 PM CDT Fri Apr 19 2024

As solar heating diminishes tonight, expect stratocumulus to
diminish across the area. While gusty winds are expected to
diminish overnight tonight, there will likely be intermittent
gusts as the boundary layer doesn`t completely decouple. On
Saturday, winds veer from WNW to NW with gusts in the 20 to
25kt range throughout the day. Expect another day with a low-end
VFR stratocumulus deck across the region. There is a 20 to 30%
chance for high-end MVFR ceiling between 10 and 15Z Saturday
morning, but will leave out of the TAF at this time.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Freeze Warning from midnight tonight to 8 AM CDT Saturday for
     WIZ032-033-041-053>055-061.
MN...Freeze Warning from midnight tonight to 8 AM CDT Saturday for
     MNZ079-086>088-094>096.
IA...Freeze Warning from midnight tonight to 8 AM CDT Saturday for
     IAZ008>011-018-019-029-030.

&&

$$

DISCUSSION...JM
AVIATION...JAW