386
FXUS63 KARX 222314
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
614 PM CDT Fri Aug 22 2025

.KEY MESSAGES...

- Showers and storms will be possible (20-40% chance) later this
  afternoon and into the evening. Some storms may be strong with
  gusty winds and small hail possible.

- Temperatures trend much cooler this weekend through Tuesday
  with highs in the 60s to lower 70s. Morning low temperatures
  will be in the 40s and 50s.

- Small shower chances (10-20%) persist through the weekend with
  minimal rainfall amounts expected at this time.

&&

.DISCUSSION...
Issued at 1254 PM CDT Fri Aug 22 2025

Today: Showers and Storms Possible This Afternoon

The 500mb flow pattern is well depicted on GOES-19 water vapor
imagery and 22.15z RAP 500mb heights this afternoon as two trough
systems work through the Upper Midwest. The first of these currently
is transversing through MN that had a weakening MCS associated with
it and the second remains in southern Canada that will eject a cold
front towards the area overnight. As we continue through the
afternoon, questions remain on exactly how contaminated the
environment will be for convective initiation will be. Currently,
the recent RAP/HRRR sounding profiles would suggest that some MLCAPE
(1000-1500 J/kg) will be present. However, given the convective
debris moving in from the aforementioned remnant MCS, this may
temper any convective development to some degree. Additionally, the
forcing appears somewhat nebulous as low-level flow remains mostly
westerly throughout the afternoon with little convergence present.
As a result, convective coverage in the CAMs is fairly isolated
later this afternoon and into the evening. As far as severe
potential would be concerned with these, the relatively skinny
instability would suggest that storms will be slow developing, now 0-
6km bulk shear increases marginally later into the evening as the
upper-level trough begins to push closer to the area. However, with
mid-level lapse rates only being around 6.5C/km and MUCAPE values up
to 2000 J/kg, would think that hail under 1" in diameter would be
more probable with any stronger storms, even if warm cloud depths
are relatively shallow.

Saturday - Tuesday: Unseasonably Cool, Small Shower Chances

By the time we reach daybreak on Saturday, a cold front associated
with a pronounced, upstream upper-level trough will push through the
area and usher in a cooler and drier Canadian airmass from the
northwest. Consequently, there continues to be a strong signal for
temperatures to trend cooler than normal beginning this weekend and
continuing into early next week with the inter-quartile range in the
grand ensemble (GEFS/EC/Canadian ensemble) for high temperatures
ranging from the lower 60s to lower 70s across much of the region.
The 22.00z EFI would additionally support these unseasonably cool
temperatures with 80 to 90 probabilities for high temperatures
outside of EC model climatology.

As far as precipitation chances are concerned, cyclonic flow with
embedded shortwaves coupled with very shallow diurnal instability
atop the mixed layer will bring some shower chances into the picture
for the weekend. Overall there is a fairly robust footprint for some
measurable rainfall on Sunday as deterministic guidance
generally swings a pronounced shortwave into the region on
Sunday afternoon/evening. Currently, the grand ensemble
(GEFS/EC/Canadian ensemble) has high probabilities for
measurable precipitation during this period, thus have increased
precipitation probabilities for Sunday from the national blend.
Cannot rule out some sprinkle/shower activity on Saturday as
well with a similar setup albeit with the forcing less
favorable.

Wednesday - Thursday: Slowly Warming

As we move into the second half of the upcoming work week, the
aforementioned upper-level trough will very slowly push its way
eastward allowing for some upper-level ridging to try and sneak its
way into the region. Consequently, noticing some increase in
temperatures by mid-week with median high temperatures returning
into the 70s in the grand ensemble (GEFS/EC/Canadian ensemble)
starting on Wednesday.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 612 PM CDT Fri Aug 22 2025

A 2-4 kft cloud deck over the region clears out from west to east
this evening, with an isolated shower prior to 03Z. Overnight
winds of 5-10 kts veer from the WSW to the NW after 06Z. Winds
increase from the NW during the morning on Saturday to 10-
15G20kt by midday.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...Skow