072
FXUS63 KARX 212357
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
657 PM CDT Mon Jul 21 2025

.KEY MESSAGES...

- Smokey skies will gradually improve through the day.

- Low confidence on storm potential today through Tuesday.
  Better confidence (50 to 80%) in Wednesday night into
  Thursday.

- Warmer for Tuesday and Wednesday with heat indices from 90 to
  105F possible. Higher confidence (80 to 100%) in warmest
  temperatures occurring on Wednesday.

&&

.DISCUSSION...
Issued at 156 PM CDT Mon Jul 21 2025

Smokey Conditions Today, Maybe Tuesday Morning?:

With surface high pressure overhead today, smoke from Canadian
wildfires will continue to lower visibilities through the afternoon.
While an improvement is expected as far as near surface smoke
conditions, latest HRRR smoke guidance has a slight uptick in the
near surface smoke for Tuesday morning that may cause hazy skies and
potentially some impacts to visibilities. All smoke potential is
expected to leave the forecast area by Tuesday afternoon.

Storm Potential Through the Week:

Shortwave ridging continues over the Upper Midwest through midweek.
A surface boundary is expected to position itself over the western
portions of our CWA during the afternoon, as is evident in the theta-
e advection during that time period. If any storms do fire, they
would favor locations along and west of the Mississippi. Heading
into tonight the surface boundary lingers and some showers and
storms will be possible as the boundary gradually shifts eastward.
Meanwhile, the HRRR extended runs from 21.00 and 21.06Z showed a MCS
developing over southern Minnesota/northern Iowa. This model was the
only one showing it, however the 12Z run has gone away with the MCS
and replaced it with some isolated showers and storms. Some of the
other CAMs, as well as the HRRR, show a separate MCS that moves
through north central Minnesota and northern Wisconsin Tuesday
morning. This looks to mostly impact areas north of I-94, however
depending on where potential storms fire today and where the
boundary sets up will influence storm potential for the overnight
and how far south the Tuesday MCS gets. There is still some
uncertainty on the timing of this MCS as some models have it mid
morning and others have it towards the later morning/early
afternoon. By Tuesday night, another shortwave arrives in the Upper
Midwest bringing shower and thunderstorm potential, to our northern
counties, especially in Wisconsin. A couple of CAMs (NAM Nest and
HRW-FV3) have a line of storms pushing through the CWA Tuesday
afternoon into the evening. Then early Wednesday morning another MCS
looks to move through northern Minnesota and northwest Wisconsin.

By Wednesday night/Thursday morning, a deeper shortwave trough
pushes through the Upper Midwest, giving the area a better chance at
seeing widespread rain. Then immediately after this, the upper level
pattern shifts back to a zonal/slight west-northwest flow allowing
for periodic shower and thunderstorm chances through the weekend.
Overall, confidence in the thunderstorm potential is tricky and
dependent on previous MCSs and where surface boundaries set up each
day. The severe threat for each day is expected to be fairly
localized and dependent on where the convection occurred the
previous day and where any boundaries are located at.

Anomalous Warmth Midweek:

Strong warm air advection moves into the forecast area for both
Tuesday and Wednesday as southwest flow aloft increases. This
corresponds to above normal temperatures for both days. Latest EFI
values for Wednesday include much of the area in the 0.7 to 0.9
values for high temperatures, as well as much of the forecast area
in the 0.8 to 0.9 range for the overnight low temperature Wednesday
night into Thursday. What these higher values indicate are
anomalously warm temperatures compared to the climatological period.
Current forecasted high temperatures for Tuesday are in the mid 80s
for most and by Wednesday, the highs increase into the upper 80s to
low 90s. Heat indices for areas west of the Mississippi River are
roughly in the 95 to 100F range. By Wednesday, much of the forecast
area are in the 100 to 105F range.

Current NBM probabilities for greater than 92F are between 50 and
80% for areas along and east of the Mississippi River. There is some
uncertainty with how warm we get on Tuesday despite the warm
southwesterly flow based on storm potential and cloud cover.
Wednesday has the higher confidence as far as anomalous warmth goes.
The latest NBM 25th to 75th percentiles are quite confined, ranging
from roughly near 90F to near 95F respectively. Will continue to
fine tune these temperatures as current guidance has much of the
forecast area in heat advisory criteria for Wednesday.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 645 PM CDT Mon Jul 21 2025

MVFR ceilings, currently present along and west of a RST-OLZ
line, will slowly expand over the next several hours with these
eventually covering the entire forecast area. Additionally,
areas along and west of the Mississippi River, roughly a ONA-PVB
line, should see at least a bit of IFR ceilings during the
09z-15z time frame. There is potential for MVFR/IFR fog as
well, mainly along and west of an RST-OLZ line, but confidence
is too low for inclusion at this time. Finally, occasional MVFR
visibilities may occur areawide due to smoke originating from
distant wildfires. On the subject of thunderstorms, while these
cannot be ruled out entirely (10% chance at various times over
the next 24 hours) there is a slightly better chance (15-30%)
along and east of a ONA-Y51 line late in the period. Winds over
the next 24 hours will tend to be out of the south with some
gusts to 25 knots possible after 18z along and west of an RST-
OLZ line.

&&

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

&&

$$

DISCUSSION...Cecava
AVIATION...Ferguson