036
FXUS63 KARX 302358
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
658 PM CDT Thu Jul 30 2026

.KEY MESSAGES...

- Widespread rain tonight through Friday with highest amounts,
  1 to 2.5" with locally higher amounts possible, focused in
  southeast Minnesota and northeast Iowa. Otherwise 0.25 to 1"
  of rain expected for the rest of the forecast area.

- Seasonable temperatures with highs in the upper 70s to mid
  80s and mostly dry conditions from Sunday into Tuesday.

- Rain chances (25 to 45%) return Tuesday evening.

&&

.DISCUSSION...
Issued at 124 PM CDT Thu Jul 30 2026

Tonight-Friday: Heavy Rainfall

The longwave trough situated to our east will shift off to the east
this afternoon. Shortwave ridging moves into the Upper Midwest for
the day and at the same time, a shortwave trough begins to develop
across the northern Plains. As this trough shifts southeastward, it
will deepen. At the surface, a low forms this evening and progresses
southeastward through the overnight tonight and through the day on
Friday. With southwest flow advecting in PWATs between 1.7 and 2.2",
which corresponds to the 90 to 97.5 percentiles based on the
NAEFS, combining with the good moisture convergence, there will
be ample lift and moisture for a heavy rain event to unfold. The
good news is that due to our position to the north of the low
and the timing of when the low begins to impact our CWA, limited
to no instability is expected to build in. Further south into
central Iowa, they will have a break in between the first wave
of rain and when scattered storms develop. A low tornado risk is
possible down there due to the very low LCLs around 1000ft or
less and the amount of low-level shear (around 20 to 30 kts of
0-1km shear) and if enough clearing happens. The only way any
part of our CWA sees a low tornado risk is if the track of the
low shifts further north, allowing portions of the area,
probably northeast Iowa, to have that low tornado potential
(<5%) due to the previously mentioned conditions in central
Iowa.

Focusing on the heavy rain potential, EFI values have a swath of 0.7
to 0.85 across southeast Minnesota and northeast Iowa and into far
southwest Wisconsin indicating that this has the potential to be on
the higher side of climatological normal. There is also a SOT up to
1.5 for northeast Iowa, which indicates some guidance is showing
amounts up to 5". The probabilities for >1" in the GEFS have
continue to increase over the past couple of days with values of 60
to 70% in southeast Minnesota and northeast Iowa. Meanwhile the EPS
has a 80 to 100% chance for the same areas. There are differences in
the exact track of the low which will influence where the highest
totals end up. Another point to mention is the warm cloud depth
layer, around 4000m, that will help increase rain amounts. Model
guidance continues to show an initial wave of showers and maybe some
storms move through the area during the overnight and early morning
Friday, followed by either continued stratiform rain (for areas
north of the low) or more scattered showers/storms (for areas near
and south of the low). In general, 1 to 2.5" is expected across
southeast Minnesota, northeast Iowa, and far southwest Wisconsin.
Areas north of I-90 in Wisconsin are expected to receive between
0.25 to 1". Locally higher amounts are possible, potentially up to
5" for portions of southeast Minnesota and northeast Iowa. These
expected amounts remain uncertain due to the exact track of the low
and the fact that there is little to no instability in place to help
boost rain rates. At the same time there is the deep warm cloud
layer that would boost rain amounts. Overall heavy rain is expected
across portions of the Upper Midwest, favored in southeast Minnesota
and northeast Iowa.

Saturday-Thursday: Seasonable Temperatures with Dry Conditions
Early, Rain Chances Later in the Week

Ridging builds back in through early next week keeping the region
dry into Tuesday. Ensemble and deterministic guidance both support a
trough impacting the Upper Midwest for the latter portions of next
week. This would increase shower and storm chances starting Tuesday
(25 to 45%). There are uncertainties with when this trough moves
through the region, for instance the GFS is now slower than the
ECMWF in bringing the next bout of rain. It is now more on Wednesday
than Tuesday. Temperatures across the forecast period remain
seasonable with highs largely in the upper 70s to mid 80s. The lone
exception is Friday where highs will only get into the upper 60s to
mid 70s.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 653 PM CDT Thu Jul 30 2026

Heavy rainfall will be the main aviation impact through the
31.00Z TAF period, progressing from west to east through much of
Friday. While heaviest rainfall rates will likely cause periods
of IFR visibilities, specific timing for stronger forcing
driving heaviest rainfall rates remains forecast challenge.
Therefore, inclusion of TEMPO IFR at both TAF sites will likely
require further fine-tuning in coming forecasts.

MVFR-IFR ceilings eventually progress from west to east through
Friday and are expected to exit overnight through Saturday
morning. While TS isn`t included in TAF at current forecast hour
due to overall limited airmass instability, scattered TS still
remains possible (25%) through the daytime hours.

&&

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

&&

$$

DISCUSSION...Cecava
AVIATION...JAR