368
FXUS63 KARX 080609
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
109 AM CDT Tue Sep 8 2026

.KEY MESSAGES...

- Showers and storms likely beginning tonight and continuing
  through early Wednesday. Rainfall amounts of around 1/2" to 1"
  are expected with locally higher amounts possible. Some storms
  may be strong with gusty winds and small hail possible.

- Additional precipitation potential (30-60%) for late Friday
  and into Saturday.

- Near normal temperatures are expected throughout the week with
  a possible cool down by late in the weekend.

&&

.DISCUSSION...
Issued at 1258 PM CDT Mon Sep 7 2026

Tonight - Tuesday: Showers and Storms Likely

Precipitation chances will be on the rise overnight and into Tuesday
as a pronounced 500mb trough pushes through south-central Canada
tonight and into Tuesday. As this occurs, a surface low pressure
center with a trailing front will move through the local area and
increase precipitation chances. In addition, a fairly profound axis
of 850mb moisture transport pushes through the region advecting
precipitable waters up to around 2 inches into the region as shown
across deterministic guidance. As a result, the recent HREF has
fairly high probabilities (50-70%) for rainfall amounts over 0.5"
across portions of north-central WI and northeast IA. This is due to
the fact that the initial round of precipitation is favored
generally north of I-94 with the initial front and a second
potentially further where the front remains slower. As far as
severe weather potential is concerned, confidence is fairly low
in the potential as the better instability axis is generally
collocated with the 850mb moisture transport axis which remains
largely west of the local area. In addition, the speed max with
the with the upper-level jet streak remains well to the west of
the local area. Consequently, much of the deep-layer shear is
absent with bulk shear values generally remaining under 30 kts
based on RAP soundings. However, given the marginal DCAPE up to
900 J/kg along the front coupled with weak instability, cannot
rule out some strong to marginally severe storms capable of
producing strong wind gusts. Generally the aforementioned front
exits the region by Wednesday morning and into the afternoon.

Wednesday - Thursday: Drier, Near-Normal Temperatures

As we head into Wednesday and Thursday, northwesterly flow builds
into the region aloft with surface high pressure moving into the
region in the wake of the aforementioned front. Consequently,
expecting relatively precipitation free conditions during this
period of the forecast. However, in spite of the frontal passage,
not expecting temperatures to budge much with zonal flow and upper-
level ridging attempting to build into the region. As a result, NBM
generally keeps highs in the upper 70s to lower 80s through the end
of the work week.

Friday - This Weekend: Rain Chances, Potentially Cooling Down

By the time late Friday and the weekend rolls around, a pronounced
upper-level trough will move through the Upper-Midwest bringing
additional potential for precipitation Friday night and into
Saturday. Ensemble guidance is fairly enthusiastic about some
precipitation during this time frame as the grand ensemble
(GEFS/EC/Canadian ensemble) has fairly high probabilities (50-80%)
for measurable precipitation during this timeframe. Overall not
impressed with the severe potential with this round of precipitation
as the timing is not overly favorable with the precipitation moving
in overnight and instability being relatively lackluster. However,
given some AI/ML guidance shows some small probabilities (~5%
chance) Friday night and into Saturday for severe weather, cannot
rule it out if the timing of this system ends up being slightly
faster. Otherwise, in the wake of this trough passing through the
region, the potential exists for northwesterly flow to entrench
itself over the region resulting in some cooler temperatures late
into the weekend. However, given the wide range in high temperatures
by Sunday in the NBM with the 10-90th percentile ranging from the
middle 60s to lower 80s, confidence remains fairly low in exactly
how much modification to our summertime airmass this troughing
regime will do.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1254 AM CDT Tue Sep 8 2026

Immediate impact of LLWS expected to progress east over the next
couple of hours with frontal boundary passage. Subsequent storm
impacts continue through the overnight and early Tuesday morning
hours, temporarily abating through the early afternoon before
returning through the evening.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...JAR