242
FXUS63 KARX 151052
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
552 AM CDT Sat Aug 15 2026

.KEY MESSAGES...

- Showers linger through the early morning hours (20-40%) ahead
  of a cold front that moves through this afternoon bringing
  additional showers and storms (30-50%).

- Drier conditions are expected Sunday and Monday with high
  temperatures in the upper 70s to low 80s.

- Shower and storm potential increases again Tuesday into
  Wednesday (50-80%).

&&

.DISCUSSION...
Issued at 1236 AM CDT Sat Aug 15 2026

Today: Periods of Showers and Storms

Ongoing scattered showers across portions of southeast Minnesota and
western Wisconsin associated with a band of 850-700hPa theta-e
advection come to an end overnight as said band continues moving
northward. Further south, nebulous 900-800hPa warm air advection
spreads through northeast Iowa and southwest Wisconsin during the
early morning hours with some scattered showers already ongoing.
These showers have greater potential to continue through the early
morning hours (20-40%), but little to no impacts expected.

Heading into this afternoon, a 500hPa shortwave trough lifts
northeastward out of the Central Plains, forcing a cold front
through the Upper Mississippi River Valley. Instability builds
across the region along and ahead of the front with MLCAPE reaching
750-1250 J/Kg, greatest south of I-90 and west of the Mississippi
River, supporting convective development across the region as the
boundary moves through (30-50%). CAM guidance has consistently been
suggesting storm coverage along the front should be more isolated to
scattered in nature, likely due to some weak capping across much of
the Upper Mississippi River Valley as seen in model soundings.
However, given the combination of the wave aloft, forcing along the
front, and evident instability, thinking the environment should be
able to overcome the weak capping resulting in some greater
shower/storm coverage this afternoon.

While strong/severe potential is very low (<5%) with any convective
development due to 0-6km bulk shear of 15kts or less, some fairly
efficient rain rates are possible given the juiced-up atmosphere
that remains in place across the Midwest. As has been the case over
the past several days, PWATs near 2in, warm cloud depths of 10kft+,
and skinny SBCAPE profiles will support some instances of rainfall
rates upwards of 1 in/hr. Since we`ve largely missed out on the
heavy rainfall over the past few days, flooding concern is very low
as the front moves through. That said, some local areas of ponding
seem reasonable where the heaviest rain falls.

Sunday - Monday: Drier, Near Normal Temperatures

With the cold frontal passage tonight, a much drier airmass is
ushered into the Midwest bringing relief from the persistent
pattern of precipitation. High pressure will be the dominant
feature across the region resulting in partly cloudy skies to
end the weekend and start the new week. Some breezier northwest
winds look to be on the table Sunday afternoon as cold advection
steepens 0-1km lapse rates with 20-25kts of wind atop this
layer. That said, not expecting gusts to be overly impressive,
generally only 15-25mph. Stronger winds shift east as we head
into Sunday night while high pressure and low level ridging take
hold. Clearing skies and light winds are currently expected
across the region during this period which could result in a
night of valley fog, though low level saturation may be a
limiting factor given the drier airmass. Monday looks to be a
repeat of Sunday albeit with lighter winds. High temperatures
top out in the upper 70s to low 80s both days, around normal for
this time of year.

Tuesday - Wednesday: Increasing Shower and Storm Potential

A more zonal upper level pattern will be in place across the United
States Tuesday into Wednesday. A jet streak and associated 500hPa
shortwave trough over the west coast early Tuesday will be able to
quickly translate eastward through the day along this zonal flow and
force a cold front through the Upper Mississippi River Valley.
Shower and storm potential increase along this front, sitting around
50-80% in the 15.01z NBM. There does appear to be some potential for
some stronger storms during this period as 70-90kts winds associated
with the aforementioned jet streak increases 0-6km bulk shear to
around 40-50kts along with MUCAPE 1000-2000 J/kg present across the
region. AI/ML guidance also continue to suggest there is some
probability for strong/severe weather during this timeframe so it`ll
remain a period to monitor.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 552 AM CDT Sat Aug 15 2026

MVFR to IFR reductions this morning will persist through the
afternoon as low-level moisture remains in place across the region.
Cigs may improve to low-VFR by late afternoon and into the evening,
however, probabilities in the NBH and deterministic guidance favor
category reductions again after 06z. Showers and storms will be
possible (30-50%) during the late afternoon and evening hours with
MVFR to IFR reductions possible underneath any storms. Fog formation
may be possible (10-30% chance in the recent HREF for IFR vsbys) as
well depending on how cloud cover trends manifest Saturday night and
into Sunday morning. Winds will being the TAF period from the
southeast but will shift to northwesterly and generally remain
around 5-10 kts.

&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...Naylor