679
FXUS63 KARX 291752
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1252 PM CDT Wed Jul 29 2026

.KEY MESSAGES...

- Rain returns on Friday with remaining questions focusing on
  just how much rain occurs. At least 1" seems like a good bet
  (75-83%) with a tail risk (5%) for a localized 5"+ total.

- Friday also brings a very small (<2%) risk for a tornado.

&&

.DISCUSSION...
Issued at 1251 PM CDT Wed Jul 29 2026

Rainy Friday

WIth a ridge firmly in place over the southern Plains, disturbance
currently over the Sierra Nevada looks to advance northeastward
over the northern Plains and then southeast over our CWA on Friday.
This wave should amplify as it does so given upper support from a
zonal upper jet over MB/ON and a weak upper jet advancing from OR to
over NE. As this occurs, surface high developing in the OH Valley in
the wake of a slowly departing upper low currently over the
Northeast Corridor will set up southerly winds across the
Mississippi Valley, leading to an increase in moisture. By 12z
Friday, PWATs may (20-50%) exceed 2" along and south/west of
Interstate 94, close to the climatological maximum in the DVN RAOB
record. This will lead to a swath of moderate rain from MN/IA into
WI/IL. Within this swath, rain amounts will very likely (75-85% per
29.06z NBM) exceed 1" with a low risk (20%) to exceed 3" and a tail
risk (1-5%) for a stray 5" total. Main disagreement across guidance
is on the exact north/south location of the upper wave and,
consequently, the location of higher rainfall amounts. GFS/GEFS
continues to remain farther south - putting heaviest rain south of
our CWA - compared to the EC and first available runs of the NAM are
roughly in between these two camps. Given this and the richly moist
air mass, not enough agreement across guidance on the position of
the upper low to discount a risk for moderate to heavy rain in our
CWA, with the risk for this relatively higher across northeast Iowa
and diminishing greatly along and north/east of Interstate 94. High
resolution guidance should cover the entire rain period over the
next 1-2 update cycles so hopefully confidence in placement will
increase soon.

Friday could also bring a risk for a stray tornado as southerly
winds at the surface underlay westerly winds at 850mb and above,
reflected in quickly turning hodographs in the low levels with
sufficient sfc-500m SRH for a tornado. However, multiple things will
have to come together to realize this - the main wave needs to
arrive in the afternoon during peak heating and precipitation in the
southerly warm advection needs to have breaks in it. Otherwise,
instability will be minimal, an outcome borne out by virtually all
model soundings which, unsurprisingly, stick with a close to moist
adiabatic profile given the high end moisture setup. Will have to
keep this in mind, but the risk appears very low (<2%).

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1229 PM CDT Wed Jul 29 2026

High clouds from convection over the High Plains will move into
the area overnight and linger across the area on Thursday
morning. With light winds overnight and climatology, would
expect some dense valley fog develop in in the Wisconsin and
lower Kickapoo river valleys.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Boyne