006
FXUS63 KARX 070834
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
334 AM CDT Mon Jul 7 2025

.KEY MESSAGES...

- Storm chances overnight through Tuesday morning. Scattered
  cellular storms through Tuesday.

- Storm chances return overnight Thursday through Friday.

&&

.DISCUSSION...
Issued at 302 AM CDT Mon Jul 7 2025

Storm Chances Tonight Through Tuesday:

Building heights usher in a dry forecast today with low level
moisture transport firing off convection in the Northern Plains.
This line of convection follows a perturbation advecting east-
southeast over the Canadian border on early morning water vapor
imagery loops into tonight. High resolution model guidance agrees
on a weakening trend as storms approach the Upper Mississippi
River Valley late tonight into early Tuesday morning concurrent
with the loss of diurnal heating and weakening moisture transport
which can be attributed to splitting of synoptic forcing. The
resultant split of higher confidence in precipitation (50%) chances
passes to the north and south of the forecast area; tied to the
better forcing from the aforementioned trough to the north and higher
low level moisture transport and a subsequent Rocky Mountain
Low to our south. The overnight timing limits overall
instability, i.e. limiting storm potential.

Precipitation chances increase through early Tuesday morning along a
weak frontal boundary as the lagging trough axis passes by. This weak
forcing/boundary will limit shear and subsequent storm potential.
Any frontal passage becomes washed out with diurnal heating which
also keeps pop up storms possible through Tuesday. Increased instability
with little to no deep layer shear keeps storm chances to a cellular
mode. Thus, nothing in the way of severe expected.

Dry Midweek; Storm Chances Thursday Night through Friday:

Building mid level heights (LREF) provide a /mostly/ dry midweek
with higher precipitation chances returning overnight Thursday
into Friday morning. Strongest low level moisture transport
lifts through the Central to Northern Plains on Thursday,
potentially grazing precipitation chances along our western
peripheral counties in northeast Iowa and southeast Minnesota
Thursday night.

Disagreement in LREF cluster analysis stems from the strength of
Tropical high pressure and resultant peripheral eastern extent
of low level moisture penetrating through the Mississippi River
Valley. Regardless, higher precipitation chances greet the
Upper Mississippi River Valley overnight through Friday morning.

Storm chances accompany frontal passage through Friday as a long wave
trough with an axis bifurcating the central CONUS advects
east.Much to be ironed out still as LREF cluster probabilities
for 1000 J/kg of MU/SBCAPE vary widely due to variation in
location and depth of said trough. Regardless of the behavior
(i.e., amplification) of the trough, clusters show a comma head
of 0.5" mean rainfall from the Northern through the Southern
Plains. Lastly, the high res PANGU, machine learning severe
weather models keep higher probabilities(15%) for severe to our
south and west.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1217 AM CDT Mon Jul 7 2025

Main aviation concerns will be fog potential early this morning.
Clearing skies have met temperatures to dewpoint temperatures
across much of Iowa into southern Minnesota. Although, little to
no FG observations outside of western Iowa. Have continued
previous mention in TAFs given the light wind setup and this
temperature trend. Expect an immediate term amendment to account
for exact timing.

VFR expected through most of the TAF period. Subsequent impacts
with incoming precipitation expected near the end of the TAF
08.06Z TAF period.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...JAR