083
FXUS63 KARX 152334
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
634 PM CDT Tue Jul 15 2025

.KEY MESSAGES...

- Showers and storms impact the region, mainly after midnight
  tonight through Wednesday evening.

- Locally heavy rainfall is the main concern with these storms,
  through some will bear watching for a severe potential in the
  early afternoon in SW Wisconsin.

- Cooler to end the week with highs more typical of the first
  day of fall on Thursday, slowly moderating through the weekend
  and back to average for early next week.

&&

.DISCUSSION...
Issued at 140 PM CDT Tue Jul 15 2025

Tonight - Wednesday Evening: Storm Details

Despite being less than 24 hours away, questions linger on the
coverage and intensity of storms that move through the region later
tonight into Wednesday. Storms initiated sooner and farther south
that the 15.12Z HREF members predicted in west-central Minnesota,
casting doubts on how these models will handle the evolution of
storms as we head through the afternoon and evening. Surface-based
inhibition is not overly strong this evening across southeast
Minnesota and western Wisconsin, so in theory an outflow boundary
shooting southeastward from these cells could trigger new
development sooner and farther east than forecast. The good news is
that the deeper shear lags on the cool side of the surface boundary
over northern Minnesota, keeping the risk for organized convection
at a minimum. Nevertheless, storms could produce locally heavy
rainfall if they manage to hold together.

This brings us to Wednesday. All of the 15.12Z HREF members decay
the main slug of overnight convection by the time it reaches our
forecast area near sunrise. The rate of decay varies among the
models, but residual convective debris should be in place during
the morning on Wednesday. The surface cold front arrives in
southeast Minnesota in the morning with a low riding up the
front during the morning, passing through the area during the
midday hours and moving into southern Wisconsin during the
afternoon. This only provides a narrow window for severe weather
before the threat shifts off to the east. However, the presence
of the weak surface flow near the low and the wind shift could
be a region that sees landspout processes IF we are able to get
enough solar insolation and near-surface instability before the
flow switches to the northwest.

There is higher confidence that locations along the north of I-90
will see periods of heavy rain in the de-facto deformation zone
to the north of the surface low. A look at the LPMM progs from
the HREF show corridors of 1-2 inches of rain with pockets of
3-4 inches in some of the worst-case scenario members. Probably
not enough to result in too many river problems, but poor
drainage areas may be susceptible to flooding. The complex as a
whole departs quickly Wednesday evening with CAA setting in
Wednesday night.

Thursday - Friday: Cooler and Drier

The end of the work week will be characterized by a period of cooler
and drier weather more typical of mid-September as a shot of polar
air grazes the region with the passage of a 1020-mb surface high.
Overnight lows will be driven by the degree of cloud cover and could
fall into the mid-40s (the NBM 10th percentile) Thursday night in
favored spots east of the Mississippi if conditions align perfectly.

The Weekend into Early Next Week: Moderating, Rain Returns

A mostly zonal flow pattern sets up for the weekend and into early
next week with multiple weak undulations in the upper flow driving
the risk for showers and storms. The surface baroclinic zone is
progged to set up somewhere from the Siouxland on east/southeast,
which would serve as a corridor for storms to track during the
weekend. A number of medium range members are showing one, possibly
two MCSs propagating down this boundary Friday night/Saturday
morning and again Saturday night into Sunday. The details on the
tracks and impacts from these systems will be refined as we approach
the event, but they would likely bring moderate to heavy rain if
they do manifest themselves.

Low predictability risks for showers and storms dot the forecast for
the start of next week with little change in the upper level
pattern. Where the surface baroclinic zone hangs up each day will be
the focus for higher rainfall amounts. While the forecast is covered
with 20-30% rain chances, a look at the individual ensemble members
shows that these values are simply driven by the wide spread in the
location of this boundary and most locales and times should be dry.
With the zonal flow, temperatures recover to seasonal values by
early next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 634 PM CDT Tue Jul 15 2025

VFR conditions are expected into the overnight as a line of showers
and storms weakens and largely remains north of I-90 with only a low
chance (20%) for precipitation to reach KRST prior to sunrise.
Towards mid-morning, a surface low pressure system will begin to
move into the region bringing both lowering cigs to MVFR/IFR heights
and bring widespread vsby reductions from showers and any embedded
thunderstorms. Winds will shift to northerly as the surface low
passes, however low-MVFR/IFR cigs will persist through 00z
Thursday with the 15.18z HREF having high probabilities (40-90%)
for cigs to remain at MVFR and medium probabilities (20-60%)
for IFR cigs after showers and storms pass during the afternoon
on Wednesday.

&&

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

&&

$$

DISCUSSION...Skow
AVIATION...Naylor