124
FXUS63 KARX 190538
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1238 AM CDT Thu Jun 19 2025

.KEY MESSAGES...

- Periods of showers and storms through Friday, with a
  conditional severe weather risk for Thursday and Friday
  afternoon/evening.

- Very hot and humid this weekend into early next week with
  afternoon heat indices of 100-105 and lows struggling to fall
  below the mid-70s.

- A potential multi-day heavy rain and river/flash flooding
  event looms on the horizon for next week.

&&

.DISCUSSION...
Issued at 1255 PM CDT Wed Jun 18 2025

This Afternoon: Scattered Showers and Storms

Scattered showers and thunderstorms persist for the afternoon
and expand in area with daytime solar insolation--albeit
tempered by mid to high clouds emanating from the low passing to
the south. These showers linger into the evening hours and
dissipate from west to east as upper level kinematic support
wanes with the passage of our meridional upper level trough.
Skies clear out tonight and set the stage for a nice morning on
Thursday.

Thursday - Friday: Conditional Severe Weather Risk

Broad longwave ridging builds into the region for Thursday and
Friday, but multiple undulations in the flow present windows in
which we could see convective development.

Where exactly convection initiates on Thursday afternoon/
evening is a bit uncertain, dependent on the strength of the cap
at peak heating. Most likely, storms will either initiate on
the edge of the warm nose in northwestern WI and drop southeast
while a second cluster of storms forms along the ribbon of
theta-e advection out in western MN and propagate
southeastward. There are also a few HREF members that develop
discrete convection in between these two regimes. Favorable
elongated hodographs aided by a 60-kt jet will allow for
organized storm structures, possibly even supercellular in
nature. Such wind profiles will be favorable for large hail
production if storms remain discrete. If storms form closer to
the linear forcing, they will grow upscale quickly into more of
a multi- cell clusters. Given the uncertainties in storm
initiation locations, it is tough to pin down how this event
will evolve. It does look like the better window for storms here
will be Thursday night into early Friday morning as the
upstream complexes move in.

For Friday, a stronger surge of theta-e advection lifts
northward through the region and serves as the focus for a
potential MCS to track across northern Minnesota and Wisconsin
Friday afternoon and night. It looks like this complex tracks
north of I-94 with areas to the south well capped as the heat
builds in, but there are still some low PoPs as far south as
I-90 to account for any delays in the front lifting northward.

End of the Week into Early Next Week: Hot and Humid!

The well-advertised heat remains on track for the weekend as a
deep longwave trough carves out the western CONUS and the
Southern Plains subtropical ridge spreads northeastward into the
Ozarks and Lower Ohio River Valley. There has not been much
change to the forecast over the last 24 hours with respect to
the forecast heat indices of 100 to 105 degrees. Record warm
lows are also on the table for this period with the NBM guidance
depicting mid to even upper 70s--several degrees above current
daily record warm lows. The warmth lingers into Monday, possibly
even Tuesday in southwestern Wisconsin depending on how our
rain pattern evolves next week.

Next Week: Multiple Rounds of Heavy Rain, Flooding Potential

We return to an active stretch of weather for next week, with
the concerns shifting to multiple rounds of heavy rain and
potential flash and river flooding. The synoptic ingredients are
coming together in the form of a broad corridor of
southwesterly upper level flow ejecting a multitude of weak
perturbations along a quasi-stationary boundary oriented
parallel to the 60-70-kt upper level jet. A wide open Gulf
brings ample boundary-layer moisture northward across the
central CONUS while mid-level Pacific moisture rides
northeastward ahead of the positively-tilted longwave trough,
boosting PWATs to 1.5-2+ inches for much of next week.

While the longer range solutions are locking into the synoptic
ingredients for repeated rounds of heavy rain, the devil is in
the details with exactly WHERE the near surface front lines up
each day next week. This will be driven to some degree by the
evolution of the previous day`s convection (making it difficult
to pin down QPF amounts exactly), but given the synoptic
blocking pattern, the front is not going to move very far. A
look at the individual members of the Grand Ensemble shows high
confidence (>90%) that this event will occur, it is just a
matter of where each round of rain falls.

An aggregate look at all the ensemble members depicts a swath
of 20-30% probabilities of 4+ inches of rain next week from
northern Iowa up into western Wisconsin. It is impressive to see
such a signal this far out from the event given the inherent
uncertainties that come with convective precipitation
forecasting and points to the synoptically-driven nature of this
event that is easier to forecast farther out in time.

The degree of flooding hinges on exactly where each round of
rain falls. If the rain falls over roughly the same locations
for multiple days, this increases the risk for flash flooding as
we move through the week. If the band shifts laterally in space
each day, the flash flooding risk may be mitigated. However,
with much of this rain falling in the Mississippi River drainage
basin, rises along local rivers and the Mississippi are more
likely.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1233 AM CDT Thu Jun 19 2025

VFR conditions expected at both TAF sites through the 19.06Z TAF
period. Should aviation impacts of TSRA occur, highest
confidence will lie in central Wisconsin. Could see a stray
shower as far south as KLSE but very low confidence. Winds turn
counter-clockwise through today, becoming west through the
afternoon and south-southwest towards the end of the 19.06Z TAF
period.

Widespread storm chances accompanying strong south-southwest
winds shortly after the 19.06Z TAF period. Line of storms sags
southeast through Friday morning. Expect TSRA mention in the
next couple of TAF periods.

&&

.CLIMATE...
Issued at 1255 PM CDT Wed Jun 18 2025

Record Warmth This Weekend (Record / Forecast):

  Maximum              Warm Low
June 21
La Crosse:    102 (1988) / 9474 (1943) / 78
Rochester:      99 (1988) / 9372 (1943) / 78

June 22
La Crosse:    97 (1995) / 9475 (1983) / 78
Rochester:     94 (1911) / 92        71 (1983) / 77

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Extreme Heat Watch from Saturday afternoon through Sunday
     evening for WIZ032-033-041-053>055-061.
MN...Extreme Heat Watch from Saturday afternoon through Sunday
     evening for MNZ079-086>088-094>096.
IA...Extreme Heat Watch from Saturday afternoon through Sunday
     evening for IAZ008>011-018-019-029-030.

&&

$$

DISCUSSION...Skow
AVIATION...JAR
CLIMATE...Boyne/JAR