523
FXUS63 KARX 182343
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
643 PM CDT Fri Jul 18 2025

.KEY MESSAGES...

- Increasing moisture today, thunderstorms tonight (40 to 70%
  chance).

- More progressive pattern returns this weekend into next week,
  with multiple chances of precipitation.

- Trending warmer by middle of next week, with persistent
  ridging across the central CONUS.

&&

.DISCUSSION...
Issued at 132 PM CDT Fri Jul 18 2025

Tonight: Heavy Rain, Strong to Severe Storms Possible

A surface low currently over the central South Dakota/Nebraska
border will provide an area of focus for storms later today as
southerly flow is allowing for larger scale moisture return
across the Plains and Upper Midwest. Storms are expected to
develop in the Southwest Minnesota/Eastern South Dakota region
late this afternoon into the early evening hours. As a
southwesterly LLJ strengthens across the Central Plains into
Iowa, more upscale growth is expected into an MCS. How this MCS
develops and propagates remains a point of contention among the
CAMs. Overall, the 18.12 HREF is leaning towards the stronger
storms staying to our west with a more southeasterly movement
out of SW Minnesota. The 12Z HRRR seems to be the main outlier
with a more easterly approach, leading the MCS directly over our
area (though more recent runs have leaned more southeasterly).
In any case, at least portions of our area are still subject to
see rain and storms move through our area during the overnight
period, with the CAMs also showing minor differences in how
quickly the MCS moves through. There is also significant
uncertainty as to whether this MCS will maintain its severity
through the overnight period or if it will gradually weaken as
it moves into our area. As such, our area remains in the Day 1
Marginal Risk for severe weather with too many unknowns, even
this close in time, as to how the threat will evolve once it
gets to our area. If we do see the severe threat maintained, the
main hazard would be the potential for damaging wind gusts.

Another hazard we will be watching is the chance for heavy
rains leading to flash flooding across portions of the area,
primarily Southeastern Minnesota and Northeastern Iowa. With the
aforementioned LLJ picking up through the evening, keeping a
steady supply of moisture and instability available,
backbuilding appears possible with the MCS. Pwats across the
area will increase to 1.5-1.75+ inches, allowing for efficient
rainfall processes. Given the saturation of soils and
potentially heavy rainfall rates, runoff leading to ponding or
possibly even flash flooding is a concern. The one thing that
will help is the anticipated progressive nature of the complex
by the time it approaches the region. With this in mind, WPC has
continued the Day 1 Slight Risk for excessive rainfall across
much of the region.

This Weekend: Low Rain Chances and the Warm Up continues

With the strong east/west oriented ridge holding firm this
weekend, our area will remain in zonal flow aloft. The
aforementioned surface low will trek east with a cold front
moving through the area during the morning hours of Saturday.
While this boundary is expected to be south of the area by
daybreak Sunday, it is expected to stall out across the Mid
Mississippi Valley. With shortwaves passing through the zonal
flow aloft and surface forcing with the stagnant frontal
boundary, low rain chances will persist for areas mainly south
of I- 90 on Sunday. Even with the cold front and northerly winds
expected on Saturday, temperatures this weekend will still be a
touch warmer than today with highs in the mid 70s to lower 80s.

Next Week: Active/Unsettled Pattern, Summer Heat/Humidity
Returns

The upper ridge will begin to amplify across the region as
troughing develops across Western Canada and the Pacific NW.
With our area in the crest of the ridge, this will lead to a
classic "Ring of Fire" set up. Shortwave impulses are expected
to eject out of the trough to the west and ride the ridge over
our area, setting off chances for precipitation, likely in the
form of MCSs. How strong the ridge becomes will play a factor
into where those MCSs propagate with a weaker ridge increasing
our chances of showers and storms. Cluster analysis shows EC
members favoring a stronger ridge which would lead to an
increase in temperatures and decrease in precipitation with the
MCSs propagating further to the north. The GFS is leaning in the
other direction which would favor slightly cooler temperatures
and more chances for rain. Details on rain chances and potential
storm severity will need to be fine-tuned over the coming days
as features become more well resolved in higher resolution
guidance.

With the expected ridging, temperatures will continue on their
upward trend into at least the middle of next week. Southerly
flow will not only allow for temperatures to climb back into the
mid to upper 80s by Tuesday, with lower 90s possible by across
our southern zones Wednesday into Thursday, but dew points will
also be on an upward trajectory. Current blended guidance has
dew points in the upper 60s to mid 70s for much of next week,
meaning head indices in in the mid, maybe even upper 90s, will
be possible. Again, this is a blended solution so if the ridge
is stronger, this could lead to higher temperatures and heat
indices across the region. While heat headlines are not
currently anticipated, it will be something to monitor going
froward.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 643 PM CDT Fri Jul 18 2025

Low-VFR to MVFR cigs will remain in place for the remainder of the
evening ahead of a round of showers and storms that push through the
region tonight and into Saturday morning. While much of the
CAMs have conflicting schools of thought with how convection
will evolve overnight and into early Saturday morning, have
opted to keep with some prob30 and prevailing mention for TSRA,
particularly during the 08-12z timeframe when confidence is
highest for any convection. IFR reductions are likely in any
thunderstorms during this period. As we head through the
morning, cigs likely (60-80% chance in the 18.12z HREF) fall to
low-MVFR to IFR heights before improving gradually through the
afternoon and into the evening on Saturday. Winds will begin the
TAF period at 5-10 kts from the south but will shift to
northwesterly during the later morning hours on Saturday as a
front moves through the area.

&&

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

&&

$$

DISCUSSION...Barendse
AVIATION...Naylor