133
FXUS63 KARX 172301
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
601 PM CDT Tue Jun 17 2025

.KEY MESSAGES...

- Periods of showers and storms from this afternoon through
  Friday. Locally heavy rainfall will be the main threats today
  and Wednesday south of I-90, with a conditional severe weather
  threat for Thursday and Friday.

- Hot and humid for the weekend with heat indices of 100-105
  degrees.

- Wetter pattern looms on the horizon for next week.

&&

.DISCUSSION...
Issued at 155 PM CDT Tue Jun 17 2025

Today - Wednesday: Periods of Storms, Locally Heavy Rain

Weak 925-700-mb return flow is streaming northward over western
Iowa early this afternoon with light showers developing on the
edge of this theta-e advection wing. This forcing gradually
lifts NNE through the afternoon, through it has been moving
slower than earlier progged and have trimmed PoPs for this
afternoon and evening to south of I-90. Any convective cells
that do form will be nearly stationary but short-lived given
the weak flow from the surface to 500 mb. Locally heavy
rainfall will be the main impacts with these cells with the raw
output from the various HREF members depicting speckles of 1-2
inches of rain under these cores.

A meridional shortwave advances off the High Plains tonight
into Wednesday morning, pulling a diffuse cyclone off the Front
Range and up the surface baroclinic zone into southern Great
Lakes. The region will sit on the north side of the low, keeping
the severe threat at bay. However, periodic showers will fester
for much of the region through the day within the corridor of
synoptic ascent (aided by daytime solar insolation) before the
upper trough clears in the evening. Rainfall amounts in
northeast Iowa and southwest Wisconsin could push 1-2 inches
closer to the low during the day, but this should be the main
impacts from any showers or storms.

Thursday - Friday: Several More Rounds of Storms, Some Severe?

Confidence in the evolution of the convective pattern degrades
for Thursday into Friday as the midweek shortwave departs to the
east and shallow ridging builds in its wake. The medium range
solutions are coming in slightly more progressive with the ridge
on Thursday, resulting in the surface baroclinic zone staying
further north and a stronger cap over the forecast area.
Convective initiation would be favored over western or northern
Minnesota in the afternoon on Thursday, likely dropping to the
southeast towards our area Thursday night into Friday morning
with the possibility of additional cells developing along the
surface front/convective outflow Friday afternoon.

On Thursday afternoon, given the presence of a 60-70-kt jet
streak and favorable cyclonically-elongated hodograph
trajectories, any cells that do manage to break this cap closer
to our area will be capable of supercellular structures and
large hail. The big questions revolve around the thermodynamic
profiles and whether any storms can realize this favorable shear
alignment. Moving into Friday, the front orients itself more
parallel to the upper level flow and the threat will increase
for training cells and heavy rain.

Given the poor intra and inter-model variability with
convection over the last week, it is difficult to ascertain any
further details at this stage in the forecast. The PoP forecast
remains a broad-brushed 40-50 percent that will be fine-tuned
over the coming days.

Saturday - Sunday: Hot and Humid

We will see a brief break from the precipitation for the
weekend, only to have it replaced by a stretch of summertime
heat. A deeper longwave trough carves out the western CONUS and
the Southern Plains subtropical ridge spreads northeastward into
the Ozarks and Lower Ohio River Valley. This should lift the
surface baroclinic zone northward and allow warmer air to build
into the region for the weekend.

The latest trends in the guidance have been favoring a more
humid and warm airmass, pushing forecast afternoon heat indices
into the 100-105 degree range for Saturday and Sunday along and
south of I-90. Record warm lows are also on the table for this
period with the latest NBM guidance depicting mid to even upper
70s--pushing past the current records. This heat does not last
long with the main vort lobe pulling to the northeast and
dropping a boundary southeastward for Sunday night into Monday
and shunting the warmer air to the southeast.

Next Week: Return of Rain

Looking ahead to next week, subtropical ridging becomes
reestablished from Texas into the lower Great Lakes and lingers
through the end of the week. Southwesterly flow anchors over the
region with multiple weak upper level undulations propagating
along a quasi-stationary surface boundary. This will bring
repeated rounds of rainfall to the region and increase the risk
for flooding. How this threat unfolds will depend on nuances in
the pattern that we are still many days from resolving, but at a
minimum the synoptic setup looks to be in place to support
heavy rainfall.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 558 PM CDT Tue Jun 17 2025

VFR conditions currently present across the terminals. Showers
and storms have developed across Northern Iowa and extend into
our local area along and south of the MN/IA border. Hi-
resolution CAMs continue to keep this early convection south of
the RST terminal so have left rain out of the near-term forecast
and added PROB30s later with increasing but still generally low
chances for rain. MVFR visibilities and wx obstructions in the
form of light rain and mist should become more prevalent after
09Z. Though the axis of heavier precipitation looks to stay
south and east of the RST terminal, low chances for rain/storms
continue into tomorrow afternoon until early-evening before
decreasing below PROB30 thresholds. LSE should be more squarely
in the axis of precipitation with higher confidence in showers
late overnight through tomorrow afternoon. Near-term adjustments
may be needed, especially for RST, should the showers move
further north than expected or continue to move slower than
guidance. NW winds are expected to stay below 10 kts at both
terminals before becoming NNE for Wednesday.

&&

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

&&

$$

DISCUSSION...Skow
AVIATION...Barendse