366
FXUS63 KARX 171856
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
156 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 /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1240 PM CDT Tue Jun 17 2025

Predominantly VFR conditions are forecast for this afternoon
into tonight, with small pockets of MVFR visibilities with any
slower moving showers/storms later this afternoon and evening
along and south of an AUM to DLL line. These showers spread
northward after 06Z, though confidence in how far north is
uncertain given recent trends that have shifted the rain further
south. MVFR ceilings are progged to spread into NE Iowa and
SW Wisconsin towards sunrise on Wednesday. Winds will be under
10 kts for the forecast period from the NW this afternoon and
the NNE for Wednesday.

&&

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

&&

$$

DISCUSSION...Skow
AVIATION...Skow