342
FXUS63 KARX 050547
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1247 AM CDT Sat Jul 5 2025

.KEY MESSAGES...

- Warm into the evening with dry conditions outside of a
  isolated storm over central WI this afternoon.

- Several rounds of storms Saturday morning and again in the
  afternoon/evening. Main risk from these storms will be locally
  heavy rain and strong winds.

- Seasonal temperatures for next week--highs in the upper 70s to
  mid-80s--with periodic bouts of storms throughout the week.

&&

.DISCUSSION...
Issued at 135 PM CDT Fri Jul 4 2025

This Afternoon/Evening - Mostly Dry and Muggy

Early afternoon water vapor imagery shows longwave upper
tropospheric ridging sliding eastward across MN/WI with a
negatively-tilted Northern High Plains shortwave trough axis
impinging on its upstream flank. Meanwhile, broad southerly
surface flow is keeping a warm and moist Gulf air mass
(increasingly amplified this time of year by evapotranspiration)
anchored over the forecast area. A meridional wedge of drier
925-700-mb air over central MN advects eastward later today,
allowing for enough of a capping inversion to keep convective
initiation at bay for most holiday festivities.

The only area of concern is towards central Wisconsin (along
and north/east of I-94) where this cap arrives more towards the
evening and forecast profiles show 1500-2000 J/kg of CAPE with
little to no inhibition by 21Z. Visible satellite imagery hints
at some airmass discontinuity across western Wisconsin, likely
tied to the training storms that occurred last night. This very
weak boundary could be enough of a trigger to generate at least
isolated convection by mid-afternoon before the storm threat
shifts eastward with the building cap. Locally heavy downpours
and gusty winds would be the main threats with these storms.

Saturday - Several Periods of Storms

Saturday`s precipitation forecast is rather messy with at least
two main waves of showers and storms to contend with. The first
comes in the morning as an outflow dominant and decaying line
of convection roles in from the west and northwest. The main
question with these storms is the rate at which they decay, with
a slower decay rate resulting in more convective debris and
less airmass recovery in the afternoon. There is no strong
signal in the 04.12Z HREF as to which scenario will unfold, but
more members leave some residual showers around into the early
afternoon and the official forecast plays to that idea.

By the afternoon, a surface cold arrives from the northwest and
serves as the trigger for renewed thunderstorm development. The
strength of these cells hinges on the degree of heating that
can take place during the day, dictated by the earlier
convective trends. Hodographs will be compact and complex in
nature, resulting in quick upscale growth to lines or cell
clusters and a limited window for a given storm to become
severe. Interactions between these storms could locally enhance
threats for a short while and bear monitoring as we move through
the day tomorrow. Slower storm motions will once again result
in a heavy rain threat with any storm. Pockets of stronger winds
are also a threat with some of the more robust storms. These
threats wane in the evening as the front slides off to the
southeast.

Next Week - Seasonal with Several Rounds of Showers and Storms

A period of quasi-zonal flow results in steady temperatures
near seasonal norms (upper 70s to mid-80s for highs) for the
upcoming week and periodic rounds of showers and storms. While
it becomes increasing difficult to pin down exact rainfall times
as we move through the week, there is better confidence
(30-40%) in precipitation occurring Monday night into Tuesday.
Moving beyond this timeframe, the timing of the individual
perturbations becomes less reliable in the ensembles, resulting
in a smattering of lower end PoPs into next weekend. The is no
strong signal for an organized severe weather threat at this
time, but as is always the case this time of year, things can
change quickly based on how the previous day`s storms unfold.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1228 AM CDT Sat Jul 5 2025

Period of rainfall, associated MVFR conditions, and potential TS
arrives Saturday morning and looks to persist into the late
afternoon and early evening. While there is high confidence in
MVFR conditions being present, timing of TS at any given point
is less certain. Have therefore included multi hour PROB30
groups to illustrate the thunder potential. Future issuances
will focus on narrowing these periods of TS mentions.

&&

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

&&

$$

DISCUSSION...Skow
AVIATION...Ferguson