816
FXUS63 KARX 091823
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
120 PM CDT Wed Jul 9 2025

.KEY MESSAGES...

- Scattered showers, storms Thursday (20-40%). Some storms could be
strong.

- Rain likely Friday (70-80%) - locally heavy. Storm chances, but
uncertainties in placement/timing of the various weather elements
lowers confidence in coverage and strong (severe?) potential.

- More rain chances moving into next week, but also starting to
trend a bit cooler by mid week.

&&

.DISCUSSION...
Issued at 120 PM CDT Wed Jul 9 2025

> THU: shower, storm chances

A few weak disturbances look to interact with branches of the 850 mb
jet/moisture transport late tonight over the plains. Thunderstorm
clusters will result, tracking eastward. The storms will be exiting
the primary instability axis and some waning/decrease in coverage-
intensity should occur. That said, the NAM holds that convection
through the morning, "picking up" into the afternoon. Kind of an
outlier at this time - but can`t be discarded out of hand.

While the storms are favored by most CAMS to be decreasing, the
resulting MCVs will be present and tracking over the upper
mississippi river valley for the afternoon/early evening. The CAPE
pool is progged to creep into western WI by that time and the RAP
suggests the 850 mb jet could reassert itself into eastern MN by
late afternoon. RAP pushes SBCAPES past 3500 J/kg, but also suggests
sfc Tds in the lower 70s. A bit too much on both counts. The HRRR
sits around 2K J/kg SBCAPE and looks more reasonable.

Mixed signals on whether a low level cap would remain in place
through the day, but most of the CAMS spark at least a smattering of
convection moving through the afternoon. Where is uncertain, highly
dependent on where the convection sparks tonight, and then that
resulting MCV(s) tracks. As a result, will paint chances broadly,
hoping to refine as we move into tomorrow.

For the storms that do initiate, little if any wind shear to aid
updrafts/storm development. Enough instability for a stronger storm
or two.


> FRI: periods of rain, locally heavy at times. Some storms - but
how widespread and how much of a strong (severe?) risk is uncertain.

How Friday and Friday night eventually playout is becoming more
"messy" as a plethora of both large and small scale features are
going to play roles. What does remain more "clear" is that there
will be periods of rain for the local area - with the potential for
locally heavy rain.

First, the upper level shortwave that has been well progged to kick
out of the southern Rockies Thu night, heading east/northeast to
across the local region Friday, has been trending more south. Could
be in reaction to the expected convection Thu, that lingers into Thu
night. Could also then run along a west-east running warm front that
is nudged south by the Thu night pcpn. The shortwave slated to drop
southeast out of southern Canada Friday still holds its
timing/placement, helping to edge a sfc cool front east of the local
area Sat morning.

Pool of instability (3.5+K J/kg SBCAPE) pools across IA northern IL,
but how far north that will extend is in question - with that warm
front positioning the likely marker. Much like the instability,
shear will depend on which side of the front you are on. Deeper,
stronger in the warm sector, much less north of there. Increased
severe risk in that overlap - and whether that touches southern
parts of forecast area is a question that can`t be answered (yet).

As previously alluded to, confidence remains high in the ability of
the atmosphere to produce locally heavy rain: strong 925:850 mb
moisture transport northward (esp Fri night), PWs of 2+", and warm
cloud depths of 4+ km. Pcpn mostly north-south in orientation and
transitory will work against time/residence concerns, but localized
urban flooding possible. QPF in the GEFS and EPS close with their 25-
75% suggesting 1/2 to 1 1/4". However, their high end outliers are
2+" in the GEFS and 3+" in the EPS.


> NEXT WEEK: Shot for rain Tue, trending cooler.

Solid agreement in the bulk of the GEFS and EPS for sliding an upper
level trough across northern parts of the region in the Tue/Wed time
frame. A cold front is drug along with the trough and most of the
ensemble members drop some QPF from the combo of the forcing and
summer airmass.

The upper level pattern becomes more northwesterly post the trough
and as a west coast ridge amplifies. Cooler, less humid air is
promised in this scenario. While there is a fair amount of variance
in resulting temps, 75% of the EPS and GEFS members favor below
normal temps starting by the middle part of next week, potentially
persisting into the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1250 PM CDT Wed Jul 9 2025

VFR conditions remain this afternoon into tonight with light
northerly winds today veering to become south to southeasterly this
evening and overnight. Convection expected to be ongoing across the
Great Plains this afternoon moves eastward towards southeast
Minnesota and northeast Iowa overnight, allowing for low
probabilities (20-30%) of scattered showers and thunderstorms west
of the Mississippi River in the morning hours. However, not overly
confident in impacts to the TAF sites given uncertainty in the
evolution of the convection as it moves eastward, so have left
mentions out of the TAFs with this issuance.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...Falkinham