634
FXUS63 KARX 201148
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
648 AM CDT Sat Jul 20 2024

.KEY MESSAGES...

- Slight precipitation and storm potential for some today,
  highest confidence along western and northern periphery.

- Similar conditions through new week: diurnally induced storm
  potential with a low possibility for anything severe.

&&

.DISCUSSION...
Issued at 230 AM CDT Sat Jul 20 2024

The dry conditions come to a close for some today, eventually. The
trough seen on WV imagery early this morning with weakening
energy struggle to eradicate and saturate the dry air in place.
Have gone with a slightly drier forecast as a result.

Rain & Storm Chances Today:

Initial saturation along our western periphery this morning is
associated with a surface low well to the southwest. With the trajectory
of this low, expect precipitation potential to remain along our
western periphery through this evening. Subsequent
precipitation chances early this afternoon sag south from
northern Wisconsin as the upper level trough traverses the Upper
Mississippi River Valley; dragging a back door cold front with
it. While mid to upper level lapse rates steepen from the upper
level low, a low to mid level temperature inversion and lack of
forcing limits overall confidence and coverage in precipitation
and storms. Southwest extent of precipitation potential will be
main forecast challenge albeit overall limited impact. Any
storms that do form will remain isolated and short lived with
little to no shear to work with; pulsing up and down with heavy
rain as a primary hazard.

Through The New Week:

The upper level low lingers through the new week, sending
perturbations around its periphery, perpetuating daytime
precipitation and storm chances locally. Long range ensembles
(GEFS/EPS/GEPS) all exhibit associated waves of 0.01"+ 100%
probabilities through the week. Coincidental timing of these
meager perturbations and peak diurnal heating will dictate best
storm potential. Investigating individual members, most contain
some semblance of SBCABE during the first half of the week
concurrent with diurnal heating before eroding it for the second
half. Long term (ECMWF/GFS) soundings show minimal concurrent
shear, limiting any confidence for severe potential.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 630 AM CDT Sat Jul 20 2024

Showers are moving from west to east through the morning hours.
Subsequent showers and accompanying storms sag south from
northern Wisconsin early this afternoon. Highest impacts
therefore initially reach northeast Iowa and southeast
Minnesota this morning, spreading into central and west-central
Wisconsin during the afternoon. Extent and magnitude of impacts
remain in question as low level dry air will challenge overall
saturation. KRST TAF site will remain on eastern edge of showers
and potential IFR ceilings while KLSE TAF site will remain on
southwestern edge of showers and storms in central Wisconsin.
Have sided optimistically in both TAFs as trends have been
forecasting low level dry air mostly abating saturation. Storm
potential remains quite scattered so haven`t included in either
TAF at 20.12Z issuance however cannot be ruled out.

Subsequent concern will be flight restrictions overnight into
Sunday morning. High resolution forecast models suggest
widespread LIFR with low level stratus and fog. Given lingering
higher clouds, dropping temperatures to saturation remains
unlikely.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...JAR