Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 162325
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
625 PM CDT Mon May 16 2022

.DISCUSSION...(This evening through Monday)
Issued at 239 PM CDT Mon May 16 2022

Key Messages:

 - Increasing rain chances Tuesday-Wednesday

 - Thunderstorms, perhaps strong to severe, Thursday night

 - Much cooler this weekend with some frost potential

Rain Chances (Tonight-Tue):

A shortwave trough in progressive WNW flow will approach on Tuesday.
At the surface, a boundary likely will remain south of the area, but
models generally show showers trying to develop over part of the
area late tonight or Tuesday in a region of modest moisture
transport and 700 to 500 mb frontogenesis. However, model solutions
show differences in the strength/placement of the fgen forcing, and
given the antecedent dry air in place, there is some uncertainty in
coverage/timing of rain. Rather weak lapse rates/instability north
of the surface boundary should keep thunder chances on the low side
through the day on Tuesday. Temps will also hinge on extent of
clouds and rain with potential for some areas to climb into the 70s
if a drier, more deeply mixed solution verifies, especially east and
north.

Showers and Isolated Storms (Tue night-Wed):

A shortwave will be crossing the Upper Mississippi Valley Tuesday
night with favorable moisture transport directed into the area.
PWATs are progged to climb to around 1.25" south of I-90. A small
amount of MUCAPE (up to a few hundred J/kg) west of the Mississippi
River could support a few rumbles of thunder there. Frontogenetic
forcing looks to brush our far southwestern counties Tuesday
evening/night, so convective activity may be a bit more vigorous
just south of the area. While the area would benefit from a good
soaking rain, amounts only look to range from up to 0.1" north of I-
90 to 0.1 to 0.4" south of I-90. Any lingering rain looks to exit
our southeast Wednesday morning. Chance for some additional showers
to develop over northwest Wisconsin in the afternon, potentially
clipping Taylor and Clark counties.

Late-week rain chances (Thu-Fri):

A short-lived jump in temperatures is in store for Thursday as
broad, low amplitude ridging slides overhead. This will be ahead of
a deepening upper low/trough over the northwest CONUS that will
advance into the Northern Plains by Thursday evening. A surface low
will sit over South Dakota at daybreak with a warm front extending
eastward. This front will progress northward through the local area
during the day, with the low tracking into central Minnesota by
evening before lifting into Ontario overnight.

Moisture transport will ramp up heading into Thursday night ahead of
the approaching cold front. Models still differ on timing the
frontal passage (whether beginning late evening or early Friday
morning), but either way surface based storms will be unlikely with
convection developing sometime overnight. Models appear to be
suffering from a high dewpoint bias, which is typical for this time
of year. GFS gets quite bullish with dewpoints in the mid 60s and
MUCAPE >2500 J/kg overnight. This seems very overdone. ECMWF is more
tempered with dewpoints in the lower 60s, which is more reasonable
but still seems high for the setup. Thus, there remains some
uncertainty on potential storm intensity as the cold front comes
through. Even for elevated storms, there does look to be adequate
deep layer shear to perhaps support a few strong to severe storms
with hail and locally heavy rain as the main concerns. Plenty of
uncertainty that far out, but worth noting we`re outlooked in SPC
Day4.

Weekend outlook:

Secondary surface trough/cold front will drop through the area by
Friday evening in advance of the deep upper trough. Within the
resultant cyclonic flow, there could be showers at times for parts
of the area heading into the weekend, but nothing very organized.
The main story for the weekend will be return to much cooler
conditions as a broad surface high builds across the central CONUS.
A Canadian airmass will settle into the region on Saturday, though
with gradually moderating 850mb temperatures into Sunday. Still,
highs in the 50s/60s appear likely. Depending on cloud cover,
Saturday night could very well introduce a frost threat, perhaps
even a localized freeze concern in the typical cold spots.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 616 PM CDT Mon May 16 2022

VFR conditions will persist through much of the TAF period.

Wind gusts will subside here in the next our or two this evening
with loss of solar heating. Light winds less that 10 knots are
anticipated through the remainder of the period becoming more
easterly after 12z and briefly southeasterly around 18z. KLSE may
even be variable at times. Cloud coverage increases tomorrow
morning ahead of incoming rain showers. Was not confident on the
spatial coverage at this time, but did mention VCTS in the TAFs at
this time. Will continue to monitor and adjust as the event draws
near and confidence increases. KRST may be near MVFR ceilings at
the end of the TAF period.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

DISCUSSION...JM/Kurz
AVIATION...Peters


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