903
FXUS63 KARX 121034
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
534 AM CDT Mon May 12 2025

.KEY MESSAGES...

- Elevated fire weather conditions expect today along and north
  of I-90. Avoid outdoor burning.

- Showers and thunderstorms a good bet (40 to 80%) Thursday into
  Friday, especially north of I-90. Severe storms could occur
  Thursday, but many key details to realize this risk remain
  unclear.

&&

.DISCUSSION...
Issued at 329 AM CDT Mon May 12 2025

Elevated to critical fire weather conditions today:

Today, upper ridging aloft remains in place over the Upper Midwest,.
with warm temperatures aloft and abundant sunshine leading to
temperatures rising into the 80s, well above normal for mid-May. Lee
pressure falls to our west in MT should help maintain a modest
surface gradient. Resultant mixing should lead to dry conditions
and therefore elevated fire weather conditions where winds
manage to become strong enough. Have leaned forecast highs above
NBM and moved dewpoints to the dry side of the distribution in
deference to expected mixing. See the dedicated fire weather
section below for more information.

Showers and storms Thursday into Friday, potential severe Thursday:

After a couple weak shortwaves eject northwestward around an upper
low to our south try to kick off a few showers and thunderstorms
Tuesday and Wednesday, a strong upper wave approaches from the west
Thursday. With a jet streak advancing over the central Plains on the
equatorward side of this feature Wednesday night, surface
cyclogenesis should occur, helping to advect low level moisture
northward. Unlike Tuesday/Wednesday, when modest moisture results in
anemic CAPE profiles, suggesting any updrafts will struggle,
potential for 2000+ J/kg of MLCAPE appears in the cards if the upper
wave arrives during the afternoon hours. Progged soundings suggest
capping in the 700-800mb layer is a potential limiting factor, so
current thinking is that the upper wave will need to arrive
somewhere around peak heating for parcels to overcome this
impediment and for widespread convection to develop. Should this
occur, severe storms would be possible given aforementioned
instability and favorable deep layer shear. Given the strong upper
dynamics, ML output is understandably ramping up for this period.
However, still plenty of uncertainty about if the opportune window
for convection plays out - and if it does so in our CWA - so will
continue to closely monitor this period and refrain from ramping up
messaging at this time.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 531 AM CDT Mon May 12 2025

VFR conditions expected for the next 24 hours. Similar to
yesterday, winds out of the south will pick up through the
morning. RST will see gusts to near 25 kts this afternoon with
both sites seeing winds diminish during the evening hours while
backing more to the southeast.

&&

.FIRE WEATHER...
Issued at 329 AM CDT Mon May 12 2025

Today, modest surface pressure gradient winds and efficient
mixing due to clear skies should once again lead to dry
conditions across the area with most locations seeing relative
humidity dropping below 25 percent. Given this and the abundance
of cured fine fuels per forecast GLFF FFMC values, entire region
is at play for elevated to critical conditions. Limiting factor
is once again wind speeds as, even with efficient mixing, winds
aloft are not particularly strong. All in all, a similar setup
to yesterday, when RH values fell even farther than expected
and, for areas west of the Mississippi Valley in SE MN,
critical conditions were reached for several hours due to gusts
of 25 mph or greater per RST/TOB obs. However, progged winds at
the top of the mixed layer are a couple knots lighter for today.
Indeed, 12.00z HREF probabilities for gusts of 25 mph are about
10 percent in Dodge/Olmsted Counties. Therefore, have once
again gone with elevated conditions along/north of I-90 and
refrained from issuing a Red Flag Warning west of the MS valley
in SE MN.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Barendse
FIRE WEATHER...Ferguson