Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

000
FXUS63 KARX 152347
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
647 PM CDT Fri Mar 15 2024

.KEY MESSAGES...

- Near-critical fire weather conditions for Saturday with winds
  gusting 25 to 35 mph and minimum relative humidities dropping
  to around 30% or lower south of I-94.

- Cooler than normal temperatures are expected Sunday and Monday
  with highs remaining in the 30s. Wind chills in the single
  digits to around 0 degrees are likely Monday morning.

- Temperatures return to slightly above normal beginning Tuesday
  with the next chance for widespread measurable precipitation
  on Thursday.

&&

.DISCUSSION...
Issued at 220 PM CDT Fri Mar 15 2024

Tonight/Saturday:

Upper level shortwave trough and a leading sfc cold front set to
drop southeast out of Canada and push across the region tonight.
Some frontogenetic forcing with the boundary along with a streaking
50 kt 850 mb low level jet. Forcing suggests at least small rain
chances, but dry air currently in place along with saturation
concerns will work to limit those. Afternoon mixing continues to dry
out the near surface layer while short/medium range guidance holds
any "deeper" saturation across northeast Wisconsin. Stretching
southwest of there the moisture shallows out and may not be enough
to hold any pcpn chances. Locally, low end chances (10-20%) are
confined north/east of I-94. Minimal if any accums if realized.

More impacts will be the winds associated with the front/leading
edge of the shortwave. With the aforementioned low level jet a top
the system as it moves through and lack of a stronger sfc inversion
developing, mixing could/will still be realized. Gusts upwards of 30
to 35 mph are expected - roughly from midnight through 6 am.

The winds should settle down a bit for Sat morning before picking
back up Sat afternoon with mixing. However, saturation does increase
post the front, and promises some broken low/mid level cloudiness -
although trending north of I-90. Clouds will temper the mixing a bit
- but drying in the near sfc layer is again expected along with
winds gusts back into the upper 20s/lower 30s mph. With dry grasses
and other fuels, near critical fire weather conditions are expected.
More on that in the "Fire Weather" discussion below. Lastly, there
is a low end shot that there could be enough instability as cold air
a loft (+9 C 1000:850 mb lapse rates) suggests some convective
potential. Considering the dry air concerns (and likely more
drying), whether more than just some after CU would be realized is a
question. No meso/short term model support for even a smattering of
rain chances and will leave out of the forecast for now.

Sunday - Monday: Significantly Cooler

As we head into Sunday, an upper-level trough coming out of Canada
will usher in a cooler airmass with 850mb temperatures of -13 to
-15C in the deterministic 15.12z EC/GFS. Consequently, there is a
fairly good signal for temperatures to head below normal, the first
time for La Crosse and Rochester this month, with highs remaining in
the 30s areawide. Overnight Sunday and into Monday morning
temperatures will bottom out in the teens. With this in mind and
some increased northwesterly surface winds of 15-20 mph ahead of an
incoming high pressure center will allow for wind chills to tank
into the single digits, some spots even below zero.

With the Canadian airmass directly overhead on Monday, highs will
remain below normal with temperatures not escaping the 30s for most.
Monday generally will remain fairly clear with subsidence associated
with the aforementioned high pressure system keeping skies largely
void of cloud cover through Monday afternoon, especially further
south across northeast Iowa and southwestern Wisconsin.

Tuesday - Friday: Temperatures Rebound, Some Precipitation Chances

As the aforementioned trough and accompanied surface high pressure
departs the region, northwesterly surface flow will briefly turn to
southerly allowing for warmer air to be advected into the Upper
Midwest on overnight Monday and early Tuesday. This is ahead of a
weak surface low associated with a piece of vorticity caught in the
500mb northwesterly flow pattern. However confidence in any
meaningful precipitation is becoming lower as probabilistic guidance
in the 15.12z EC ensemble has lower confidence (30-50% chance)
for measurable precipitation with the 15.12z GEFS trending even
lower (10-20% chance) for Taylor County on Tuesday.

Otherwise, the main story for Tuesday and beyond will be the
recovering temperatures as highs will rebound above average once
again with highs across the region trending into the upper 40s to
lower 50s south of I-94 (lower to middle 40s north of I-94).
Expecting these highs to remain roughly steady-state through
Thursday with a quasi-zonal to northwesterly upper-level flow
pattern in place. Some uncertainty comes with a wave that approaches
regarding precipitation amounts and type but confidence is
increasing somewhat in measurable precipitation late week with
the 15.12z EC ensemble showing increased probabilities (60-80%
chance) for measurable precipitation.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 647 PM CDT Fri Mar 15 2024

VFR conditions will persist through Saturday with a period of
gusty WSW winds overnight tonight becoming NW on Saturday,
gusting 25 to 30 kts. Midlevel clouds will increase overnight
with lower 3.5-5kft VFR clouds moving in during the morning on
Saturday. A period of low level wind shear is possible for a
several hour window overnight tonight as winds aloft increase,
but with some mixing/gust potential, have not included mention
for now.

&&

.FIRE WEATHER...
Issued at 220 PM CDT Fri Mar 15 2024

Minimum relative humidity values will remain between 25 to 40
percent as forecast soundings show fairly prime mixing days into
next week. Saturday appears to be the main day of interest for fire
weather concerns with minimum relative humidities dropping as low as
the upper 20 percent range in spots. Certainly could see some
overachieving, cloud cover dependent, in relative humidities
with hydroplapse rates atop the mixed layer in the 15.16z RAP
suggesting dewpoints dropping from -12C to -37C in the 700-800mb
layer. This combined with increasing surface winds of 20 to 30
mph will allow for near-critical fire weather conditions during
the day Saturday. Areas of greatest concern will be along and
north of I-90 where minimal rainfall from earlier systems have
kept fuels dry. The one significant unknown for Saturday will be
how cloud cover trends will affect condtions during the
afternoon. Model soundings show a very shallow saturated layer
at around 4kft atop the mixed layer suggesting that low-level
cloud cover will be possible. The question remains if afternoon
mixing will help to clear this out which could allow our
relative hudmities to plummet. If cloud cover hangs does hang
around, this would keep our temperatures down and consequently
not allow our relative humidities to tank as effectively with
ineffecitve mixing.

Otherwise, as cooler temperatures move in for Sunday and Monday,
fire weather concerns mitigate some although relative humidities are
still expected to remain on the lower side with values forecast
between 25 to 40 percent through Wednesday. As a surface high
pressure system works its way south of the region, winds will
slightly begin to decrease with winds by Monday decreasing to 15-20
mph. May have to watch Tuesday for additional fire weather concerns
as temperatures begin to warm with clearer skies and increasing
winds.

&&

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

&&

$$

DISCUSSION...Naylor/Rieck
AVIATION...JM
FIRE WEATHER...Naylor


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.