Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 242329
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
629 PM CDT Sun Mar 24 2024

.KEY MESSAGES...

- An impactful winter storm expected to affect the area into
  Tonight.

- Monday and Monday Night will be warmer with periodic rain
  showers.

- Colder air will move into the region on Tuesday. Rain will
  change over to snow. Little snow accumulations expected.

&&

.UPDATE...
Issued at 455 PM CDT Sun Mar 24 2024

At 2145z, KARX reflectivity depicts a very impressive 40-50dbz band
of precipitation moving through northeast Iowa quickly to the
north. As it approaches, heavy snow with very large dendritic
flakes have been noted on IA plowcams and by observers at onset
of heavy precipitation. The thermodynamics within this band of
precipitation are very complex with KARX correlation coefficient
at this time showing a profound melting layer working in from
the south associated with strong mid-level warm air advection
with a 700-900mb jet approaching upwards of 60 kts in recent RAP
soundings at KDEH. Consequently, this has enabled a stronger
forcing regime allowing for very heavy precipitation rates (even
a couple of lightning flashes noted as well!) within this band
albeit some of it may be slightly overexaggerated by radar due
to melting layer contamination. As the band progresses through,
strong warm air advection aloft will allow for precipitation to
switch over from snow to rain as noted in several observations
across northeast Iowa, with a period of heavy sleet being
possible in spots. Heavy snow within the band could produce
rates of 1-2" per hour leading to quick slushy accumulations on
roadways. As a result, deciding to hold onto the Winter Weather
Advisory south of I-90 in northeast Iowa for now.

&&

.DISCUSSION...
Issued at 122 PM CDT Sun Mar 24 2024

Tonight - Snow changing to rain

The warm front will lift northward across the northern half of the
forecast area. The combination of 850 mb moisture transport and
isentropic lift will result in a snow band lifting northward across
the area. The 24.12z HREF continues to show that the hourly snow
rates in this band will likely (50-80 percent probabilities) exceed
1 inch per hour. These higher snow rates will likely over any given
area for up to a 2-hour period. As far as snow totals, they look
rather similar to the ones that we sent out yesterday. The only
changes were to north-central Wisconsin where the ranges look to be
coming in on the lower end of guidance.

The meso models and CAMS are in fairly good agreement that the
850 mb 0C isotherm will near the Interstate 90 around 25.01z,
Interstate 94 around 25.04z, and in Taylor County around 25.07z.
As this warmer air aloft moves northward the snow will
transition to rain.

Another shortwave trough will move northeast across the area during
overnight. This narrow band of precipitation will be in the form of
rain. Additional rain totals will be up to a tenth of an inch.
Depending on surface temperatures overnight, there may be some light
icing in north-central Wisconsin.

Monday and Monday Night - Scattered rain showers

A combination of 850 mb moisture transport and a series of weak
shortwaves moving northward will provide periodic showers. The
24.12z HREF 24-hour QPF ensemble mean is anywhere from a 0.25
and 0.75 inches, 0.5 to 1 inch for southeast Minnesota and
southwest and central Wisconsin, and between 1 and 1.5 inches
for Clark and Taylor counties in north-central Wisconsin.

With more showers expected, the high temperatures are slightly
cooler for Monday south of Interstate 94 with highs in the lower and
mid-50s. Meanwhile, there was very little chance for the rest of
the area with highs in the mid and- upper 40s.

Tuesday - Rain changing back to snow with little accumulations
expected

On Tuesday morning, a cold front will move east through the area.
Strong cold air advection it`s wake will cause temperatures to
slowly fall throughout the day. As this occurs, the wrap-around
moisture will gradually change over to snow. With this occurring
about 6 to 12-hours later than it looked yesterday, snow amounts
look to be anywhere from a dusting to a half-inch.

Tuesday Night into Wednesday - May be some scattered snow
showers in north-central Wisconsin

A 500 mb trough will remain across the Great Lakes. The combination
of cyclonic flow and low level moisture will keep skies mostly
cloudy north of Interstate 94. There may be just enough moisture in
Taylor County (north-central Wisconsin) for a maybe a few snow
showers. Confidence was not high enough to include these in the
forecast at this time.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 629 PM CDT Sun Mar 24 2024

With such dynamic and changing weather as large storm system impacts
region next couple days, wide variety of flight categories. Bands of
snow moving through the region with IFR to LIFR ceilings being
quickly replaced with liquid precipitation and improving ceilings
from the south. But questions on how much improvement we will see
the further west and north you go where at least IFR conditions
could continue, especially as snow falls.

More showery regime with convection should allow for periods of
improvement, especially on Monday but this will be difficult to time
outside of 2-4 hours in advance.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning until 1 AM CDT Monday for WIZ032>034.
     Winter Weather Advisory until 10 PM CDT this evening for
     WIZ041>044-053.
     Winter Storm Warning until 10 AM CDT Monday for WIZ017-029.
MN...Winter Weather Advisory until 10 PM CDT this evening for
     MNZ086>088-094>096.
     Winter Storm Warning until 1 AM CDT Monday for MNZ079.

IA...None.

&&

$$

UPDATE...Naylor
DISCUSSION...Boyne
AVIATION...Shea


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