NWS-La Crosse Forecast Discussion

						FXUS63 KARX 191035
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
535 AM CDT Wed Mar 19 2025

.KEY MESSAGES...

- An impactful winter/spring storm will move through the Upper
  Mississippi River Valley today and tonight bringing a narrow
  band of heavy snow, strong winds, and isolated to scattered
  morning storms.

- Isolated to scattered storms in southwest Wisconsin, and parts
  of northeast Iowa and southeast Minnesota this morning. A few
  of these storms may produce small hail.

- The band of heavy snow (4 to 8 inches - locally higher) was
  shifted southeast. At this time, the heaviest snow looks to
  fall from Mason City, IA northeast to Wausau, WI.

- Strong north winds (sustained winds of 25 to 40 mph and wind
  gusts of 40 to 55 mph) from this afternoon into the evening.
  These strong winds will likely produce white-outs and blizzard
  conditions. In addition, there could be some power outages.

&&

.DISCUSSION...
Issued at 327 AM CDT Wed Mar 19 2025

Through Tonight

The deepening low pressure area will move across southern and
eastern Iowa this morning. A coupled 250 mb jet will be located
across the region this morning and then shift east of the area
this afternoon. This will enhance the upper level divergence
across the region. In addition, up to 500 J/kg most-unstable
CAPES will move into southwest Wisconsin, and parts of southeast
Minnesota and northeast Iowa. This will result in isolated to
scattered storms. With cold air aloft and elevated skinny CAPE,
a few of these storms may produce some small hail.

The 19.00z models shifted the heavy snow band slightly
southeast Mason City, IA to Wausau, WI. The models continue to
show that this band will likely produce hourly snow rates of 1
to 2 inches this afternoon. Snow totals still look to be in the
4 to 8 inch range. The 19.00z SPC HREF 24-hour ensemble
probability-matched mean still has a narrow (1 county-wide)
band of 10 to 15 inches. Due to strong north winds (strongest
this afternoon and evening), the wet-nature (wetter than the
typical 13 to 1 ratio which will result in more compaction) of
this snow, and short-duration (6 to 8 hours), there is plenty
of uncertainties on whether these higher snow will actually be
observed. With the snow band shifting southeast, we decided to
add a few more counties to the Winter Weather Advisory
(Chickasaw, Allamakee, Vernon, Adams, and Juneau counties) and
Blizzard Warning (Floyd and Howard counties). With the blowing
and drifting snow expected to continue into this evening, the
ending time was pushed back from 20.00z to 20.03z.

The combination of a tight surface pressure gradient and steep
surface to 875 mb lapse rates, surface winds will range from 25
to 40 mph and wind gusts will range from 40 to 55 mph. The
strongest winds will be from this afternoon into this evening.
The winds will gradually shift from northeast to north this
morning and then continue out of the north through this evening,
and gradually subside and shift to the northwest overnight.
These strong winds will likely produce white-outs and blizzard
conditions. In addition, there could be some power outages.

Friday and Friday Night

Another 500 mb shortwave trough will move southeast through the
area. Unlike its predecessor, this system is initially moisture
starved. As a result, much of the initial lift goes toward
saturation. As far as the probabilities of at least 0.05 inches of
QPF, the grand ensemble has up to a 15 percent north of Interstate
90 and 15 to 30 percent for the remainder of the area. Boundary
layer temperatures continue to support that this precipitation will
be mainly rain. High temperatures on Friday will range from the mid-
40s to mid-50s.

Late Saturday Night into Monday

The models show that an open 500 mb short wave will southeast into
the area on Sunday. This system then deepens and closes off to form
a 500 mb low. There continues to be some uncertainty on how
progressive this system will be at moving out of the Great Lakes
early in the week. This impacts how long the precipitation will
remain across the Upper Mississippi River Valley and how fast the
western CONUS ridge builds eastward across the region (this will
impact temperatures). There continues to be quite a bit of spread in
the Grand Ensemble on QPF amounts. The 10th percentile ranges from a
trace to a few hundredths of an inch. Meanwhile, the 90th percentile
ranges from a half of an inch to 0.65 inches. In addition,
precipitation type remains uncertain. The NBM 10th percentile would
keep the high temperatures on Sunday and Monday in the 30s.
Meanwhile, the NBM 90th percentile would have high temperatures
ranging from the mid-40s to near 60 on these days.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 536 AM CDT Wed Mar 19 2025

Currently watching some convection moving through southern Iowa.
If these storms hold together, they would impact KLSE around
19.14z. Snow will move into KRST around 19.14z and then persist
through 20.02z. Delayed the onset of the blowing snow until the
early afternoon. With no snow on the ground, we will have to
wait until there is about 2 inches on the ground for this snow
to become airborne again. As far as KLSE, the precipitation will
start out as rain and than transition to snow around noon. North
winds will increase into the 20 to 35 knot range with gusts of
35 to 50 knots this afternoon and then continue into this
evening. Snow totals will likely range from 4 to 8 inches for
KRST and 2 to 4 inches for KLSE.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from noon today to 10 PM CDT this
     evening for WIZ041>044-053.
     Wind Advisory from 1 PM this afternoon to 7 AM CDT Thursday
     for WIZ054-055-061.
     Winter Storm Warning until 10 PM CDT this evening for WIZ017-
     029-032>034.
MN...Blizzard Warning until 10 PM CDT this evening for MNZ079-086-
     087-094-095.
     Winter Weather Advisory from noon today to 10 PM CDT this
     evening for MNZ096.
     Winter Storm Warning until 10 PM CDT this evening for MNZ088.
IA...Blizzard Warning until 10 PM CDT this evening for IAZ008-009-
     018.
     Winter Weather Advisory from noon today to 10 PM CDT this
     evening for IAZ010-011-019.
     Wind Advisory from 1 PM this afternoon to 7 AM CDT Thursday
     for IAZ029-030.

&&

$$

UPDATE...Zapotocny
DISCUSSION...Boyne
AVIATION...Boyne