Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 230346
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1046 PM CDT Fri Mar 22 2024

.KEY MESSAGES...

- Potential winter storm continues for Sunday into early next
  week. This storm will bring snow, then rain to the region.
  Winds are forecast to gust 30 to 40 mph which would lead to
  some blowing and drifting, however with the warming
  temperatures and snow changing to rain. A winter storm watch
  may be needed for parts of southwest Minnesota and west
  central Wisconsin.

&&

.DISCUSSION...
Issued at 300 PM CDT Fri Mar 22 2024

Tonight through Saturday...

High pressure will build across the Upper Mississippi River Valley
tonight. As this occurs, skies will gradually clear this evening.
Mid and high clouds will gradually increase on Saturday as warm air
advection increases ahead of a shortwave trough ejecting northeast
out of the Central Plains. A few of the CAMs even suggests that some
light snow may move into northeast Iowa and southeast Minnesota
during the late afternoon. However, soundings suggest that this
initial band of snow may be fighting low level dry air, so it might
end up being mainly virga. Low temperatures tonight range from 10 to
20. High temperatures on Saturday will be in the 30s.

Active weekend weather into early next week:

Attention now turns to the weekend storm system into next week.  The
pattern has the heights breaking down across the region
Saturday night as a broad 500mb trough over the western U.S.
begins to move into the Rockies. Meanwhile surface low pressure
begins organizing in the lee of the Rockies around 985mb. This
fairly disorganized broad area of low pressure appear to
develop a closed mid-tropospheric low over the Plains Sunday
night. The low opens up and becomes negatively tilted as it
heads toward the Upper Mississippi Valley Monday into Monday
night. It appears to slow as the trailing trough phases with it
and tries to consolidate over parts of southern Canada and the
Dakotas through Tuesday. The surface low moves into the Plains
Sunday night, working toward the Missouri River Valley by
25.12-18Z the southern Minnesota/central Iowa by 26.06Z Monday
night, lifting north from near KRST toward Duluth through 18Z
Tuesday.

Operational models have very good synoptic model to model
consistency through Sunday morning. Beyond this time, the models
have good general consistency, but differ on the the strength of the
mid-level waves and the finer details in the track and qpf. These
details will pay a role in the temperature profiles, precipitation
type, and how much precipitation will fall.  The current WSSI-P
(probabilistic WSSI) shows the highest confidence in "Moderate"
winter impacts west if I35 in Minnesota into the Dakotas and parts
of Iowa and Nebraska.

Precipitation type, amounts, temperatures, and winds:

Saturday night and Sunday, as low pressure deepens to 978 to 982mb,
a low level jet is forecast to develop and strengthen 40 to
50kts across Iowa and southern Minnesota. Multiple rounds of
warm air advection combined with the track of the upper level
trough/vorticity advection, the broad upper level support being
in the right rear entrance region of the jet,the low level jet,
and strong moisture transport results in multiple rounds of
precipitation. The more widespread precipitation; especially
Sunday into Monday morning. The exact precipitation type will
depend on the track and thermal profiles. For now, the snow
accumulations ramp up Sunday afternoon and Sunday night and
taper off north of I94 as the warm air moves in and the
precipitation changes to rain. Southeast winds increase Sunday
30 to 40mph and continue Sunday night. This will result in some
blowing/drifting snow. As temperatures warm and the rain fall on
the snow the winds will become less of a factor. The resultant
snow totals based on the current track, temperatures, and QPF,
have the most impactful area west of a line from St. Ansgar
toward Preston to north of La Crosse and Sparta with 3"+ and 6"+
could fall west and north of a line from Rochester toward Black
River Falls. A winter storm watch may be needed due to the snow
and winds.

Instability aloft arrives Monday (possibly 50-250 J/kg), thus could
see some thunderstorms.  Prelim forecast soundings show skinny CAPE,
and potential for deep layer shear of 40 to 55kts.

The 22.00Z EFI shows that 70 to 90% of the EC members have
anomalous snow/QPF Sun-Mon across parts of the region. For
Sunday, the higher values remain to our west. For Monday, these
value increase as you head toward Rochester and Minneapolis.
The shift of tails of 1 to 2 for snow is no longer in our local
area.

At this time the bulk of the precipitation appears to end before
the cold air wraps back into on the backside, but we will
continue to look through all these details in the coming shift.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1046 PM CDT Fri Mar 22 2024

Skies continue to clear from north to south as cold front continues
southward drift. VFR conditions expected well into Saturday and
winds continue to diminish as well.

Good aviation weather expected through the day Saturday but as
clouds advect in ahead of larger system by Saturday night, expect
VFR ceilings to develop with lowering ceilings going into the
overnight Sunday morning. Could even see some MVFR ceilings develop
with light snow returns late in forecast period, while bulk of
precipitation expected after.

&&

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

&&

$$

DISCUSSION...Boyne/Zapotocny
AVIATION...Shea


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