Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 181656
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1056 AM CST Tue Feb 18 2020

.SHORT TERM...(Today and tonight)
Issued at 212 AM CST Tue Feb 18 2020

As the surface low retreats into Lower Michigan early this morning,
lingering snow is gradually coming to an end across western
Wisconsin. Expect it to exit our eastern counties by about 4-5am
with less than a half inch of additional accumulation. A respectable
pressure gradient is developing on the back side of this departing
system, with brisk northwest winds gusting to around 20-30 mph. Cold
air advection will ramp up early this morning with temperatures
quickly dropping from the 20s/30s into the teens/20s through
daybreak. A clearing slot moving into southeast MN will also
contribute to the cooling cause, and forecast soundings show the
column quickly drying by daybreak as drier air filters into the
region. Indeed, a swath of clouds upstream from the clear slot over
western/northern MN is showing signs of eroding, so some areas will
manage to see some sunshine today. Highs this afternoon will range
from the teens to the 20s.

Colder air will spill into the region tonight as Canadian high
pressure settles over the Dakotas. Cold air advection will slowly
lose its momentum as northwest winds gradually relax across the
region. With clearing skies, lows will tumble below zero across much
of the area, ranging from near -10 in the far north to +5 in the far
south.

.LONG TERM...(Wednesday through Monday)
Issued at 212 AM CST Tue Feb 18 2020

Strong surface high pressure will continue to strengthen to about
1048mb as it slides from the Dakotas on Wednesday toward the
Minnesota/Iowa border by Thursday morning. This surface high will
strengthen to around +3 standard deviations above the mean.
Resultant deep subsidence in conjunction with a progressively drier
airmass filtering into the region (PWATs <0.1") will favor a
prolonged dry stretch for the forecast area. Should be noted,
though, that models are in good agreement with some snow showers
developing nearby over western/central Iowa on Wednesday in response
to some frontogenetic forcing. If that fgen axis would progress any
further east, may need to introduce a slight chance of snow showers
for northeast Iowa.

Arctic air will spill into the region on Wednesday with that
Canadian high, causing 925/850mb temps to plummet to around -16 to
-18C at LSE. This isn`t too anomalous for late February, roughly 2
standard deviations below the mean and certainly not as cold as late
last week. Nevertheless, Wednesday`s highs will be in the single
digits/teens, and Wednesday night will be frigid with lows well
below zero for most. Winds will be light with the center of the high
sitting over the MN/IA border, but even light winds at those
temperatures may produce wind chills briefly near advisory
thresholds in some areas. Something to monitor, but as of now looks
rather marginal for an advisory.

As the high slides by to our south on Thursday, the cold air aloft
will retreat off to the east and surface winds will swing around to
the southwest. Modest warm air advection will develop across the
Upper Mississippi Valley, continuing through Friday night.
Temperatures will be slow to respond at first with highs Thursday
just a couple degrees warmer than Wednesday and lows Thursday night
still within a few degrees of either side of zero. By Friday,
though, highs will jump into the upper 20s to low 30s with some 40s
likely over the weekend.

Dry weather looks to continue into the weekend. A cold front and mid-
level wave are progged to cross the area Saturday night, but
deterministic guidance suggests a rather dry airmass still overhead.
A few GEFS members paint some light precip over the region late in
the weekend, but am skeptical of those solutions given the lingering
dryness. Our precipitation-free stretch may well continue into early
next week per latest guidance.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1057 AM CST Tue Feb 18 2020

Generally VFR conditions will continue into Wednesday. However,
upstream obs indicate SCT-BKN MVFR stratus through central MN in
the vicinity of a secondary cold front dropping southeast. A
several hour period of MVFR ceilings is possible late this
afternoon/evening, with the higher chances at KRST. Otherwise, NW
winds will continue, gusting occasionally up to 20 kts today.

&&

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

$$

SHORT TERM...Kurz
LONG TERM...Kurz
AVIATION...JM



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