Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 040910

Area Forecast Discussion
National Weather Service La Crosse WI
310 AM CST Mon Dec 4 2017

.SHORT TERM...(Today and tonight)
Issued at 310 AM CST Mon Dec 4 2017

Water vapor imagery early today indicated an upper trough ejecting
across the central Rockies. Surface analysis indicated the
associated surface low across central South Dakota with a warm
front lifting northward across southern Minnesota into central
Wisconsin. Broad low to mid-level warm advection was occurring
ahead of the surface low across the Upper Midwest with strong low-
level moisture transport into the Upper Mississippi Valley aided
by a 50-60 kt 850 mb jet. Showers increased rapidly within this
regime on the nose of the stronger moisture transport with some
thunder as well given up to around 500 J/kt of MUCAPE. Expect the
most widespread shower activity to lift northeast early this
morning coincident with strongest warm advection/moisture
transport signal. After that, coverage of precip should fall off
with broader weak forcing and mid-level drying. Will have to watch
for the potential for a line of showers or low-topped storms to
form later in the afternoon along the cold front as it sweeps
eastward, especially across western Wisconsin. Otherwise, expect
one more very mild day before the marked change to colder temps.
Early morning temps were up into the mid 50s in spots already,
some 20 degrees above average highs. Cloud cover and precip will
keep temps from warming dramatically, but 50s to low 60s are
likely, nearing record highs at some sites.

Strong low-level cold advection will quickly develop behind the cold
front late today and this evening. Lapse rates will steepen with
mixing up to 850 mb where wind speeds may approach 50 kts for a
time this evening. Expect strong gusty winds tonight given this
set-up. Will go ahead and add the remaining counties east of the
Mississippi to the Wind Advisory beginning at 00Z and ran the
advisory through 10Z Tuesday west of the Mississippi and 12Z to
the east. Still looks like the portions of southeast Minnesota
into north-central Wisconsin may be grazed by the deformation
precip band tonight, but with little accumulation.

.LONG TERM...(Tuesday through Sunday)
Issued at 310 AM CST Mon Dec 4 2017

Tuesday will have a markedly different feel from today with temps
some 30 degrees colder. Little rise in temperature is expected
with gusty west winds that could near advisory levels again. Wind
chills will hover in the single digits and teens through the day.
Some light snow/flurries will remain possible, especially over
northern Wisconsin.

There`s good agreement in the general pattern evolution through the
week into the weekend with a cold northwest flow pattern across the
area in between an amplified western CONUS ridge and the eastern
trough. As a result, do not expect much day-to-day change in
temps through late week, with highs generally remaining in the 20s
and lows in the single digits and teens. All in all, not a lot of
precip is expected during this time with embedded systems having
little moisture to work with. However, any shortwave rippling
through the flow could generate some light snow/flurries. The best
signal for light snow continues to be on Thursday night and
Friday as both the GFS/ECMWF indicate a stronger upper wave
sinking southward across the Upper Midwest.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1125 PM CST Sun Dec 3 2017

Multiple challenges persist over the next 24 hours at both TAF
airfields as a strong low pressure system moves across the
region. These include timing of lower ceilings/rain and timing/
magnitude of low-level wind shear.

VFR ceilings for most of last evening will eventually give way to
MVFR/IFR cloud bases overnight as low-levels saturate. With these
lower clouds will come a chance for rain and some reductions in
visibility to around 5 SM. Could even see a few thunderstorms,
especially at KLSE, but not enough confidence to add at this time.
A dry slot will then move into the area Monday afternoon,
bringing an end to the rain and higher cloud bases. While VFR
conditions should continue through the rest of the period at KLSE,
a return to MVFR ceilings is likely at KRST as a deformation
precipitation band passes to the north and west.

Southerly winds will be strong through Monday afternoon with
frequent gusts between 20 and 30 kts. Winds then shift quickly to
the west Monday evening as a cold front passes through the area.
Gusts behind the front are likely to increase to between 30 and 40
kts, possibly higher at KRST. For tonight, still expecting low-
level wind shear issues with 45 to 50 kts in the 1500 to 2000 ft
agl layer, but these concerns will wane Monday morning as surface
winds increase.


WI...Wind Advisory from 6 PM this evening to 6 AM CST Tuesday for

MN...Wind Advisory from 3 PM this afternoon to 4 AM CST Tuesday for

IA...Wind Advisory from 3 PM this afternoon to 4 AM CST Tuesday for



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