Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 212318
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
518 PM CST Tue Nov 21 2017

.SHORT TERM...(Tonight through Wednesday)
Issued at 215 PM CST Tue Nov 21 2017

Relatively weak upper level shortwave trough slated to drop
southeast across the northern plains and into IA by 12z Wed. RH
lacking at the outset, with the models further drying it out as it
approaches the local area. Perhaps a few high clouds, otherwise no
impact.

Another shortwave trough, a bit perkier, will spin southeast across
MN/WI Wed night. Pretty good shot of 850-700 mb QG convergence and
850 mb warming sweeps over the local area during the evening.
Moisture continues to be an issue with this shortwave though, and
will be a limiting factor to pcpn chances. RH fields and north-south
running x-sections point to holding the deeper saturation across the
north. Meanwhile, Bufkit soundings also show a sizable dry layer
under the anticipated cloud bases. Any pcpn that could/would get
produced would have to battle that to reach the surface. Going to
hold small chances across the far north for now, and keep an eye on
the south. May add a few flurries in. x-sections and soundings
suggest there would be enough ice in the cloud for ptype to be snow,
but hints on the start/end of chances that loss of ice in cloud
could be an issue. Expect any amounts to be minimal, but it bears
watching.

.LONG TERM...(Thanksgiving through Tuesday)
Issued at 215 PM CST Tue Nov 21 2017

GFS and EC continue to mimic each other for the long Thanksgiving
weekend. Front end still looking seasonable to mild as shortwave
upper level ridge works across the region and the sfc flow turns
southerly. 850 mb temps still progged to climb to +10C or so by 18z
Friday...a 20 degree climb from this afternoon. EC continues to be
the warmer of the two, suggesting a few locations could near 60
Friday. Some questions remain though on the passage of a cold front
and associated clouds, especially for northern parts of the forecast
area. Will stick with consensus temps for now.

Speaking of the cold front, the boundary will lead its parent upper
level shortwave trough Fri afternoon/evening. Some low level
moisture transport ahead of the front into the region, but most of
the saturation is post the front-where the shortwave can work on it
(although deepest still lies well north of the local area). Models
continue to lay their best qpf potential across northern parts of MN
and WI Friday, but bring lighter amounts down to 1-90 and a bit
south of there. Consistent signal the past couple days. Temperatures
will be warm enough to keep ptype as rain.

Another slug of cold air drops southward from Canada post the cold
front with 850 mb temps back to -8C by 18z Sat. The cold air settles
in for the weekend, but in this progressive upper level flow
pattern, moves quickly out for the start of the new work week. Highs
in the 30s Sat/Sun should moderate back into the 40s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 518 PM CST Tue Nov 21 2017

VFR conditions expected the next 24 hours as high pressure works
through the region, with northwest winds gradually subsiding
through the night before switching southerly in the 8-14 knot
range later Wednesday. We should also see a rapid increase in mid
level clouds Wednesday afternoon, with perhaps a stray flurry at
LSE or RST. However, the greater risk for some light snow will
be noted well north of those sites, up toward central Wisconsin.

&&

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Lawrence



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