Area Forecast Discussion
Issued by NWS La Crosse, WI

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143
FXUS63 KARX 180502
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1100 PM CST Wed Jan 17 2018

.SHORT TERM...(This evening through Thursday)
Issued at 230 PM CST Wed Jan 17 2018

At 2 PM, a tight southwest surface pressure gradient was bringing
slightly warmer air into the region from the Central Plains.
Temperatures ranged from the upper teens into mid-20s.

For tonight, a short wave ridge will build across the region.  This
will keep skies mainly clear.  This will allow a nocturnal inversion
to build across the area.  This inversion will be the strongest in
central Wisconsin where winds will fall to around 5 mph during the
overnight.  Due to this, lowered the temperatures a few degrees
lower than MOS.

On Thursday morning, a shortwave trough will move quickly southeast
across the northern Minnesota and northern Wisconsin.  With limited
moisture across the region.  Only expecting some clouds with its
passage.

With 925 mb temperatures around 3C warmer than this afternoon, the
high temperatures should easily climb into the lower and mid-30s on
Thursday afternoon.  This should allow the low water snow content to
compress even more.

.LONG TERM...(Thursday night through Wednesday)
Issued at 230 PM CST Wed Jan 17 2018

Highlights through this period include mild temps into the weekend
followed by a potential impactful system Sun/Mon.

The upper air pattern will continue to flatten late this week. On
Friday very mild 850 mb temps as high as 10-12C will overspread
the area ahead of a Pacific cold front sweeping through late
associated with a low pressure system passing well north across
Canada. These 850 mb temps correspond to NAEFS standard anomalies
of +2 to +3. With southerly winds becoming more southwesterly
ahead of the front, this set-up would support highs at least into
the low 40s in spots, depending on how thick any mid/high clouds
are along with influences from the snowcover. Behind the weak
front, little change in temps is expected, with well above average
highs on Saturday, albeit with more cloud cover than Friday.

The main period of interest remains the Sunday-Monday timeframe as
we continue to monitor a storm system expected to lift up towards
the area from the southwest.  17.12Z guidance indicates the upper
shortwave trough ejecting from the Rockies will be closed off
somewhere across the Midwest by Monday. Plenty of Gulf moisture
should be tapped with this system as strong northward low-level
moisture transport increases ahead of the low. There are still
considerable differences among model solutions with the placement
of the surface low track, impacting how much warm air is fed
northward into the area, and consequently precip types. The 17.12Z
deterministic models (EC/GFS/Canadian) showed a bit of a westward
shift with the surface low taking it up through Iowa and
Wisconsin Sunday night into Monday with perhaps some light mixed
precip Saturday night into Sunday and the bulk of the precip
holding off until later Sunday into Monday. However, given the
lack of consistency among solutions with placement/timing of the
low and still large envelope of possible solutions in the ensemble
guidance which would have significant impacts on precip types and
amounts, confidence in specifics remains low. While consensus
continues to increase that an impactful storm system will affect
the Upper Midwest during the later Sunday-Monday timeframe, it
remains too early to discern impacts to the local area.

Behind the system, not much in the way of cold air is expected, so
temps look to remain near seasonal averages into the middle of next
week. There could be a few upper waves impacting the area within
west to northwest flow, but nothing significant.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1100 PM CST Wed Jan 17 2018

Cigs/WX/vsby: an upper level disturbance will spin across northern
parts of the region on Thu, with the models holding any low cloud
threat northeast of the TAF sites. No wx/vsby impacts expected. VFR
conditions should hold through Friday.

Winds: tight pressure gradient will keep winds up overnight, holding
10+ kts through Thu afternoon. Some weakening in the gradient later
Thu night, with soundings suggesting decoupling at KLSE.

&&

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

$$

SHORT TERM...Boyne
LONG TERM...JM
AVIATION...Rieck



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