Area Forecast Discussion
Issued by NWS La Crosse, WI

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471
FXUS63 KARX 250817
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
317 AM CDT Tue Apr 25 2017

.SHORT TERM...(Today through Thursday)
Issued at 317 AM CDT Tue Apr 25 2017

The cold front this morning was located across south central
Minnesota southwestward into the central plains. Ahead of the
front, temps have remained mild overnight with southerly flow.
However, the air mass remains very dry, with deeper moisture still
confined well south.

Northward moisture transport will finally get going today ahead of a
strong shortwave ejecting from the Desert Southwest. The cold front
will be slow to make much eastward progress until the upper
trough begins to lift northeastward. As a result, one more mild
day is expected with highs in the 60s and low 70s and lighter
south winds. A weak lead shortwave along with increasing moisture
transport should result in a band of showers lifting north this
afternoon. However, the more widespread precip will remain mostly
post-frontal today, so much of the day today may be dry.

By tonight and Wednesday the front begins to move east, bisecting
the area by Wednesday morning. Large scale forcing will increase as
upper level shortwave energy lifts through the area ahead of the
approach of the upper trough leading to increasing coverage of
showers tonight. A few hundred J/kg MUCAPE later tonight could
result in a rumble of thunder, but instability does remain weak. The
front will move east of the region by late Wednesday. The 25.00Z
GFS/ECMWF are slightly farther east with the upper trough by Wed
night/early Thursday compared with the NAM, and thus move much of
the rain east by Wed night. The NAM keeps a stronger deformation
precip band across the region during this time with temps cool
enough for some wintry precip on the western edge. For now have
trended towards consensus, keeping mainly rain chances.

Deeper moisture will eventually make it into the region, with
precipitable water values rising to around 1.25 inches Wed
morning. Barring any localized convection, it looks like rainfall
with this system will not be excessive, though some 1"+ totals
are possible. The heaviest deformation zone precip is expected to
be from south central MN northeastward into northern Wisconsin
later today into Wednesday while convection ahead of the front
associated with increasing moisture transport and a developing
low level jet ahead of the upper trough later Wed/Wed night appear
to be focused mainly east of the area. Thus, much of the area may
avoid the heaviest rain with this system.

Much cooler air works in behind the system on Thursday with high temps
confined to the 40s to near 50. Cyclonic flow around the upper
low progressing slowly around the US/Canada border will keep
clouds around and possibly some showers.

.LONG TERM...(Thursday night through Monday)
Issued at 317 AM CDT Tue Apr 25 2017

A cool but active pattern will continue through the weekend. The
GFS/ECMWF differ on the placement of a lead upper wave on Friday
ahead of an amplifying trough across the southwest CONUS. The
farther north GFS would bring precip chances north on Friday while
the farther south ECMWF would suggest dry weather on Friday.

However, during the weekend, the upper trough is expected to lift
northeastward towards the Great Lakes with a surface low lifting
into the Midwest. This will lead to increasing precip chances
later Saturday and Sunday, possibly lingering into Monday. Below
average temps will persist through early next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1152 PM CDT Mon Apr 24 2017

A cold front extended from central Minnesota into eastern Nebraska
late this evening. This front will continue to move slowly east
through Tuesday evening and is expected to reach western Wisconsin
and eastern Iowa. Moisture will continue to return to the region
ahead of the cold front which will allow for the ceilings to
gradually come down during the day Tuesday, but should remain VFR.
The 24.00Z NAM and the meso-scale models continue to show almost
all the rain remaining behind the front Tuesday closer to the
upper level low and short wave trough that will be back across the
Dakotas. The exception to the this looks to be a wing of showers
that works from south to north across the area from late morning
into the middle of the afternoon that could bring a couple hours
of rain to KRST. As the upper level low and short wave trough
catch up with the front Tuesday evening, the showers should then
become more widespread and start to move out ahead of the front as
well. As this occurs, the ceilings should go down to MVFR for both
airports with some reductions to the visibility also possible.


&&

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

$$

SHORT TERM...JM
LONG TERM...JM
AVIATION...04



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