Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 251658

Area Forecast Discussion
National Weather Service La Crosse WI
1158 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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1158 AM CDT Tue Apr 25 2017

Conditions expected to deteriorate over the next 24 hours as low
pressure moves out of the Plains into our region. Currently
watching a band of scattered shra on radar in advance of this low
moving into northeast IA/southern MN. Most of this was falling
out of higher/VFR cloud base so some of it was evaporating before
hitting the ground per surface observations under the radar echo.
More widespread shra activity expected to overtake the area
tonight through Wednesday as the low moves over the region. Plan
on MVFR cloud moving into KRST after 02z, lowering further into
LIFR after midnight. KLSE expected to stay VFR this evening,
lowering into MVFR after 06z.




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