Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 190829

Area Forecast Discussion
National Weather Service La Crosse WI
329 AM CDT Tue Sep 19 2017

.SHORT TERM...(Today and tonight)
Issued at 324 AM CDT Tue Sep 19 2017

At 3 AM, weak 850 mb moisture convergence associated with the low
level jet is resulting in scattered showers along north of the
Interstate 94 corridor in Wisconsin. The 19.00z models are in very
good agreement that this moisture transport will gradually wane
during the remainder of the overnight. As a result, expect these
showers will be gone by day break.

The models are in good agreement that the clouds will gradually
dissipate this morning and that the afternoon will be partly to
mostly sunny. High temperatures will range from the mid 70s to
lower 80s.

For tonight, the 850 mb moisture transport will increase
dramatically ahead of an approaching longwave trough. In addition,
the mixed layer CAPES will climb into the 1000 to 1500 J/kg across
southeast Minnesota and northeast Iowa. A squall line will develop
over the eastern Dakotas and western Minnesota during the evening
and this will march toward our area during the overnight. As the
main short wave energy ahead of this trough ejects into northern
Minnesota, this line will slow and weaken as it moves east across
eastern Minnesota and northeast Iowa.

.LONG TERM...(Wednesday through Monday)
Issued at 324 AM CDT Tue Sep 19 2017

On Wednesday, a cold front will push east across the Upper
Mississippi River Valley. By noon, this front will be close to
the Mississippi River and it will east of the area by 00z
Thursday. Despite the short wave moving northeast into Canada,
there will be sufficient shear and instability for supercells to
develop ahead of the cold front. The main severe weather threats
would be damaging winds and large hail. However, with this said,
it may be east of our area before this occurs.

On Thursday, the GFS and GEM produce showers and storms south of
the Interstate 90 corridor. Meanwhile, the NAM and ECMWF are dry.
Looking at the soundings for this time period, the atmosphere
looks too capped for any precipitation to form. Due to this,
removed the precipitation for this time period.

From Friday into the weekend, the upper level ridge will be
building across the region. This will slow the eastward progress
of a cold front over the northern and central Plains. Due to this,
confined the rain chances to north-central Wisconsin and southeast
Minnesota. I would not be surprised that even these areas could
be potentially dry too. Southwest flow ahead of this cold front
will likely result in warmer temperatures than the MOS guidance.
As a result, the temperatures were raised anywhere from 3 to 5F.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1138 PM CDT Mon Sep 18 2017

A few showers continue to percolate very late this evening, but
should largely not impact RST or LSE the remainder of the night.
Instead, lower stratus continues to push across the area, but is
showing signs of thinning. Where clouds thin, fog is likely to
develop, especially at RST where a period of VLIFR conditions is
possible. LSE remains more problematic as confidence in clearing
isn`t the highest. For now, will maintain a lack of any fog
mention but watch trends closely the next few hours. Any
fog/stratus will lift and thin through the morning hours, with
winds from the southeast increasing at 10-15 knots, with some
gusts to 20 knots likely during the afternoon. Stronger flow will
then continue into tonight, with just a very low end risk for a
shower or thunderstorm, mainly toward or just after 06Z.




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