Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 212042

Area Forecast Discussion
National Weather Service La Crosse WI
342 PM CDT Wed Mar 21 2018

.SHORT TERM...(This evening through Thursday)
Issued at 340 PM CDT Wed Mar 21 2018

At 3 PM, a 1016 mb high was located over southern Wisconsin. This
high was producing mostly sunny skies across southern Wisconsin
and Illinois. Meanwhile, a shortwave over central Minnesota was
producing clouds mainly west of the Mississippi River. With the
airmass very dry across the region, only expecting clouds as it
moves through the Upper Mississippi River Valley. Low temperatures
tonight will be in mid teens in central Wisconsin and in the 20s
across the remainder of the area.

On Thursday, high pressure will provide partly to most sunny
skies. High temperatures will range from the lower 40s to lower

.LONG TERM...(Thursday night through Wednesday)
Issued at 340 PM CDT Wed Mar 21 2018

From Friday afternoon into Saturday morning, the 21.12z models
continue to show that a low pressure system will move from Kansas
to southern Illinois. A strong band of 800 to 500 mb
frontogenesis will develop north of the this low across southern
Minnesota, Iowa, northern Illinois, and far southern Wisconsin.
This system continues to show that it will draw Gulf of Mexico
moisture northward into the region. Precipitable water values will
climb into the 0.50 to 0.75 inch range across parts of southwest
Wisconsin, northeast Iowa, and southeast Minnesota. Meanwhile, the
cold conveyor belt will bring dry Canadian air into central,
west-central, and north-central Wisconsin. All of this will result
in a narrow (2 to 4 county wide) heavy snow band. The main
question is where this band will ultimately end up. There are some
indications that there will be the potential of some slantwise
convection which could enhance the snow rates. The SPC SREF shows
a 30 to 50 percent chance of hourly snow rates of over 1 inch per
hour across southeast Minnesota, northeast Iowa, and parts of
southwest Wisconsin. With both the 21.12z GEFS and 21.15z NCEP
SREF precipitation and snow accumulation plumes continuing to
show a wide variety of solutions which are evenly distributed. As
a result, confidence was not quite high enough to issue a Winter
Storm Watch at this time. In addition, there is also some
uncertainty on when the snow will end across the area. Both the
GFS and NAM quickly bring dry air into the region on Saturday
morning as the surface low moves into the Tennessee River Valley.
Meanwhile, the ECMWF lingers an inverted trough over the area and
this keeps into snowing into the early afternoon.

In the wake of this system, the flow aloft will become southwest.
The models are continuing to show that a series of low pressure
system will eject out of the western longwave trough and move
through the region early next week. With the timing and location
of these waves uncertain, made little change to the blended grids.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1244 PM CDT Wed Mar 21 2018

Main taf concerns are location of MVFR/VFR condition/
stratocumulus deck of clouds...which are currently over much of
Minnesota. Latest metars show clouds are MVFR over central
Minnesota and VFR elsewhere. Latest 21.12z deterministic models
suggest MVFR conditions will remain west of both RST/LSE taf sites
through the period. This is based on dry easterly flow near the
surface allowing for some erosion on the eastern periphery of the
stratocumulus deck. Confidence remains high VFR conditions will
prevail at both taf sites through taf period. With surface ridge
entrenched over northeast Minnesota and northwest
Wisconsin...winds will remain less than 10 miler per hour through
taf period.




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