Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 271130

Area Forecast Discussion
National Weather Service La Crosse WI
530 AM CST Mon Feb 27 2017

.SHORT TERM...(Today through Wednesday)
Issued at 239 AM CST Mon Feb 27 2017

Water vapor satellite this morning shows a long wave trough over
the West Coast with an embedded upper level low over Oregon. This
trough will advance east through the first half of the week with
several short wave troughs expected to get ejected out from it.
One of these short wave troughs will move across the region from
late tonight through Tuesday morning. A second short wave trough
will move across Tuesday night with a third moving over the area

The wave that comes in for tonight and Tuesday morning looks like
it will be able to produce some weak pv advection in the 500-300
mb layer that will move across the area late tonight into Tuesday
morning. As this wave comes in, a surface low is expected to form
over Nebraska today and then ride northeast on the weak cold front
that moved into the region Sunday. A weak band of frontogenesis
should form in the 1000-700 mb layer ahead of the low level warm
air advection and lift north across the area late tonight and
early Tuesday morning. The warm air advection is expected to
produce between 2 and 6 ubar/s of up glide on the 290K isentropic
surface. This system is will also bring in plenty of warm air
aloft that will result in a loss of ice in the clouds.
Fortunately, it looks like temperatures and dew points will not
cool much tonight to keep the majority of the precipitation as

As the area of low pressure moves past the area Tuesday afternoon,
the precipitation chances will start to decrease from west to
east. However, by Tuesday night, the forcing will start to return
ahead of the second short wave trough. This wave will take a more
southern track coming across Iowa into southern Wisconsin. The
third short wave trough for Wednesday will also take more southern
track, generally across northern Missouri into Illinois. Another
area of low pressure will form with these two waves and move along
the front and across Missouri into Illinois Wednesday. The best
frontogenesis will stay to the south of the area, but there could
be a weak band in the 700-500 mb layer across the south half of
the area Tuesday night. The isentropic up glide on the 285K
surface does not look as good and more in the 1 to 3 ubar/s range.
The forcing from these two waves looks to be enough to maintain a
chance across most of the area Tuesday night transitioning to just
the south and east by Wednesday afternoon. Precipitation type
concerns will continue Tuesday night into Wednesday morning as
there still should not be any ice clouds in place, but as cooling
aloft occurs Wednesday afternoon, the ice in the clouds should
gradually reform. Right now, the precipitation looks to be
extremely light Tuesday night and little if any icing should
occur. However, by Wednesday morning, some light glazing could
occur with a little bit more qpf possible, but amounts should
still only be a a couple hundredths of an inch or so.

.LONG TERM...(Wednesday night through Sunday)
Issued at 239 AM CST Mon Feb 27 2017

One the system goes by the area Wednesday, the upper level flow
looks to turn more to the northwest which will allow a fast moving
short wave trough to zip across the area late Wednesday night into
Thursday for a chance of mainly some light snow. Some more light
precipitation could occur Friday night as a zone of warm air
advection sets up ahead of a surface low over southern Canada. The
27.00Z GFS sets this warm air advection up farther south than the
27.00Z ECMWF. This results in the GFS showing some precipitation
over the area while the ECMWF keeps it well to the northeast.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 530 AM CST Mon Feb 27 2017

VFR conditions will prevail through the day with southerly winds
at 5-15 kts and some high cirrus at times. Clouds will lower this
evening and tonight ahead of an approaching weak low pressure
system. With low-level moisture transport increasing into the
region, expect ceilings to drop into the MVFR/IFR range around or after
midnight, with some fog possible. For now trended KRST into IFR
and KLSE into MVFR tonight, but even lower visibilities/ceilings
are possible, especially near the end of the TAF valid period. Showers
will also increase after midnight, with the higher chances at
KLSE. Low-level wind shear is a concern overnight tonight as a
low-level jet strengthens above light southerly surface winds.


Issued at 239 AM CST Mon Feb 27 2017

River levels continue to fall with only the Yellow River at
Necedah remaining above flood stage. This is expected to fall
below the flood stage later today. For more specific information,
see the latest river flood statement.




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