Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 210812

Area Forecast Discussion
National Weather Service La Crosse WI
212 AM CST Tue Nov 21 2017

.SHORT TERM...(Today through Wednesday Night)
Issued at 212 AM CST Tue Nov 21 2017

Surface analysis at 2 am shows a deep 984mb low just north of Lake
Superior in southern Ontario with a trailing cold front extending
southward through central and southwest WI into IA. A secondary cold
front was pushing southeast out of northern MN/Dakotas.
Temperatures across the area as of 2 am ranged from the middle 30s
to middle 40s.

For today, that cold front over northern MN/Dakotas will surge
southeast across the area this morning which will usher in some
clouds and more impactful, gusty northwest winds and much colder
temperatures. Tight pressure gradient/cold air advection/downward
momentum will yield northwest winds in the 20-30 mph range with
gusts 30-40 mph. Not thinking a wind advisory is needed at this time
but will monitor wind/gusts closely. Also, looks like any snow
showers associated with the frontal passage should remain over far
northern WI/Upper MI. Cannot rule out a flurry or two northeast of I-
94 in steep low level lapse rate environment, but opted to keep a
dry forecast for now. So, plan on a cold/blustery day for the area
with highs only in the upper 20s  to the middle 30s.

Winds die down toward evening as a ridge of high pressure moves in.
Otherwise, look for a mostly clear cold night with lows dropping
into the teens.

Wednesday starts off mostly sunny, but plan on increasing high/mid
clouds through the day in response to warm air advection/isentropic
upglide ahead of low pressure dropping southeast through the
Dakotas. Highs are expected to be on the cooler side again with
readings in the upper 20s to middle 30s.

Mid-level trough/weak surface low continues to drop southeast
through the area Wednesday night. Increasing PV-advection/isentropic
upglide will result in a slight chance for some very light snow,
mainly along and north of I-94.

.LONG TERM...(Thanksgiving Day through Monday)
Issued at 212 AM CST Tue Nov 21 2017

A weak cold front slips through the area for Thanksgiving Day
resulting in a windshift and a few clouds. Otherwise, temperatures
will be near seasonal norms, in the upper 30s the the lower 40s.

Strong low pressure tracks across southern Ontario Friday, drawing
warmer downsloped Plains air into the region on breezy southwest
winds. A cold front from this low drops through the area later
Friday afternoon for the likelihood of some rain. Otherwise, expect
highs in the middle 40s to the middle 50s.

Weekend looks colder/dry as Canadian high pressure dominates the
Upper Mississippi River Valley Region. Look for highs mainly in the
30s. Monday looks a tad warmer with highs in the mid 30s/lower 40s.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1125 PM CST Mon Nov 20 2017

The area of low pressure continues to move east across southern
Ontario this evening and has pushed the pre-front trough across
much of the area. The winds will continue to turn to the
west/northwest behind this trough and then become gusty once the
cold front moves through late tonight. Good low level lapse rates
behind the front will allow gusts into the upper 20s to lower 30s
knot range to be common for much of the day after sunrise
Tuesday. These winds will then diminish near sunset as pressure
gradient relaxes and the speeds in the winds aloft diminish. An
area of MVFR/VFR clouds has formed across northern Minnesota and
North Dakota behind the cold front. The 21.00Z NAM and 21.03Z RAP
remain consistent in showing this moisture field spreading over
the airports Tuesday morning and then departing by early
afternoon. Some uncertainty on what the ceiling heights will be
when these clouds spread over the local area, but will go MVFR at
KRST and stay VFR at KLSE.




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