Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 122317

Area Forecast Discussion
National Weather Service La Crosse WI
617 PM CDT Mon Mar 12 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 149 PM CDT Mon Mar 12 2018

Main forecast concern in the short term will be light snow/flurry
chances in the northeast part of the forecast area this
evening/tonight. An upper level short wave will move southward
through Wisconsin late this evening. RAP soundings have generally
shown saturation above 900 mb, though also show near-surface levels
remain mixed/dry. May be tough to get anything through the dry
layer, but 12.12Z NAM soundings show a bit better saturation in
these lower levels for a brief time. Have elected to keep slight
chance PoPs in the far north, with flurry/sprinkle chances farther
south along and northeast of Interstate 94. High pressure will build
in on Tuesday, with breezy northwest winds once again. Anticipating
highs in the lower to mid 30s, but if cloud cover is sparse like
Monday, may need to bump those up a bit.

.LONG TERM...(Tuesday night through Monday)
Issued at 149 PM CDT Mon Mar 12 2018

12.12Z models have remained consistent in showing an extended
period of quiet weather for the region. The upper level pattern
looks to slowly evolve this week as the large trough over the
eastern part of the continent moves slowly to the east. This will
allow the upper level ridge currently over the Rockies, to become
established over the Missouri River Valley by Thursday. In the low
levels, a cold front will pass through the region Wednesday in
association with a short wave trough moving into the eastern long
wave trough, but this is expected to pass through without
producing any precipitation.

As the upper level ridge moves east, a cut off low and long wave
troughing will form behind it along the West Coast. The models
have been suggesting a short wave trough will get ejected from
this system and impact the region starting Friday. What the models
have not been consistent on is whether this will come through as a
strong short wave trough with an upper level low and pass by south
of the area like the 12.00Z ECMWF is showing or whether the short
wave trough will be weaker and move over the top of the ridge with
more of a direct impact on the area like the 12.12Z GFS is
showing. After this system moves by, both models then suggest the
ridge will temporarily re-establish itself over the region for
Saturday into Sunday. After that, the remains of the Pacific
system should be moving toward the region but differences on how
this is handled. The ECMWF suggests a rather strong northern
stream system will move rotating south across eastern Canada and
will push the remains of the Pacific system south of the region.
The GFS does not show this northern stream influence and brings
the Pacific system right across the area as a strong short wave
trough and upper level low. Averaging out these differences will
lead to a small chance of some light rain/snow Friday night and
Saturday with another chance for Sunday night into Monday.

The overall pattern is expected to allow for temperatures to
moderate early in the period and be near the seasonal normals
Wednesday through Friday. Potential for a bit more warming over
the weekend with some 50s possible across the south. Overnight
lows should generally be in the 20s.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 617 PM CDT Mon Mar 12 2018

General VFR conditions in place with northwest flow across the area.

Main aviation forecast concern is extent of broken cloud deck over
mainly Wisconsin and how things will trend as short wave drops into
western Great Lakes. Short term models continue to overdue ceilings
so chose a bit more optimistic approach with general quiet stretch




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