Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191110

Area Forecast Discussion
National Weather Service La Crosse WI
610 AM CDT Mon Mar 19 2018

.SHORT TERM...(Today through Wednesday)
Issued at 205 AM CDT Mon Mar 19 2018

The only chance for some precipitation in the first half of the
week continues to be centered on Tuesday. An upper level low over
Kansas this morning will move east across the central Mississippi
River Valley today and into the Ohio River Valley tonight. In the
wake of this system, northwest flow will be established over the
Upper Midwest with a short wave trough expected to drop out of
Canada Tuesday and into the back side of the Ohio River Valley
system. This wave will primarily stay to the west of the local
area but get close enough to produce some weak pv advection in the
500-300 mb layer west of the Mississippi River. The forcing from
the short wave trough may be aided by a band of weak frontogenesis
in the 850-500 mb layer. However, that looks to be about all there
will be for forcing with this system and the concern becomes
whether this will be enough to produce saturation and allow some
light precipitation to occur. An area of high pressure will be
centered over Ontario that will set up a dry northeast low level
flow into the area. This will keep the best axis of moisture west
of the Mississippi River, but it looks to be elevated with a
pronounced dry wedge below 800 mb. The 19.00Z NAM and GFS both
indicate most of the precipitation should stay west of the
forecast area and plan to only have 20 to 30 percent across the
west for this system.

.LONG TERM...(Wednesday night through Sunday)
Issued at 205 AM CDT Mon Mar 19 2018

Upper level ridging will work east out of the Rockies and over the
Midwest late in the week. Troughing will be along the West Coast
with an upper level low over the Pacific off the British Columbia
coast. The concern becomes how quickly short wave troughs coming
out of the western system will be able to work through the ridge
and into the region. The 19.00Z GFS and ECMWF both suggest the
ridge axis should move across and east of the area Friday or
Friday night allowing a short wave trough to come in from the
west. This wave should move past the area Saturday night before
the remnants of the upper level low start to move out of the
northern Rockies out on the High Plains and into the Upper
Midwest. Still plenty of model differences to be reconciled as the
GFS is much stronger with the short wave trough for Friday night
and Saturday than the ECMWF and then looks to be faster and
stronger with the remains of the Pacific system.

Both models develop a surface low over Kansas Friday with the
first short wave trough and then move it east into the Ohio River
Valley. A band of warm air advection precipitation is expected to
develop ahead of this system and move into the area Friday
afternoon with the deformation band then tracking across the area
to the north of the low Friday night into Saturday. Temperatures
with this system look to be warm enough for rain or a rain/snow
mix during the days and the cool enough for mainly snow Friday
night. With the differences in the handling of the Pacific low,
the GFS brings more precipitation in for Sunday and Sunday night
while the ECMWF is essentially dry for this period.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
Issued at 610 AM CDT Mon Mar 19 2018

Use KARX WSR-88D VAD sfc-8K ft VAD winds with caution again this
morning. The spring bird migration is still on. 925-850mb winds
progged by models to be east 10-20kts, yet VAD winds again south in
the 20-30kt range.

With the easterly, and drier, sfc-850mb flow VFR conditions expected
to prevail this period. Clouds thru today/tonight looking to be sct-
bkn in the 6K-8K ft range. A tighter pressure gradient across the
area later this morning and this afternoon to result in NE winds
around 10kts, gusting 15-20kts at some of the higher terrain, open
country areas like KRST.




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