Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 282022

Area Forecast Discussion
National Weather Service La Crosse WI
322 PM CDT Wed Sep 28 2016

.SHORT TERM...(This evening through Thursday)
Issued at 322 PM CDT Wed Sep 28 2016

Primary challenge this evening and overnight will be cloud trends,
which in turn will impact temperatures and possible fog development.
GFS/NAM/RAP relative humidity fields show low-level drying from
east to west overnight with fingers of higher moisture remaining
across the western forecast area through 12Z Thursday. This idea
matches current satellite imagery with more cumuliform clouds
mainly along and east of the MS River with a thicker stratus deck
back across central IA into south-central MN. Thus, current
thinking is for cloud cover to slowly dissipate from east to west
this evening and overnight with at least areas of clear skies
across WI by daybreak Thursday. Would expect coolest temperatures
and possible fog development in these areas with lows possibly
into the lower 40s in favored cool spots of the cranberry bogs.
Further west, upper 40s to near 50 degrees is more reasonable.

Thursday will be partly to mostly sunny as high pressure ridge
nudges east toward the forecast area. Temperatures will be in the
60s to near 70 degrees with a light northerly wind.

.LONG TERM...(Thursday night through Wednesday)
Issued at 322 PM CDT Wed Sep 28 2016

Thursday night through Saturday, 28.12Z model suite now in good
agreement, lifting a cut-off closed low currently across the lower
Great Lakes north and westward. This will result in increasing
clouds from southeast to northwest Friday and Friday night as
increasing wrap around mid-level moisture moves across the Upper
MS River Valley. Did introduce some 20 POPs across far southwest
WI Friday afternoon, but much of the day expected to be dry.
Temperatures will be cloud dependent with highest values across
southeast MN into central WI.

Saturday, however, will be cloudy and cool with periods of
scattered showers as deeper moistening works into the region.
Doesn`t appear to be a wash out, but occasional showers dropping a
few hundredths of an inch at a time are possible. Highs will only
be in the lower to mid 60s with light northeast wind.

Will keep Sunday dry for now as closed low gets shoved eastward in
response to a deepening trough across the western CONUS. However,
the ECMWF still hangs onto a few lingering showers, so may need
to slow eastward exit of precipitation in future forecasts. Monday
into Tuesday look mainly dry and warmer with short-wave ridging
aloft. Expect highs in the upper 60s to lower 70s.

Next best chance for showers and thunderstorms will be Tuesday
night into Wednesday as the aforementioned western CONUS trough
moves into the nation`s mid-section. For now, chance POPs are
reasonable until additional details emerge.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1220 PM CDT Wed Sep 28 2016

MVFR/VFR clouds decks will continue to rise thru the afternoon with
diurnal warming and influx of some drier low level air. The diurnal
warming/mixing will result in steeper low level lapse rates this
afternoon, with isolate to sct -shra across the area thru about 23z.
Clouds then expected to decrease/clear thru the early/mid evening
hours with some stronger low/mid level subsidence and a drier 925-
700mb airmass rotating from the northeast. Next concern then
overnight into early Thu morning is radiational valley BR/FG
formation under what would be clear/mostly clear skies, light winds
and the moist boundary layer. However, winds just above the boundary
(around 500 ft agl) expected to be NE in the 15-20kt range which is
not favorable for widespread radiational valley/low laying area
BR/FG. Limited mention in KLSE TAF to BCFG in the 10-13Z time period
as there may some BR/FG hugging the bluffs around sunrise Thu. Other
than that, Thu looking to be good VFR area-wide under clear/mostly
clear skies.




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