Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 282334

Area Forecast Discussion
National Weather Service La Crosse WI
634 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 00Z TAFS through 00Z Thursday evening)
Issued at 634 PM CDT Wed Sep 28 2016

Upper level low pressure continues to spin over the lower Great
Lakes, but with diurnally enhanced stratocumulus slowly expected
to fade through the evening hours as drier air wraps in from the
northeast. Later tonight, the big question will be potential fog
and/or stratus development with a fairly moist boundary layer in
place (especially places that saw some rain earlier in the day).
However, the limiting factor remains fairly strong winds just
above the shallow surface-based inversion. Hard to ignore guidance
signals hinting that RST may stand the best shot at a brief period
of IFR conditions with some fog development in lighter flow closer
to approaching high pressure, though confidence not high enough
just yet to take visibility below 2SM. At LSE, it does appear that
winds will be enough to preclude fog development at the airport,
but can`t rule out some river valley fog nearby and/or a brief
period of broken 300 foot ceilings from stratus. All of that stuff
should be history by around 14Z, with lots of dry air aloft
leading to plenty of clear skies through the day on Thursday.




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