Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 211108

Area Forecast Discussion
National Weather Service La Crosse WI
608 AM CDT Fri Oct 21 2016

.SHORT TERM...(Today and tonight)
Issued at 256 AM CDT Fri Oct 21 2016

Elongated surface ridge from Hudson Bay to TX will bisect the
forecast area today and tonight, resulting in dry conditions and
light winds with periodic clouds per upstream satellite imagery
and model relative humidity profiles. Perhaps a degree or two
warmer than yesterday with afternoon highs from the upper 40s to
lower 50s. Increasing clouds overnight and modest warm air
advection will keep lows tonight slightly elevated from the mid to
upper 30s.

.LONG TERM...(Saturday through Thursday)
Issued at 256 AM CDT Fri Oct 21 2016

Short-wave ridging aloft with light southerly return flow on the
backside of the departing high will result in warmer conditions
for Saturday with highs from the mid 50s to lower 60s. Temperatures
Sunday will be dependent on the timing of a relatively strong cold
front. For now, highs appear to top out again in the mid 50s to
lower 60s by early afternoon before dropping through the rest of
the day. All rain with this front looks to remain north of the
forecast area nearest to the deepest moisture and best forcing.
Primary sensible weather impact across the Upper MS River Valley
will be an abrupt shift in winds to the northwest, gusting at
times up to 25 mph, especially west of the MS River.

Dry conditions continue for Monday with ridging aloft across the
region. However, temperatures will be noticeably cooler in the
wake of Sunday`s frontal passage, with highs back into the 50s.

Big weather story for next week continues to be Tue/Wed as a
potent eastern Pacific short-wave undercuts the ridge and moves
across the central Plains. 21.00Z GFS/ECMWF now in relatively
good agreement showing a lee cyclone over western KS at 18Z Tues
lifting northeastward and moving along the I-80 corridor across IA
and into IL through 00Z Thurs. GFS is a tad faster than the ECMWF,
but both models drape a strong east-west oriented 850 hPa thermal
gradient across the forecast area, serving as the focus for a
prolonged rain event Tues into Wed with POPs now at 60 to 80
percent. Strong isentropic lift along the elevated boundary
combined with PWATs increasing to around one inch from an influx
of Gulf of Mexico moisture could result in periods of moderate to
heavy rain. That said, models have backed off on instability with
roughly 250 J/kg or less of 0-6 km MUCAPE along and south of the
I-90 corridor. Will keep isolated thunder mention in these areas,
but something to watch over the next several days.

Thursday and beyond, there are large model differences in the 500
hPa flow pattern, resulting in a low confidence forecast. Will
follow consensus POPs with periodic slight chances to end the
week. No foreseeable large changes in air mass with highs in the
50s and lows in the 40s.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 608 AM CDT Fri Oct 21 2016

Look for varying amounts of mid/high level cloudiness through the
TAF period as a ridge of high pressure lingers over the Upper
Mississippi River Valley Region. Otherwise, VFR conditions
expected with light and variable winds.


WI...Frost Advisory until 8 AM CDT this morning for WIZ032-033-041-

MN...Frost Advisory until 8 AM CDT this morning for MNZ079-088-096.

IA...Frost Advisory until 8 AM CDT this morning for IAZ011-030.



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