Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 211732

Area Forecast Discussion
National Weather Service La Crosse WI
1232 PM 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 18Z TAFS through 18Z Saturday afternoon)
Issued at 1232 PM CDT Fri Oct 21 2016

Main taf concern is wind shift at both RST/LSE taf sites this
afternoon/tonight. High pressure builds east of the area tonight
and allows winds to shift direction to the south this afternoon. Wind
speeds are expected to be up to 10 knots west of the Mississippi
River this afternoon into tonight. Weak upper level trough will
spread some mid to high level moisture across both taf sites this
afternoon into tonight. bases are expected to be
above 9000 feet. Expect VFR conditions to prevail at both RST/LSE
taf sites through period. With the passage of the upper level
trough...winds will shift to the west after 12z Saturday and wind
speeds will remain less than 10 knots.




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