Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240546

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1146 PM CST Thu Nov 23 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 309 PM CST Thu Nov 23 2017

Weak cold front/trof to washout by early this evening. So will have
clear skies and light south to southwest winds. Lows to be a bit
warmer than this morning`s lows, in the 30s.

On Friday, southerly flow to pickup ahead of next frontal boundary,
bringing in decent WAA, with highs 15 to 20 degrees above normal, in
the 60s under partly sunny skies. Moisture will be limited with
frontal boundary, but could see some sprinkles with weak forcing
along and behind front from mid cloud deck after 21z Friday for
northern portions of forecast area as front begins to move through.


.LONG TERM...  (Friday Night through Next Thursday)
Issued at 309 PM CST Thu Nov 23 2017

Main focus thru the forecast period will be temps with low chances
of precip thru the period.

Forecast period begins with a cdfnt pushing thru the area Fri night.
Not much moisture is available for this front, however, with a sharp
upper trof associated with it and a sfc trof just ahead of the
front, some sprinkles are possible ahead of the front as it passes
thru the CWA.

Mdls are in good agreement through about Mon. A large sfc ridge
builds into the area behind the front and have trended twd the
cooler guidance for Sat with nly flow and cool 925mb temps, despite
ample insolation. Temps rebound quickly for Sun as sfc winds become
sly to swly and the thermal ridge builds into the region. Sun and
Mon shud see temps some 10+ degrees above seasonal average.

Mdls differences appear by Mon and result in a low confidence
forecast for the remainder of the forecast period. Important
differences actually show up by Sun which may result in Sun being
slightly cooler and Mon/Tues warmer than currently forecast. Trends
will need to continued to be monitored. Regardless, have trended
slightly cooler for Tues with an approaching cdfnt. With changes to
timing of the front on Tues and into Wed once again, have continued
low PoPs. If the ECMWF verifies, can not rule out a low chance of
frozen precip, but this seems unlikely.

With such large differences among the explicit models as well as the
GEFS, have kept PoPs low and trended temps twd a compromise for now.



.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1145 PM CST Thu Nov 23 2017

VFR conditions to prevail through the period. High clouds over
northwest MO will continue to stream southeast overnight and into
the day on Friday. Southwesterly winds will increase late Friday
morning into Friday afternoon, with gusts of 20-25 knots likely
ahead of a cold front. This cold front will push through all sites
Friday evening, bringing a wind shift to the northwest along with
some enhanced mid/high cloudiness.

Main TAF concern will be crosswind potential on the parallel
runways Friday afternoon. Southwest winds will increase by late
Friday morning, with gusts of 20-25 knots possible Friday
afternoon. Otherwise, a cold front will bring a wind shift to the
WNW Friday evening with some increase in mid/high cloudiness.





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