Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 120520

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1120 PM CST Mon Dec 11 2017

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 317 PM CST Mon Dec 11 2017

The clipper centered over central Illinois will move rapidly east
late this afternoon and evening.  A strong pressure gradient between
the surface high building into the northern Plains and the clipper
is producing strong and gusty wind this afternoon.  Sustained wind
between 20-25kts with gusts to 35-40kts are being reported...and
Quincy actually came in with a 30G43kt report at 200 PM.  The strong
wind is expected to continue for the remainder of the
afternoon...but should diminish somewhat this evening as the
secondary cold front which is now over Iowa comes through the area.
The truly cold air is still up over Minnesota, but it should be down
into Missouri by Tuesday morning, so expect low temperatures to fall
into the 20s.  Light precipitation over Iowa associated with the
strong vort may graze our northern counties this evening with some
sprinkles or flurries before moving off to the east.  The
stratocumulus deck north of us will rotate down into the area
tonight...but should clear out by early Tuesday morning.  However
cold advection on Tuesday will likely limit the diurnal rise to only
10-15 degrees so highs should top out in the 30s in most locations.


.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 317 PM CST Mon Dec 11 2017

High amplitude pattern aloft will persist at least through the end
of the week with a strong upper level ridge over the West Coast and
a deep longwave trof over the East Coast.  This will keep the
Mississippi Valley in northwest flow aloft with at least 2 more
shortwaves diving through the region through Friday.  The surface
reflection of each shortwave will produce warm advection ahead of it
and cold advection behind it...continuing the roller coaster
temperatures for the region.  Unfortunately there looks to be little
if any relief from the ongoing drought with these systems as
moisture remains limited.

Medium range models are indicating a pattern shift this weekend.
Flow becomes more zonal on Saturday and then southwesterly Saturday
night as a shortwave moves through the central U.S.  The EC and GFS
differ on how fast and how strong the wave will be.  Given the lack
of agreement will stick with ensemble guidance for Saturday through
Monday which is pretty mild with highs in the 40s and 50s and lows
generally in the 30s.



.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1111 PM CST Mon Dec 11 2017

Stratus producing MVFR flight conditions blankets the region and
extends north into eastern IA. There should be a steady north to
south clearing trend overnight and through daybreak on Tuesday
morning. VFR flight conditions are then expected at all the
terminals the remainder of Tuesday morning through the evening.
Gusty northwest winds will continue overnight, gradually
diminishing from west to east on Tuesday.


Stratus/MVFR flight conditions will continue overnight with
clearing anticipated around daybreak. VFR flight conditions are
then expected the remainder of Tuesday morning through the
evening. Strong and gusty northwest winds will continue
overnight, gradually diminishing on Tuesday morning, however
occasional gusts will continue into the afternoon.





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