Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 080922
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
322 AM CST Thu Dec 8 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 319 AM CST Thu Dec 8 2016

Water vapor imagery early this morning is showing that a confluent
upper trough is moving across the area.  The RAP is showing that the
trough axis will move quickly off to the east this morning.  The
forecast will remain dry today and tonight as subsidence sets in
behind the trough axis.  Expect skies to remain mainly clear over
the area as the RAP is showing the low level flow gradually
straightening out, and then becoming slightly anticyclonic by this
evening as high pressure moves in.

With strong cold air advection today, will go slightly cooler than
MOS highs and stay closer to SREF mean temps in most areas.
Northwest winds will stay up in the 5-10mph range tonight, so GFS
MOS lows look good in most areas.

Carney

.LONG TERM...  (Friday through Wednesday)
Issued at 319 AM CST Thu Dec 8 2016

The ridge axis will be over the eastern Plains on Friday morning.
Highs will struggle to reach the mid 20s to low 30s across the
area due to the cold start to the day. The ridge will will move
east of the Mississippi by 12Z Saturday which will turn the flow
back to the south. This should allow for a modest warm up on
Saturday...finally bringing temperatures above freezing during the
afternoon.

Models are coming into better agreement with the Saturday night-
Sunday night system.  GFS is trending to a less amplified shortwave
solution...more like the ECMWF.  This is producing less precip over
our CWFA late Saturday night and Sunday.  The best chance for precip
now looks to be Sunday night as the shortwave rolls through the
Mississippi Valley.  Precip types will be a little problematic.
Forecast soundings for Saturday night and early Sunday morning show
enough dry air in the column for any precip that reaches the ground
to fall as snow.  Warm advection ahead of the trof should eventually
turn any snow/mixed precip to rain by late Sunday morning/afternoon
except over northern portions of the CWFA where it may remain cold
enough for wintry precip.  Colder air moves in behind the trof so
rain will probably change back to snow Sunday night before ending.

Models diverge somewhat again toward the end of the forecast period.
Monday looks like a break in the weather with weak high pressure in
control...but another Arctic front will be headed south into the
Mississippi Valley on Tuesday.  There are differences on the speed
and strength of the front as it moves through our CWFA on Tuesday.
The GFS shows a more amplified upper level wave over the Great
Plains on Tuesday and the attendant cold front is also sharper and
the cold air advection behind the front is stronger than the
ECMWF. GFS also has a lot more precip than the ECMWF. Chance PoPs
still look appropriate given the uncertainties, but if the EC
trends toward the more amplified GFS chance PoPs won`t be high
enough. Both models build cold high pressure over the area on
Wednesday with ensemble guidance struggling to get highs into the
mid and upper 20s. If the GFS is right, 850mb temps will drop into
the -20 to -25C range. This would put lows in the low single
digits and highs in the teens for Wednesday. Not quite ready to
jump on that so am sticking close to the ensembles.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1130 PM CST Wed Dec 7 2016

Strong surface ridge over the northern Plains will build southeastward
into MO late tonight. West-northwest surface wind will strengthen
late tonight/early Thursday morning and become gusty. Some of the
2000-3000 foot cloudiness across IA may advect into UIN Thursday
morning, although it appears that most of the low level cloudiness
will remain north and east of the taf sites with mainly just some
high level clouds Thursday. The surface wind will weaken Thursday
night as the surface pressure gradient relaxes.

SPECIFICS FOR KSTL: Strong surface ridge over the northern Plains
will build southeastward into MO late tonight. West-northwest
surface wind will strengthen late tonight/early Thursday morning
and become gusty. Mainly just some high level clouds Thursday.
The surface wind will weaken Thursday night as the surface
pressure gradient relaxes.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     29  16  31  19 /   0   0   0   0
Quincy          24  13  26  15 /   0   0   0   0
Columbia        26  10  29  16 /   0   0   0   0
Jefferson City  28  12  29  17 /   0   0   0   0
Salem           29  17  29  18 /   0   0   0   0
Farmington      30  14  29  17 /   0   0   0   0

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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