Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 091113
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
513 AM CST Sat Dec 9 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 339 AM CST Sat Dec 9 2017

A shortwave over eastern IA early this morning will drop
southeastward through southwestern IL this morning.  Any measurable
snow should remain east of our forecast area, although there may be
a few flurries mainly across southwestern IL during the morning.  An
associated cold front will drop southeastward through our forecast
area this morning.  Relatively strong and gusty northwesterly
surface winds behind the cold front will bring in colder air into
northeast MO and west central IL today.  The sky will clear out this
afternoon from northwest to southeast as the upper level trough and
embedded shortwaves shift east of our region.  Temperatures will
drop quickly this evening due to a mostly clear sky along with
diminishing surface winds, but then as low-mid level warm air
advection increases with the surface wind backing around to a
southwest direction late tonight the temperature may become nearly
steady, particularly across northeast and central portions of MO.

GKS

.LONG TERM...  (Sunday through Friday)
Issued at 339 AM CST Sat Dec 9 2017

Not a lot of changes from yesterday. Going forecast is dry for
reasons mentioned below and therefore, focus continues to be temps.

Upper level pattern is expected to remain much the same with NW flow
aloft. This is the result of an upper level blocking event over the
wrn U.S. The block is expected to remain in place thru much of the
forecast period. Mdls are in good agreement with the block breaking
down sometime Fri with more zonal flow thru the weekend. However,
mdls tend to break down blocks too soon. That said, mdls also depict
a developing cyclone early next week along the nrn flank of the
block close enuf that it shud help to break down the block slightly.
The approaching trof later in the week wud then break down the
block. Still, believe this break down is too soon as the approaching
upper jet weakens.

Otherwise, forecast will largely depend on embedded shortwaves that
drop into the region. As mentioned yesterday, confidence in any s/w
is low much beyond 48 hrs. Have continued with a dry forecast as any
s/w continues to be forecast to remain north of the CWA. Can not
completely rule out flurries with any of these, but confidence is
too low attm to mention. Mdls are currently in agreement with a trof
digging into the area Thurs into Fri. However, mdls continue to
delay this with each cycle.

Have continued to warm temps for Sun and Mon with strong swly flow
and WAA. Otherwise, have trended twd a compromise.

Tilly

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 452 AM CST Sat Dec 9 2017

Cold front extending from a surface low over southern Lake
Michigan southwest through northern MO will move southeastward
through the taf sites this morning. Low level cloudiness around
2000-3000 feet in height will move southeastward through the taf
sites this morning. These clouds will clear out from northwest to
southeast this afternoon. Northwesterly surface winds will become
relatively strong and gusty later this morning, then diminish
this evening, backing around to a southwest direction by late
tonight.

SPECIFICS FOR KSTL: Cold front extending from a surface low over
southern Lake Michigan southwest through northern MO will move
southeastward through the STL area this morning. Low level
cloudiness around 2000-3000 feet in height will move southeastward
through the STL area this morning. These clouds will clear out
from northwest to southeast this afternoon. Northwesterly surface
winds will become relatively strong and gusty later this morning,
then diminish this evening, backing around to a southwest
direction by late tonight. The surface wind will strengthen again
Sunday morning.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     39  25  51  32 /  10   0   0   0
Quincy          33  21  45  28 /   5   0   0   0
Columbia        38  23  52  30 /   0   0   0   0
Jefferson City  38  22  52  30 /   0   0   0   0
Salem           38  22  45  28 /  10   0   0   0
Farmington      37  23  51  30 /  10   0   0   0

&&

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

$$

WFO LSX



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