Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 091811

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1211 PM 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.


.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.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1155 AM CST Sat Dec 9 2017

Dry and VFR conditions will persist through Sunday afternoon.
Cloudiness associated with cold front passage will continue to
erode from west to east as the parent low located in lower
Michigan continues pushing northeast. Most TAFs will likely only
see a few mid and high level clouds overnight. There will be yet
another front that will approach the region between 6z and 12z
Sunday with only mid and high clouds expected. Winds will pick up
briefly out of the southwest ahead of the front then decrease
behind the front.


Dry and VFR conditions expected for the terminal through Sunday
afternoon. Ceilings are expected to improve as cloudiness will
continue to push east as the cold front and parent low in lower
Michigan continues to push away from the region. The terminal
will likely only see a few clouds overnight. Winds will pick up
briefly out of the southwest around 16z during a frontal passage
on Sunday.



Saint Louis     39  25  51  30 /   5   0   0   0
Quincy          33  21  45  27 /   0   0   0   5
Columbia        38  23  52  30 /   0   0   0   0
Jefferson City  38  22  52  30 /   0   0   0   0
Salem           38  22  45  27 /  10   0   0   5
Farmington      37  23  51  29 /   5   0   0   0




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