Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 120946

Area Forecast Discussion
National Weather Service Saint Louis MO
346 AM CST Tue Dec 12 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 345 AM CST Tue Dec 12 2017

Clouds currently across the area are expected to exit the sern
portions of the CWA by mid morning. Some CU shud form along the nrn
flank delaying the clearing after sunrise. As the low system that
brought the strong gusty winds yesterday pulls ewd out of the
region, winds will diminish thru the morning and gradually become
wly. With few clouds expected today, have trended twd the warmer
guidance despite the nwly winds.

Winds become fairly light this evening with few clouds expected.
This shud allow for temps to drop quickly with sunset. Winds are
expected to become sly to swly and increase late tonight ahead of
the next clipper. This shud cause temps to become steady overnight
and slowly rise late tonight into Wed morning. Still, with the dry
air expected across the region, have trended twd the cooler guidance
expecting temps to drop quickly this evening especially in sheltered

With the very dry air in place and strong winds with gusts to 20 to
25 mph, much of the area will see heightened fire danger today.
While relative humidity values will drop into the lower 20 percent
or even into the teens, conditions are not as extreme as yesterday
with much lighter winds anticipated today.


.LONG TERM...  (Wednesday through Monday)
Issued at 345 AM CST Tue Dec 12 2017

Warmer temperatures on Wednesday due to low-mid level warm air
advection and southwest surface winds during the morning.  A
shortwave and associated cold front will move southeastward through
our area on Wednesday, but it appears that any precipitation will be
north and east of our forecast area along and left of the track of a
southeastward moving surface low where better low level moisture
will exist.  Colder conditions can be expected on Thursday well
after the passage of the cold front and as a strong surface ridge
builds into our area from the Plains. The operational GFS model, in
particular is now showing the potential for at least light QPF
across mainly central and southeast MO Thursday night, ahead of a
positively tilted upper level trough with embedded shortwaves and a
weak surface low reflection. The NAM model has only very light QPF
for our area, and the ECMWF is weaker at the surface and does not
have any precipitation for our area. For now will just include
slight chance pops across central into parts of southeast MO
Thursday night.  The temperature profile supports a precipitation
type of snow.  A warming trend will begin Friday afternoon due to
rising upper level heights, and surface winds backing around to a
southwest direction. Highs on Saturday should be at least 10 degrees
above normal for mid December.  The latest models were showing more
favorable conditions for precipitation on Sunday as another
positively tilted upper level trough approaches with a weak surface
wave moving along an associated cold front.  The best chance of
precipitation should be across southeast MO and southwest IL, just
north of the surface wave.  The ECMWF model solution is less
progressive than the operational GFS as it develops a southern
stream upper level low and keeps precipitation going into Monday
morning.  At this time this solution appears to be an outlier and
will lean toward the more progressive solution and end pops by
Sunday night.  It appears that the temperature profile will be warm
enough that this precipitation will be liquid rain.



.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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