Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 300546

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1146 PM CST Tue Nov 29 2016

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 314 PM CST Tue Nov 29 2016

Stacked LOW system located over western MN will govern our upper
flow pattern over the next 24 hours.  A pair of areas of sheared
vorticity were in the fast southwest flow that exists to the south
of this system:  the first was over the STL metro area and was
helping to maintain a mid cloud deck just to the south, while a
second larger area was over much of OK, the northern TX panhandle
and into NM and was trying to do the same for areas just to its
south.  Skies were clear for areas to the north and west of STL
metro, but lurking further to the northwest was an extensive area of
low stratocumulus clouds.  At the surface, a cold front extending
from northeast to central MO was sliding east, with temperatures
rising into the upper 50s and lower 60s across much of our region.
It was yet another above average temp day with readings about 10-15
degrees above seasonal norms.

The sheared vorticity areas aloft will be the only real areas of
lift for our region and will help to either generate or maintain mid
cloud decks to the south of their axes and have maintained some
level of additional clouds for much of southeast MO and southern IL
tonight, while areas to the N and W remain clear thru at least
midnight.  The final axis of sheared vorticity should finally push
thru after midnight tonight and allow for clearing for areas to the
S and E of STL metro at the same time the leading edge of the
stratocu cloud deck enters northeast MO with this region of clouds
slowly pushing southeast towards daybreak and into Wednesday
morning.  Mostly cloudy to cloudy skies are then expected to prevail
for much of our region during the daytime on Wednesday.

Because of the clouds in varying areas at different times, temps
will be tricky tonight, but overall will have the best chance to
cool off for areas to the N and W that will both get the colder air
from the front first and stay clear the longest.  MOS had a decent
handle on this situation and followed closely.

With clouds blanketing much of the region on Wednesday and with a
cooler airmass in charge, have leaned cool against MOS for daytime
maxes, preferring the MET MOS for STL metro and areas to the N and
W, while going with a MOS blend elsewhere, with most staying in the


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 314 PM CST Tue Nov 29 2016

Dry and cooler weather conditions are expected Wednesday night
through the remainder of the work week as the slow moving upper
level low moves eastward through the Great Lakes region.  Any
precipitation should remain northeast of our forecast area.
Temperatures will be at or slightly below normal for early December.
The next chance for precipitation will occur Saturday night and
Sunday as a shortwave moves eastward through our area on the
backside of a retreating surface ridge shifting east of our area.
The ECMWF model is a little stronger with the shortwave and has a
little more QPF and also a larger area of precipitation than the GFS
model.  For now will just go with chance pops mainly late Saturday
night and Sunday morning.  It appears that the precipitation type
will be mainly rain, but could not rule out a little snow or sleet
mixing in late Saturday night/early Sunday morning.  No accumulation
is expected due to the light intensity of the precipitation along
with warm surface/ground temperatures and air temperatures likely
above the freezing mark for most of the time and most of our area. A
second round of precipitation which should be in the form of liquid
rain will occur Monday afternoon through Tuesday morning as another
shortwave moves through our area. Once again the ECMWF model is
stronger/deeper with the shortwave than the GFS and even has a
surface low reflection.  This second round of precipitation should
be a little more significant than the weekend precipitation with
slightly warmer temperatures and more low level moisture.



.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1133 PM CST Tue Nov 29 2016

VFR for the first 0-6 hours at all TAF sites. An expansive
stratocu deck will wrap around a stacked low pressure system and
reach the terminals after 30/12z. It is possible that cigs may
still be MVFR for a few hours at KCOU and KUIN before sufficient
daytime mixing causes cigs to rise to low-end VFR. The cloud bases
are expected to be VFR by the time the stratocu deck reaches the
St. Louis metro area. Westerly winds will increase and become
gusty by mid/late morning, then diminish after sunset.





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