Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 090543

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1143 PM CST Fri Dec 8 2017

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 222 PM CST Fri Dec 8 2017

This afternoon, the upper air pattern reflects a highly amplified
longwave RIDGE over coastal western North America and a TROF over
much of the middle and eastern portions of North America, with the
TROF axis extending from the Great Lakes southwestward to eastern
Texas.  Several imbedded shortwave disturbances existed within the
resultant N-NW flow aloft across the central and north-central
CONUS.  Only a few small areas of clouds exist across our region,
resulting in abundant sunshine for most locales.  Thanks to this
sunshine, temperatures have managed to rebound from the coldest
readings of the year back into the 30s.

With the TROF axis downstream of our region, flow aloft is almost
straight from the north in this highly amplified upper pattern. This
will open the door for a strong shortwave disturbance to drop down
late tonight and early Saturday morning.  The track for the
vorticity center looks no different than what it has the past couple
of days, with its western component tracking just east of the
Mississippi River.  This favors only a minimal chance for measurable
snow for the far eastern portions of the forecast area--east of
Vandalia and Salem in Illinois.  Elsewhere and further west, it
still looks like a stratocumulus field dropping down in strong low
level CAA and some forcing from the nearby vort center should be
able to result in a few periods of flurries late tonight and
Saturday morning.  By midday, a weakening/thinning cloud field, much
weaker CAA, and no upper support should end any very light pcpn.

Min temps tonight will be much warmer than last night, with mid to
upper 20s for most areas and this should be attained by midnight,
with steady to slowly rising temps towards daybreak with
strengthening SW to W flow.  Passage of a cold front early Saturday
morning and the gusty NW winds to result will keep temps from rising
much during the day despite what should be increasing sunshine thru
the day--with readings topping out in the lower to mid 30s most


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 222 PM CST Fri Dec 8 2017

The overall upper pattern will continue thru the middle of next
week, even at its current amplification; with model guidance then
hinting at a general flattening of the pattern for late next week.
Imbedded shortwave disturbances will also continue to be a theme,
but the models` ability to effectively resolve these will diminish
sharply beyond 2-3 days.  As it stands now, there are two potential
shortwave disturbances that could affect our region over the next
week, with more possible.  Otherwise, the pattern is strongly
supportive of regular shots of cold air from Canada separated by
brief warmups.  None of the cold air intrusions looks particularly
strong, however.

The first disturbance continues to look set for Monday with models
continuing to depict two distinct vorticity centers.  The eastern
one tracks too far northeast to have any real impact for us and the
western one looks weaker and much more sheared although its track
looks like it could impact our area.  Operational models, including
ensemble output, has gone with zero QPF and looks drier now than
24hrs ago.  Unless the eastern vort center tracks much more south or
the western vort center is less sheared and stronger, will continue
to go with a dry forecast here.

A second disturbance has been indicated for the middle of next week
for a few days now but there remains a large spread on its track
with the GFS suggesting more of an impact than the EC, which tracks
it well to the west.  This lies beyond the time period for when
these clipper systems can be evaluated well so will continue to side
with a dry forecast and monitor for developments.

No major cold air outbreaks this period, with Tuesday the next
chilly day with most days within a few degrees of seasonal averages.



.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1140 PM CST Fri Dec 8 2017

A cold front will plunge south through the region overnight into
Saturday morning. This front will be accompanied by increasing
northwest winds, MVFR flight conditions/CIGS, and scattered
flurries. Stratus will clear to the east of the region by early
afternoon with gusty northwest winds through the day, diminishing
early in the evening.


A cold front will move through the terminal overnight. This front
will be accompanied by increasing northwest winds, MVFR flight
conditions/CIGS, and scattered flurries. Stratus will clear to the
east of the region by midday with gusty northwest winds through
the day, diminishing early in the evening.



Saint Louis     29  35  23  48 /  10  10   0   0
Quincy          24  31  20  45 /  10  10   0   0
Columbia        26  35  22  50 /   5   5   0   0
Jefferson City  27  36  22  52 /   5   5   0   0
Salem           25  36  20  45 /  10  10   0   0
Farmington      24  35  20  51 /  10  10   0   0




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