Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 082022
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
222 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
areas.

TES

.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.

TES

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1150 AM CST Fri Dec 8 2017

VFR conditions and dry weather will prevail at the TAF sites thru
this evening. A clipper system will edge our region late tonight
and early Saturday morning, with any threat for accumulating snow
well east of the TAF sites. Did add some flurries mention for
sites near the MS river with the arrival of MVFR CIGs and gusty NW
winds after midnight and at least thru a part of Saturday morning,
with CIGs raising into VFR category during late morning and
dissipating during the afternoon.

SPECIFICS FOR KSTL: VFR and dry until around 10z, but with arrival
of lower stratocumulus CIGs should also come a wind shift from NW
and gusty and scattered flurries. Some improvement is anticipated
by late morning with loss of scattered flurries as well.

TES

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     29  35  23  49 /  10  10   0   0
Quincy          24  31  20  46 /  10  10   0   0
Columbia        26  35  22  51 /   5   5   0   0
Jefferson City  27  36  22  53 /   5   5   0   0
Salem           25  36  20  44 /  10  10   0   0
Farmington      24  35  20  50 /  10  10   0   0

&&

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

$$

WFO LSX



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