Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 111201
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
601 AM CST Wed Jan 11 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 436 AM CST Wed Jan 11 2017

Latest surface analysis is showing that the cold front that moved
through the area yesterday has stalled over northern Kentucky and
Arkansas.  This front will move back northward today in response to
shortwave trough that is moving across the Rockies.  It will be
windy again today with a tightening pressure gradient between a
surface low over the central Plains and the high off the East Coast.
While winds will be in the 30-40 mph range, they look like they will
fall short of needing a wind advisory at this point.  Temperatures
again will climb well above normal into the upper 50s and 60s as
850mb temperatures be around 10C.

A cold front will drop south out of Iowa late this morning and early
this afternoon as a strong surface high drops southeastward out of
Canada.  Scattered showers will develop ahead of it this afternoon
in pockets of low level moisture convergence underneath some modest
mid level ascent.  Precipitation will continue into tonight as the
upper trough approaches the area.  There will be an increasing
chance of post-frontal precipitation tonight due to an increase in
low level frontogenesis.  Will have a small area of likely rain over
eastern Missouri into south central Illinois late this evening into
the overnight hours.  In addition, forecast soundings are showing
shallow cooling over northeast Missouri and west central Illinois
late tonight, so there is some potential that the rain will change
over to freezing rain or sleet.  Will have to watch for some trace
accumulations of ice in these areas.

Britt

.LONG TERM...  (Thursday through Tuesday)
Issued at 436 AM CST Wed Jan 11 2017

Primary concern remains icing potential across the CWFA from late
Thursday night through at least Saturday.  The synoptic pattern
hasn`t changed appreciably since yesterday.  A cold front will push
through the area Thursday and stall over central Arkansas between 06-
09Z Friday.  High pressure over the southeast U.S. will keep low
level warm moist flow straight off the Gulf of Mexico pointed right
at the front.  Forecast soundings continue to show a persistent
shallow, cold airmass over the CWFA with the warm moist air riding
up and over the cold air at the surface.  This should be an
excellent setup for freezing rain.  I think there will be a short
period of sleet at the onset of precipitation, but the main precip
type should be freezing rain.  Precipitation will overspread the
CWFA from the south starting between 06-09Z over the eastern Ozarks
and light precip should reach the I-70 corridor between 12-15Z
Friday.  Think most of the precip Friday should stay out of our
northern CWFA...but they`ll get in on the action Friday night as
the primary baroclinic zone aloft drifts northward.

Still some uncertainty on temperatures for Saturday and Sunday since
warm advection will be continuing through the period, and we will be
on the southern periphery of the Arctic airmass which will be moving
across the Upper Midwest and Great Lakes.  Generally went a few
degrees below guidance during this period since models tend to not
handle very shallow Arctic airmasses very well.  Current thinking is
that at least .1 to .5 inch of ice accumulation is likely across the
area with .25+ inch along and south of the I-70/I-64 corridors in
Missouri and Illinois respectively.

Temperatures should slowly warm up above freezing Saturday through
Sunday morning night from south to north.  Think temperatures may
hover around freezing in far northeast Missouri and west central
Illinois Sunday night and Monday morning, but this is far from
certain.  Temperatures should warm back above normal for Monday and
Tuesday with continuing chances for rain as another storm system
ejects northeast across the area.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 548 AM CST Wed Jan 11 2017

Expect mainly VFR conditions through the morning and early
afternoon hours until a cold front moves from northwest to
southeast across the area. Then MVFR ceilings can be expected
behind this front. There will be some precipitation along this
front, with scattered showers ahead of the front. Gusty south
winds will occur again today which will cause crosswinds east-west
runways.  Winds will veer northwesterly behind the front.

SPECIFICS FOR KSTL: Mainly VFR conditions are expected through 06Z
tonight. Southerly surface winds will be gusty once again today.
Then a cold front will move through the terminal after 06Z with a
chance of rain and ceilings falling into the MVFR category.

Britt

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     62  41  45  23 /  10  60  40  20
Quincy          57  26  30  15 /  30  30  20   5
Columbia        64  32  35  19 /  10  40  10  10
Jefferson City  68  35  37  22 /   5  50  20  20
Salem           61  52  54  25 /  30  50  60  30
Farmington      61  55  55  26 /  30  40  50  50

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Storm Watch from late Thursday night through Saturday
     afternoon for Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Madison MO-
     Moniteau MO-Montgomery MO-Osage MO-Reynolds MO-Saint
     Charles MO-Saint Francois MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Warren MO-Washington MO.

IL...Winter Storm Watch from late Thursday night through Saturday
     afternoon for Bond IL-Clinton IL-Madison IL-Marion IL-
     Monroe IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX



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