Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 181514
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
914 AM CST Thu Dec 18 2014

.UPDATE:
Issued at 910 AM CST Thu Dec 18 2014

In the process of tweaking forecast based on latest snowfall obs.
Overall, snowfall should be winding down over the next few hours,
with greatest additional accumulation from mid MO into central IL.
Think additional accumulation in this band should be less than
1/2" since melting seems to be offsetting some of the
accumulation, but echo is a bit convective looking, so isolated
additional snows of an inch certainly not out of the question.

Will drop advisory for our far s counties, since most of the
snowfall the rest of this morning will be north of these areas.
Elsewhere headline remains the same. No expansion planned, since the
region has experienced the most adverse conditions from a travel
point of view.

Truett

&&

.SHORT TERM:  (Through Late This Afternoon)
Issued at 323 AM CST Thu Dec 18 2014

Vigorous little shortwave over northern Kansas is producing a broad
area of snow over parts of north central Missouri back toward west
central Missouri.  The going forecast looks pretty good in general;
however current radar and latest short range model guidance suggests
that there will be more precipitation across parts of northeast
Missouri and west central Illinois than previously forecast.  Low to
mid level frontogenesis and isentropic lift will increase through
15Z as the wave passes north of the area.  The shortwave should be
dampening out as it moves into an area of longwave ridging, so
precipitation should be on the decline through the morning, and
there is still a wedge of low level dry air to overcome, but
measurable precip does look likely across most of the area.
Accumulations still look pretty light with most areas receiving an
inch or less except for parts of central and southeast Missouri
where an inch or two of wet snow is likely to accumulate.  With
temperatures hovering right around freezing, expect some slick spots
on any untreated roads this morning, but temperatures should be
rising above freezing in most locations by mid to late morning so
that should alleviate any road issues.  Additionally, expect precip
to be winding down pretty rapidly after 15Z as the shortwave dampens
out and the primary band of frontogenesis and isentropic lift
weakens.  The one place where there may be lingering problems is
northeast Missouri and west central Illinois where temperatures may
struggle to break freezing this afternoon.

Carney

.LONG TERM:  (Tonight through Wednesday)
Issued at 350 AM CST Thu Dec 18 2014

Relatively quiet weather will prevail over the area for the rest of
the week with a large surface ridge extending from southern Canada
through the Upper Midwest and Great Lakes region down into the
Mid-Mississippi Valley.  Another wave will ripple through in the
quasi-zonal flow aloft Friday night.  The lower atmosphere looks too
dry to allow any precip to reach the ground from this wave...all
except for southern portions of the area.  Have kept chance/slight
chance PoPs across southeast Missouri and southwest Illinois with
little or no qpf associated with them.

Saturday and Sunday look warmer with southwest flow deepening ahead
of the next trof with temperatures rising to around normal on
Saturday and above normal on Sunday.  Medium range guidance looks to
be in good agreement that the trof will deepen across the Central
U.S. Monday into Wednesday.  This should bring us another period of
cloudy and occasionally rainy weather with the best probabilities of
precipitation Monday night into Tuesday.  The atmosphere will likely
be too warm for much frozen precipitation until possibly Tuesday or
Tuesday night.  QPF looks pretty light on the GFS and ECMWF by the
time the atmosphere is cold enough to snow, but there may be a few
periods of flurries or light snow Tuesday and Tuesday night.

Carney

&&

.AVIATION:  (For the 12z TAFs through 12z Friday Morning)
Issued at 547 AM CST Thu Dec 18 2014

Fun today will be chasing ceilings and visibilities. Weather
system will lift northeast fairly quickly so any snow that greatly
reduces visibilities should end by Midday or shortly after.
ceilings are mainly dropping to mvfr with some ifr showing up in
places. Guidance really brings in fog and ifr by 12 Thursday.
Moist atnmosphere with light winds so can`t argue with that.

Specifics for KSTL: Will likely amend shortly as it looks like the
visibiity will be dropping quicker then previously thought. A
couple of hours of 2-3sm sn looks likely, then up to 5 or more
the rest of the. Best lift drops off dramatically after 18z so
don`t expect much this afternoon, except for some fog and mvfr.
Ifr ceilings expected by 12z Thursday with fog.

JPK

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...WINTER WEATHER ADVISORY until 10 AM CST this morning FOR Boone
     MO-Callaway MO-Cole MO-Crawford MO-Gasconade MO-Moniteau MO-
     Osage MO-St. Francois MO-Washington MO.

IL...NONE.
&&

$$

WFO LSX





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