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000
FXUS63 KLSX 101736
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1136 AM CST Tue Dec 10 2013

.SHORT TERM:  (Through Late This Afternoon)
Issued at 255 AM CST Tue Dec 10 2013

Early this morning:  longwave TROF axis was over our region with two
imbedded disturbances of note.  The first and more immediate one was
over northeast OK with another one over western MN.  At the surface,
a cold ridge of high pressure extended from OK thru our area and
towards Chicago with winds turning out of the SW in northern MO and
IA.  A surface lo reflection existed over southern MN.  Clouds were
exiting to the southeast with one departing event--it was cloudy for
areas south and east of STL--while another batch of clouds with the
northern upper level system were edging the MO/IA border.  The snow
appears to have ended for nearly our entire CWA with only some light
snow hanging on southeast of a SLO-SAR-FAM line, and this should be
gone around 10z.  Snow amounts were indeed in a narrow band of 1-2"
from near FAM to Dent County MO with generally a dusting or less
elsewhere.  Temps in northern MO have fallen to near zero earlier
tonight but thanks to southwest winds have risen a few degrees
since.  Temps remain in the upper teens and lo 20s under the
departing cloud cover southeast of STL.

Both upper level disturbances will be east of our area by 8am this
morning with NW flow and a lot of dry air in their wake.  Yet
another disturbance will rapidly approach from the NW by late this
afternoon, racing from the Pacific northwest by that time.

Under this setup, we should see nearly full sunshine for the lion`s
share of the day for our region, and thanks to SW-W surface winds, a
larger diurnal swing than we have seen in some time should result.
MOS temps seem to have a good handle on this and generally followed
with maxes from the mid 20s to the mid 30s.  The coldest temps will
be in northern MO with another new cold airmass edging there and the
warmest temps along the I-70 corridor where combo of lack of
significant snow cover and too far south for this cold airmass from
the north.  Did trim 2-3 degrees in parts of southeast MO and
southern IL for deep and fresh snow pack.

TES

.LONG TERM:  (Tonight through Monday)
Issued at 341 AM CST Tue Dec 10 2013

A shortwave will drop sewd through IA and nrn IL late tgt and
Wednesday sending a cold front sewd through our area late tgt and
Wednesday mrng. This should be a dry cold frontal passage through
our forecast area with the snow remaining north of our region,
ahead of the shortwave, although could not rule out flurries late
tgt across nern MO and w cntrl IL. Relatively strong caa can be
expected on Wednesday behind the cold front/850 mb trough. A
strong 1040 mb sfc ridge will move sewd through our area Wednesday
aftn and ngt. This will lead to good radiational cooling
Wednesday ngt and unseasonably cold low temperatures of about 15
to 25 degrees below normal. Will continue to go on the cold side
of MOS temperature guidance across portions of sern MO and swrn IL
with snow cover. Will see a warming trend beginning Thursday aftn
as the sfc ridge shifts se of the region and the sfc winds become
sly, while the upper level heights begin to rise. Precipitation
will likely spread newd into much of our area on Friday ahead of
an approaching upper level trough moving ewd through the srn
Plains. Still plenty of uncertainty with precipitation type, but
with an initially dry sfc/boundary layer as represented by
relatively low sfc dewpoints, the precipitation may begin as snow
and sleet with evaporative cooling as the sfc temperature falls to
the wet bulb. Across at least the srn or sern portion of our
forecast area it appears that the precipitation may change to
liquid rain Friday aftn with continued low-mid level waa. The
precipitation should change back to snow before ending late
Friday ngt after passage of a weak sfc low and cold front. Most of
the precipitation should shift east of our forecast area by
Saturday with lingering flurries as a second upper level trough
moves eastward through the area. Cooler temperatures can be
expected Saturday ngt through Sunday ngt as mid-upper level nw
flow returns to the area and a sfc ridge moves through the region
behind the cold front. The GFS model is colder than the ECMWF
model due to a stronger upper level trough/low over the Great
Lakes region and a stronger sfc ridge shifting sewd through our
area.

GKS

&&

.AVIATION:  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1123 AM CST Tue Dec 10 2013

VFR conditions continue thru tonight. Generally wly winds will
will back and diminish this afternoon and this evening. A cdfnt
will push thru the region Wed morning. Gusty nwly winds and a bkn
cloud deck around 2500 ft is expected just behind the cdfnt. For
UIN, with temps so cold, a brief period of flurries will be poss
with the lower cigs. These cigs and wind gusts shud dissipate late
in the period and thru the afternoon.

Specifics for KSTL: VFR and dry thru tonight. Gusty winds will
diminish during the afternoon and eventually back tonight ahead of
the next system. A brief period of MVFR cigs and gusty winds will
reach the terminal just after fropa Wed.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX