Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 212150
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
350 PM CST Fri Nov 21 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 349 PM CST Fri Nov 21 2014

Will continue the chance of light rain as low level moisture
convergence and large scale ascent increases ahead of shortwave
trough currently moving towards us across the central Plains.  There
are two small areas of rain that have developed ahead of this
system...one over west central Missouri which will move into central
and northeast Missouri later this afternoon and a second over
northern Arkansas which will move into southeast Missouri.  Rain
chances will increase areawide this evening as aforementioned trough
moves across Missouri and Illinois.  Chances will continue through
the night as a 50kt low level jet sets up over the region which will
provide more low level moisture convergence.  At this time it still
appears that precipitation from this event will be mostly liquid as
dewpoints are steadily rising as rain moves into the area.  Both the
HRRR and RUC are showing that the surface wet-bulb temperatures will
be at or above freezing during the onset of precipitation through
early this evening with temperatures continuing to rise through the
late evening hours.

Britt

.LONG TERM:  (Saturday through Next Friday)
Issued at 349 PM CST Fri Nov 21 2014

At least scattered light showers can be expected Saturday and
Saturday night due to low-mid level warm air advection and as a
southwesterly low level jet continues to bring low level moisture
into the area.  The best chance of rain along with the highest
rainfall amounts should occur on Sunday as a southern stream
negatively tilted shortwave moves through the southern Plains and
into the TN Valley region, while an upper level low moves
southeastward into the northern Plains.  There will be upper level
divergence over our area between an upper level jet streak across
the southern Plains and another upper level jet streak across the
Great Lakes region.  A surface low will develop and deepen as it
moves northeastward through the St Louis area around 00z Monday.
There should be at least isolated thunderstorms across portion sof
central and southeast MO and southwest IL.  Temperatures will be
much warmer this weekend and above normal for a change.  Much of the
precipitation should shift east of our forecast area Sunday night as
colder and drier air filters southeastward into the region behind
the surface low and trailing cold front.  There may be some
lingering precipitation Sunday night into Monday morning as
shortwaves move through the area south of the upper level low which
will progress slowly eastward into the Great Lakes region.  The rain
may change over to some light snow across northeast MO and west
central IL late Sunday night and Monday as colder air continues to
advect into the region.  Temperatures will return to below normal
values beginning Monday with both the GFS and ECMWF models dropping
the -8 degree C 850 mb isotherm down to STL by 18z Monday.  Below
normal temperatures are expected from Monday through Thanksgiving
with little if any precipitation as a deep upper level trough moves
slowly eastward through the central US.  The ECMWF model does drop a
northwest flow, clipper type shortwave and associated weak surface
low southeastward through our area which could bring the potential
for a brief period of snow on Wednesday, but the GFS is much weaker
with this feature and only has very light QPF.  A strong surface
ridge will build southeastward into MO for Wednesday night and
Thanksgiving Day with unseasonably cold temperatures expected.

GKS

&&

.AVIATION:  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1230 PM CST Fri Nov 21 2014

Low based VFR or high MVFR will continue to move northeast across
the area this afternoon. Rain will begin to move into the area
later this afternoon into the evening hours, though the coverage
is not expected to great enough to warrant more than VCSH at this
point. Later this evening and overnight, a low level jet is
expected to develop over the region which will bring LLWS
conditions at all of the airports. These conditions will last
until around 14Z Saturday morning. Then low based VFR or high MVFR
are expected during Saturday with a low chance of rain.

Specifics for KSTL: Expect mainly low VFR conditions through the
day today until this evening when MVFR ceilings move into the area
with a chance of rain. Expect LLWS conditions overnight with
persistent MVFR ceilings before ceilings rise to VFR during the
day with a continued low chance of rain.

Britt

&&

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

$$

WFO LSX





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