Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 292334
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
534 PM CST Thu Jan 29 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 358 PM CST Thu Jan 29 2015

Although a few light flurries or sprinkles are still possible late
this afternoon, the secondary vort max which was providing weak
ascent will have moved east of the CWA by this evening. Gusty
northwest winds will start to subside overnight and turn northerly
in response to an area of high pressure which will be sliding into
the region. Overnight lows will be much cooler than last night due
to the colder post-frontal air mass.

Kanofsky

.LONG TERM:  (Friday through Next Thursday)
Issued at 358 PM CST Thu Jan 29 2015

The low level cloud cover should advect east of our forecast area
Friday morning as the upper level trough shifts well east of the
region and the strong surface ridge axis moves southeastward through
the forecast area on Friday.  Despite the solar insolation expected
the highs will be quite cold, although close to seasonal normals for
late January.  Mid-high level clouds will move into the region
Friday night ahead of the approaching storm system.  Rain should
spread northeastward into northeast and central portions of MO on
Saturday with increasing low-mid level moisture well ahead of the
southwestern US upper level low.  The NAM model was also depicting
mid level frontogenetical forcing across northeast MO and west
central IL south of an approaching cold front moving southward into
southern IA.  If the precipitation comes in early enough on
Saturday there could be a brief period of snow and sleet, but it
appears that the surface layer will warm up enough that most of the
precipitation on Saturday will be in the form of liquid rain.  The
precipitation should spread through the entire area by Saturday
evening and become heavier Saturday night as a strong northern
stream shortwave approaches our area.  Upper level divergence will
also be increasing over our region in the right entrance region of
an upper level jet streak over the Great Lakes region.  The rain
will change over to snow Saturday night as the cold front sags
southward through our area, along with increasing upward vertical
motion leading to more pseudo adiabatic cooling.  The better snow
accumulations Saturday night should be north and west of STL.
Precipitation in the form of snow will continue on Sunday for most
of our area as the upper level trough deepens over the region and a
surface low develops and moves northeastward through AR and into the
TN Valley region.  Prefer the GFS and ECMWF model solutions as the
NAM seems too deep with the surface low and a little too high on its
QPF.  There may be some lingering light snow or flurries Sunday
evening, but most of the accumulating snow should be over by this
time as a surface ridge builds southeastward into the region with
strong low level cold air advection and colder, below normal minimum
temperatures expected Sunday night.  Although there is still plenty
of model uncertainty it appears at this time that the highest snow
accumulations will likely occur across northeast MO and west central
IL with around 4-6 inches possible.  Lesser amounts of around 2 to 4
inches are possible further south across the rest of our area.
Later shifts may need to issue a winter storm watch for a portion of
the area as forecast confidence grows, and if the prefered models
indicate more QPF along with a quicker changeover from rain to
snow.  The GFS and ECMWF models had a northwest flow, clipper type
shortwave for Monday night, but it appears that any accumulating
snow with this system will be north of the forecast area.  A cold
front will drop southeastward through our region Tuesday night and
Wednesday morning as an upper level trough deepens over the Great
Lakes region.  This may bring some light rain/snow to our area,
followed by very cold temperatures for Wednesday night and
Thursday.

GKS

&&

.AVIATION:  (For the 00z TAFs through 00z Friday Evening)
Issued at 530 PM CST Thu Jan 29 2015

Primary concern for tonight and into early on Friday will be on
timing the dissipation/scattering out of MVFR ceilings across the
region. Current satellite imagery depicts OVC MVFR stratus deck up
into Minnesota slowly sliding south and east. Believe tonight will
continue to be overcast with scattering out of stratus by mid
morning. Surface ridge will move toward area by Friday afternoon
yielding light and variable winds.


Specifics for KSTL:

Primary concern for tonight and into early on Friday will be on
timing the dissipation/scattering out of MVFR ceilings. Current
satellite imagery depicts OVC MVFR stratus deck up into Minnesota
slowly sliding south and east. Believe tonight will continue to be
overcast with scattering out of stratus around 1400 UTC. Surface
ridge will move toward area by Friday afternoon yielding light and
variable winds heading into Friday night.

Gosselin

&&

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

$$

WFO LSX






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