Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150955
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
355 AM CST Mon Jan 15 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 355 AM CST Mon Jan 15 2018

Band of snow moving rapidly southeastward through our area,
currently extending from COU and JEF through the St Louis metro area
to 3LF.  This activity was ahead of a shortwave moving southeastward
through northern MO, and along and just ahead of a strong cold front
extending from a surface low over western WI southwest to near UIN
and COU.  This snow was progressing through our area a little
quicker than previous models had forecast, so will be able to cancel
parts of the winter weather advisory early across northeast MO into
west central IL.  This band of snow should drop around 1 inch of
snow.  Most of the accumulating snow after 12Z this morning should
be across southeast MO and southwest IL, southeast of STL. Most of
the accumulating snow should be southeast of our forecast area by
noon. With shortwaves continuing to rotate around the upper level
low moving into the Great Lakes region there may be a few flurries
or even snow showers this afternoon.  Strong and gusty northwest
winds behind the cold front will bring much colder air into the
region with temperatures falling through the day after passage of
the front. There will be a chance of flurries or snow showers across
northeast MO and west central IL late tonight with continued low
level cloud cover, and as colder mid level temperatures shift
southward into this area associated with the deep upper level low.
Very cold 850 mb temperatures will shift southward into our area
tonight down to around -18 to -20 degrees C.  This very cold air
mass, strong surface ridge building into our area from the northern
Plains, coupled with continued windy conditions will lead to wind
chills dropping down to -15 in the STL area to -25 near IRK by early
Tuesday morning.  The wind chill advisory will continue for tonight
and Tuesday morning for the entire forecast area.

GKS

.LONG TERM...  (Tuesday through Sunday)
Issued at 355 AM CST Mon Jan 15 2018

Mdls begin the period in good agreement with an upper trof swinging
thru the region with a reinforcing shot of cold air as a quite
strong sfc ridge builds into the region. The sfc ridge will continue
to build south Tues night with winds remaining nwly, but light. Have
trended temps below the cooler guidance, but with some question
regarding cloud cover, did not go quite as cold as tonight. If temps
are lowered a few degrees, another Wind Chill Adv may be needed for
at least portions of the area even with light winds.

Mdls continue to struggle with the upper low Thurs, which now tracks
north of the region. Because it remains north, there is no impact to
the area. However, have low confidence this will remain so due to
little run to run continuity.

By Thurs, the sfc ridge builds SE of the CWA allowing swly flow to
return to the region with the thermal ridge building into the area.
Mdls are in fairly good agreement with the approaching upper trof
and associated sfc low. There are some differences in timing with
good agreement between the GFS/GEM with the ECMWF a little slower.

Warming trends with snow cover are usually tricky and the going
forecast may not warm fast enuf. Still, have trended twd the warmer
guidance by Fri and continued thru Sun. Strong low system moves thru
the area on Sun bringing showers. While mdls do not currently depict
the need, thunder may need to be added with updates. The current
track, with the GEM a nrn outlier and some timing differences,
suggests mainly the nrn half to third of the CWA shud see some light
snow accums.


Tilly

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1131 PM CST Sun Jan 14 2018

A band of snow stretching across northern IL thru northeast MO
into western MO will continue to move southeast across the area
overnight and into Monday morning. Snow has already begun at KUIN
and should start at KCOU near the beginning of the TAF valid
period, then spread into the St. Louis metro region around 08Z.
Flight conditions will predominately be IFR within the band and
this is reflected in the TAFS. The longevity of IFR conditions at
the terminals could be a bit long and conditions might improve to
MVFR a bit sooner. The snow band should be south of all the
terminals by 14Z, with MVFR stratus and flurries continuing
through the remainder of the day. Current indications are that
stratus and flurries could also persist into Monday Night. A
strong cold front will move through the terminals in the wake of
the snow band accompanied by gusty northwest winds. The gusty
northwest winds will persist into Monday evening.

SPECIFICS FOR KSTL:

A band of snow stretching across northern IL thru northeast MO
into western MO will continue to move southeast across the area
overnight and into Monday morning. Snow should spread into the
terminal around 08Z. Flight conditions will predominately be IFR
within the band and this is reflected in the TAF. The longevity
of IFR conditions at KSTL could be a bit long and conditions
might improve to MVFR a bit sooner. The snow band should be south
of the terminal by 14Z, with MVFR stratus and flurries continuing
through the remainder of the day. Current indications are that
stratus and flurries could also persist into Monday Night. A
strong cold front will move through in the wake of the snow band
accompanied by gusty northwest winds. The gusty northwest winds
will persist into Monday evening.

Glass

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     26   2  14   6 /  90   5   5   5
Quincy          13  -3  11   1 /  10   5   5   5
Columbia        21  -2  10   2 /  30   5   5   0
Jefferson City  23   0  11   2 /  50   5   5   0
Salem           28   1  13   5 /  90   5   5   5
Farmington      27   2  14   3 /  90   5   5   0

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory until noon CST today for Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Pike MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

     Wind Chill Advisory from 6 PM this evening to noon CST Tuesday
     for Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis
     MO-Lincoln MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-
     Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint
     Charles MO-Saint Francois MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Shelby MO-Warren MO-Washington
     MO.

IL...Winter Weather Advisory until noon CST today for Bond IL-Calhoun
     IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Pike IL-
     Randolph IL-Saint Clair IL-Washington IL.

     Wind Chill Advisory from 6 PM this evening to noon CST Tuesday
     for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette
     IL-Greene IL-Jersey IL-Macoupin IL-Madison IL-Marion IL-
     Monroe IL-Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-
     Washington IL.

&&

$$

WFO LSX



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