Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 140500
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1100 PM CST SAT FEB 13 2016

.UPDATE:
Issued at 941 PM CST Sat Feb 13 2016

Radar is showing mid-level banding extending from west central
Illinois into south central Illinois at this hour. Haven`t
received any surface reports of snow as dry low level easterly
flow is sublimating any snow before it reaches the ground.  Do
still think that chances of snow will increase late this evening
into the overnight hours as large scale ascent increase ahead of
shortwave trough dropping southeastward out of the northern
Plains. At the same time low-mid level convergence will increase
over Missouri ahead of this trough, so chances increasing to likely
and categorical by morning still look good.

Britt

&&

.SHORT TERM: (Through Sunday)
Issued at 304 PM CST Sat Feb 13 2016

Shortwave now over MT will drop southeastward into southwest IA
by 12Z Sunday. Low-mid level warm air advection will be increasing
over our area ahead of this feature. A strengthening southwesterly
low level jet over southwest MO will bring increasing low level
moisture into our area overnight. A band of snow is expected to
develop and extend into northeast MO and west central IL this
evening, then light snow will break out across the rest of the
forecast area late tonight. The greatest snow accumulation of up
to 1 inch should occur across northeast MO and west central IL
with a dusting elsewhere late tonight. The greatest snowfall
intensity and accumulation should occur Sunday morning as the
shortwave, vort max moves eastward through the MO IA border. Most
of the accumulating snowfall should shift east into IL and
southeast MO Sunday afternoon with most of the precipitation
ending across central MO. Total snow accumulations should range
from near 4 inches in Quincy and Mt. Sterling IL to around 2
inches in the St Louis metro area to around 1 inch in COU. The
forecast soundings were depicting an elevated warm layer in the
FAM area on Sunday which could lead to some sleet across parts of
southeast into central MO. As the moisture profile becomes more
shallow and the lift weakens there may also be some patchy
freezing drizzle late Sunday morning and afternoon across parts of
central and southeast MO. With forecast snow amounts increasing
slightly from the previous forecast, plus the inclusion of sleet
and freezing drizzle across parts of the area have expanded the
winter weather advisory to our entire forecast area for late
tonight and Sunday.

GKS

.LONG TERM: (Sunday Night through Next Saturday)
Issued at 304 PM CST Sat Feb 13 2016

The precipitation should shift east and southeast of our forecast
area Sunday night. Another shortwave will dive southeastward out
of the Plains and carve out an upper level trough over the
central US Monday. It appears that any measurable precipitation
will remain south-southeast of our forecast area. Temperatures
will be warmer on Monday allowing much of the snow to melt. A
northwest flow shortwave and associated weak surface low will drop
southeastward through the region late Monday night and Tuesday.
The NAM and GFS model move this feature through northern MO or
southern IA and central IL, while the ECMWF model is further
southwest with the track moving it southeastward through our
forecast area. There will be some potential for accumulating snow
across northeast MO and west central IL near and left of the track
of the upper level/surface low with mainly rain elsewhere with
warmer temperatures Monday night and Tuesday. Still looking
unseasonably warm for the end of the work week with upper level
ridging over the central US on Thursday along with strong south-
southwesterly low level flow.

GKS

&&

.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1100 PM CST Sat Feb 13 2016

Snow will develop overnight at all of the terminals with
visibilities and ceilings lowering to MVFR and then IFR. The snow
is expected to accumulate 1-3 inches at the terminals before it
ends from west to east, with KCOU seeing the least and KUIN seeing
the most. Still expect KCOU and the St. Louis area terminals to
see a transition to freezing drizzle with the possibility of a
light glazing of ice before ending by mid-late afternoon. The IFR
and MVFR ceilings will gradually improve by evening.

Specifics for KSTL: Expect snow to develop by 10Z with
accumulating snow through the morning hours before it transitions
to freezing drizzle by 18Z. Expect a snow accumulation around 2
inches with a light glaze of ice on top of it. MVFR and IFR
conditions can be expected during the snow and freezing drizzle
with improvement to VFR during the evening hours.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...Winter Weather Advisory until 6 PM CST Sunday FOR Audrain MO-
     Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Shelby MO-St. Charles MO-St.
     Francois MO-St. Louis City MO-St. Louis MO-Ste. Genevieve
     MO-Warren MO-Washington MO.

     Winter Weather Advisory until 6 PM CST Sunday FOR Knox MO-Lewis
     MO.

IL...Winter Weather Advisory until 6 PM CST Sunday FOR Bond IL-
     Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Randolph IL-St. Clair IL-Washington IL.

     Winter Weather Advisory until 6 PM CST Sunday FOR Adams IL-Brown
     IL-Pike IL.

&&

$$

WFO LSX


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