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000
FXUS63 KILX 051107
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
507 AM CST Thu Dec 5 2013

.DISCUSSION...
ISSUED 253 AM CST Thu Dec 5 2013

Approaching winter storm continues to be the primary concern
with this forecast package. Accumulating snow is expected across
the E/SE KILX CWA later today through Friday.

SHORT TERM...Today through Saturday

Strong cold front has pushed east of the Illinois/Indiana border
early this morning, allowing a rapid drop in temperatures across
the area. 08z/2am readings have already slipped into the upper 20s
along/west of the Illinois River, but remain in the upper 40s in
the Wabash River Valley. Temperatures will continue to drop over
the next couple of hours, then will remain nearly steady for the
remainder of the day. Afternoon temps will range from the upper
20s west to around 40 degrees far southeast.

Wave of low pressure will develop along the departing cold front
and track northeastward into the Ohio River Valley later today.
Models have made some minor changes from their previous
forecasts, mainly to bring precip into the SE CWA faster today and
to sharpen up the northwest edge of the precip shield tonight and
Friday. Thermal profiles remain virtually unchanged, with a warm
layer aloft supporting mixed phase precip along and south of a Paris
to Shelbyville line this afternoon/evening. Should see a
rain/sleet mix develop initially, before transitioning to all snow
by mid-evening. Further south, a brief period of freezing rain is
likely along/south of highway 50 early this evening before
sleet/snow mix develops toward midnight. As deeper layer of cold
air arrives, precip will change to all snow overnight. Wintry
precip will mainly be confined to locations along and south of a
Jacksonville to Rantoul line, with areas further northwest only
seeing a few flurries.

A second wave of low pressure will track along the front on
Friday, bringing a renewed round of precip to the E/SE CWA.
Airmass will be cold enough to support all snow, with precip
gradually diminishing/shifting east by afternoon. Total snowfall
accumulations from this afternoon through Friday afternoon will be
heaviest south of I-70, where 4 to 7 inches will be likely. As a
result, will be issuing a Winter Storm Warning for Crawford,
Jasper, Clay, Richland, and Lawrence Counties. Further north, 2 to
4 inches of snow will fall along and south of a Paris to
Shelbyville line, where a Winter Weather Advisory will be in
effect. North of there, totals of around 1 inch are anticipated
along a Danville to Taylorville line.

Once the system departs the region, cold and dry weather will be
on tap for Friday night and Saturday, with overnight lows dropping
into the single digits and highs only reaching the lower to middle 20s.

LONG TERM...Sunday through Wednesday

Short-wave is progged to drop southward out of Canada this
weekend, carving out an upper trough over the western CONUS.
Downstream ridging will allow front that is currently pushing east
and south of Illinois to nudge back northward. While models are
still in disagreement as to how much moisture will return
northward, both the ECMWF and GEM have been suggesting that
boundary and deepest moisture will remain further southeast over
the Tennessee and Ohio River Valleys on Sunday. Meanwhile,
approaching western CONUS trough will have much less moisture
associated with it and should generally lift E/NE toward the Upper
Midwest/Great Lakes. End result will be cloudy skies with a period
of light snow across central Illinois Sunday afternoon and night.
A minor accumulation will be possible, but it is still too early
to tell exactly how much. Once the trough arrives, much colder
conditions will take hold early next week, with highs struggling
to rise through the teens by Tuesday.

&&

.AVIATION...
ISSUED 500 AM CST Thu Dec 5 2013

An Arctic air mass will continue to spread southeast into the
region today bringing in drier air at the low levels...which will
result in a decrease in MVFR cigs this morning from west to east.
Latest satellite and surface obs to our west support this thinking
this morning as we are seeing MVFR cigs slowly decreasing as the
very dry air mass advects southeast into our area. Will continue
from the previous forecast in bringing in mainly VFR conditions
starting out west from 15z-17z...and into the east by 19z. However,
forecast soundings and time height cross sections show quite a bit
of mid level moisture/clouds streaming northeast into our area
during the day ahead of the weather system expected to produce
some significant snows to the south of the taf sites tonight and
Friday. Will probably see VFR cigs lower to around 4000 feet at
DEC and SPI this evening, and from 6000-8000 feet further north.
Will include a VCSH in SPI and DEC this evening as they will be
close to the northern edge of the precip shield to the south.
Surface winds will be from the northwest at 10 to 15 kts today
with a few gusts to around 20 kts, with northwest winds around
10 kts tonight.

Smith
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 6 PM this evening to 6 PM CST Friday
FOR ILZ067-068-071>073.

WINTER WEATHER ADVISORY from 6 PM this evening to 6 PM CST
Friday FOR ILZ056-057-061>063-066.

&&

$$