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000
FXUS63 KILX 080831
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
231 AM CST Sun Dec 8 2013

.DISCUSSION...
ISSUED 230 AM CST Sun Dec 8 2013

Initial wave of precipitation approaching the southern CWA early
this morning, with light snow being reported over parts of the St
Louis metro and as close as Litchfield at 230 am. Dry air initially
keeping the leading edge of the precip aloft, but the column will
be moistening quickly as isentropic lift persists. Initial
forecast concerns will be with precip through this evening
including specific type. Further out, focus remains on duration of
this cold snap.


SHORT TERM...Today through Tuesday:

Initial precipitation expected to be all snow this morning, then
concern shifts toward potential for some freezing drizzle as the
ice crystals in the column erode from the top down. Have kept
mention of freezing drizzle over most of the area this afternoon
except the far north, where the transition is more likely early in
the evening. Forecast soundings from the far southeast CWA
indicate some sleet potential as well. Not really looking for any
substantial ice accumulation aside from a minor glaze. Snow-wise,
could see around an inch near Galesburg and Peoria, with a half
inch elsewhere west of I-55 and a dusting to the east. Most of the
precipitation should be out of the area by mid evening.

Digging shortwave over Utah early this morning will begin to
accelerate eastward Monday, with associated jet streak passing
through southern Missouri/Illinois Monday night and Tuesday
morning. Evening model runs starting to come into more agreement
with a quick shot of light snow in a narrow band along this
streak. Have added some 30% PoP`s across areas south of I-70 late
Monday night as a result. Any accumulation looks to be just a
tenth or two at this point.

Temperatures will continue to remain well below normal. Winds stay
up enough that wind chills will be approaching 10 below near
Galesburg late Monday night and Tuesday morning, with sub-zero
readings elsewhere north of I-72.


LONG TERM...Wednesday through Saturday:

One last southward surge of cold air expected mid-week, before the
upper pattern finally starts to shift a bit. Unfortunately the GFS
and ECMWF showing some spread in how much this pattern shifts late
in the week, with the GFS in a much milder pattern across the
CONUS and the ECMWF keeping the path of cold air continuing
through the Great Lakes. Have kept with the trend of above-
freezing temperatures by Friday. After that, made no changes to
slight chance PoP`s Friday night/Saturday, as both models show
some sort of precip but do not agree on the frontal configuration.


Geelhart

&&

.AVIATION...
ISSUED 1153 PM CST Sat Dec 7 2013

An initial wave of isentropic lift will work to saturate the low
to mid levels, but little in the way of snow accumulation is
expected from now through around mid-day Sunday. Flurries may
begin as early as 12z for SPI/DEC with mid morning flurries for
the remainder of the TAF sites. Some light accumulation of a few
tenths to near one half inch will be possible across a majority of
central and eastern IL. As much as one inch could accumulate
northwest of Peoria, but the higher totals of an inch or more
should remain mainly in Iowa and far NW IL.

The 00z models continue to show a split in the focus zones for
precipitation generation, with central IL in a coll zone between
jet dynamics to the southeast and the surface low to the
northwest. Overall, precip type could become mixed phase, with
freezing drizzle possible later Sunday into Sunday evening as we
lose ice crystals aloft but remain below freezing through the
lowest 5k ft of the boundary layer. Lift will be diminishing
during that time, as dry air progressively erodes the low level
moisture from aloft. Precip chances should come to an end before
midnight/06z Sunday night as the low pulls away to the northeast.

Winds will start out northeast the rest of tonight, then become
southeast as low level moisture increases. Some gusts to 20kt will
be seen as mixing depth increases. Weaker winds will return Sunday
evening as winds become due south by 06z Sunday night.

Shimon

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$