Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 250912
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
312 AM CST Tue Nov 25 2014

.SHORT TERM...(Today)
ISSUED AT 312 AM CST TUE NOV 25 2014

Low pressure that brought widespread rain to central Illinois on
Sunday is now over Quebec, with trailing cold front approaching the
East Coast.  Despite the parent low being so far away from the
region, lingering upper troughing is keeping cloud cover locked in
place.  08z/2am IR satellite imagery shows low clouds covering all
of central/northern Illinois and as far west as eastern Iowa.
Timing tools are indicating only a very slow eastward progression of
the clearing line, so have delayed the clearing across the KILX CWA
accordingly. The day will start out overcast across the board, then
a slow west-to-east clearing will occur as the day progresses.
Based on latest satellite loop and 00z forecast soundings, think
locations along/northeast of a Bloomington to Mattoon line will
remain cloudy for the entire day.  Further west and south, skies
will become partly to mostly sunny this afternoon.  Will be a cold
day with highs only in the 30s, but it will not be nearly as windy
as yesterday with westerly winds generally around 10 mph.


&&

.LONG TERM...(Tonight through Monday)
ISSUED AT 312 AM CST TUE NOV 25 2014

Main weather challenge in the extended continues to be clipper
system expected to track through the region on Wednesday.  00z Nov
25 models are in excellent agreement with the timing and track of
the system, but display minor differences with their QPF fields.
All models take low pressure currently over Alberta and track it
southeastward into western Iowa by 12z Wed, then into southern
Illinois by 00z Thu. This represents a continued southerly trend
in the track, which means portions of the far N/NE CWA may see
little or no precip with this system.  NAM is the most
concentrated with its QPF, keeping it confined very near the low
track.  Meanwhile, both the GFS and ECMWF are more generous and
spread light precip further north across the entire area.  Have
updated Wednesday precip chances to focus likely PoPs along/south
of a Rushville to Decatur to Robinson line, tapering down to low
chance northeast of I-74.  Given the more southerly track, WAA
ahead of the wave will be weaker than previously thought, so high
temps will not be quite as warm.  Afternoon readings will range
from the middle 30s far north to the lower 40s south of I-70.
Forecast soundings support snow: however, surface temps will be
warm enough for a rain/snow mix across much of the area and
perhaps mainly rain across the far southeast.  Snowfall amounts
will be mitigated by the marginal temps and overall light QPF,
with perhaps a half inch along/southwest of Macomb to Springfield
line where the precip will begin during the morning hours when it
is still cold enough to support all snow reaching the ground.
System will quickly track into the Appalachians Wednesday night,
with just a few lingering snow-showers across the E/SE into the
evening.

Once Wednesday clipper departs, the remainder of the extended
appears to be quiet.  A shot of cold air behind the system will drop
high temps into the upper 20s/lower 30s on Thursday: however, a
marked warming trend is still expected for the end of the week as
eastern CONUS upper troughing relaxes and a zonal pattern develops.
As southerly winds develop on the back side of departing high
pressure, high temperatures will soar well into the 50s on Saturday
before a cold front sags southward into the region late in the day.
Still some discrepancies further out concerning how far south front
will make it, with overall consensus taking it into the Ohio River
Valley by Sunday.  High pressure initially along the Gulf Coast will
limit northward moisture return, so showers will likely not develop
along/ahead of the boundary until it sinks into the SE CWA Sunday
afternoon/night.  All model solutions point to a cool/dry day on
Monday before southerly flow resumes and precip chances slowly begin
to increase by Tuesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
ISSUED AT 1138 PM CST MON NOV 24 2014

One more meso-vortex on radar is poised to rotate from far eastern
Iowa across northern Illinois over the next few hours. The primary
precip type appears to be light snow, but patchy freezing drizzle
could still develop due to localized lack of ice crystals above
the cloud layer. Snow was the only precip type included in the
TAFs for PIA and BMI, the closest to the wave. All precip should
end before sunrise on Tuesday, with dry conditions the remainder
of the TAF period.

MVFR clouds will linger until mid-morning for the southern
terminals of SPI/DEC, and possibly into the afternoon for the
northern terminals. Clearing will develop by sunset.

Winds will remain a bit gusty for the first 3 hours of this TAF
period, with gusts near 20kt at times. Gusts will subside by
sunrise, with sustained winds tomorrow generally less than 10 kt
from the west.

A band of
mixed freezing drizzle and snow moved across our northern
terminals over the last couple of hours, and additional bands of
mixed precip could affect the same areas through 03z. Numerous
accidents have been reported on many roads including I-74 near
Galesburg and I-39 from El Paso and north to Tonica.

MVFR clouds will likely hold steady over the next 24 hours, with
precipitation generally coming to an end by 06z.

Very gusty winds will continue through at least mid-evening. Gusts
should end by 06z, but sustained winds will likely remain in the
12-15kt range in most areas overnight. PIA and SPI could see the
pressure gradient weaken enough for wind speeds to drop below 10
kt before sunrise Tuesday. Cloud heights will lift to VFR Tuesday
morning after sunrise and mixing increases.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Shimon






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