Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 280905

Area Forecast Discussion
305 AM CST Sun Dec 28 2014

.SHORT TERM...(Today)

Main short-term challenge will be timing of the clearing trend
today. 08z/2am IR satellite imagery shows low clouds covering much
of central Illinois, except across the far northern KILX CWA from
Peoria northward where clouds have eroded. The 06z NAM 1000-850mb RH
field has a good handle on the current cloud cover, so have
generally followed its solution for sky cover today.  End result
will be clearing skies along the I-74 corridor by mid to late
morning, with clouds lingering into the afternoon further south.
Skies will become mostly clear across the board by late afternoon as
high pressure builds in from the west.  High temperatures will be
near normal for this time of year in the middle to upper 30s.


.LONG TERM...(Tonight through Saturday)

Quiet weather is expected for the next several days before a storm
system gradually approaches from the southwest by the end of the
week.  High pressure will control the weather across central
Illinois on Monday, resulting in cool/dry conditions with highs in
the 30s. Meanwhile, a significant chunk of cold air currently in
place across central/western Canada will sink southward into the
central CONUS by the middle of the week.  Models have been hinting
at some light snow/flurries as CAA increases Monday night into
Tuesday, with the NAM being more aggressive with potential QPF.  NAM
time-height cross-sections reveal stronger lift within a deeper
moist layer than the GFS indicates.  Think the low-level moisture
may be a bit overdone on the NAM, so am leaning toward the GFS
solution here.  Even with drier air below 850mb, think lift will be
strong enough to warrant mention of a few flurries Monday night and
perhaps even into Tuesday morning before moisture profile thins and
high pressure builds into the region.  Heart of the cold airmass
will arrive Tuesday night into Wednesday, when overnight lows dip
into the single digits and teens and highs only reach the lower to
middle 20s.

Once high slowly begins to shift eastward, attention turns to a
developing southern-stream storm system associated with a cut-off
upper low over the Desert Southwest.  Models are still displaying
a typical spread of solutions that far out, but confidence is
growing that a precipitation event will impact central Illinois by
the end of the week.  Both the GFS and ECMWF show surface low
pressure developing over the Texas panhandle by Friday evening, then
lifting northeastward into the Great Lakes on Saturday.  While their
tracks are not in perfect agreement, a N/NW trend is becoming
apparent.  GFS takes the low west of the CWA to near Moline by 12z
Sat, while the ECMWF tracks the low to near Champaign.  Both tracks
are further N/NW than previous runs, which suggests precip may be
more in the form of rain or a rain/snow mix across the area than
previously thought.  Based on GFS forecast soundings, if precip is
able to spread northward into the initially cold/dry airmass Friday
morning, light snow will be the primary precip type.  As temps warm
into the middle to upper 30s, the snow will likely mix with rain
across much of the area by Friday afternoon.  Precip will likely
remain quite light during the day Friday, with widespread precip
holding off until Friday night when airmass saturates and stronger
lift arrives.  At this point, will carry rain along/south of
I-70...a rain/snow mix across the middle of the CWA...and snow
along/north of a Rushville to Bloomington line Friday night into
Saturday.  The track of the system will likely change with
successive model runs, so precip type and any potential snow
accumulations still remain uncertain.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)

Precip has shifted east of all the terminal sites, and MVFR clouds
will blanket the area the rest of the night and through much of
the morning tomorrow. CMI has a brief break in the MVFR clouds
until 07z/1am, but low clouds will fill in by 07z. The back edge
of the clouds is positioned to our west from south-central
Wisconsin through SE Iowa and down through the middle of Missouri.
The clearing progression has slowed later this evening, and that
trend should allow low clouds to linger over the terminal sites
into tomorrow morning. PIA should be the first to clear out,
possibly as early as 12-13z. Clearing trends should speed up with
turbulent mixing of dry air tomorrow, reaching BMI by 14z, SPI by
16z, CMI by 18z and DEC by 19z. The HRRR is quicker with clearing,
as is the RAP. Will stick with a more pessimistic clearing trend
until satellite images give more confidence in the models cloud
progressions. Wind speeds will decrease below 10kt by 08z-09z
tonight, and remain less than 10kt through the day tomorrow. Wind
direction will start out NW, then back to the west during the day
as high pressure builds farther into Illinois.




LONG TERM...Barnes
AVIATION...Shimon is the U.S. government's official web portal to all federal, state and local government web resources and services.