Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 010848
Area Forecast Discussion
National Weather Service Lincoln IL
248 AM CST Sun Dec 1 2013
ISSUED 248 AM CST Sun Dec 1 2013
Main forecast challenge focuses on departing storm system for the
middle and end of the week...and whether or not it will produce
any wintry precipitation across central Illinois.
SHORT TERM...Today through Tuesday
Weak cold front currently across northern Illinois will sink
southward today, eventually becoming stationary along the Ohio
River by evening. Front will be accompanied by little in the way
of sensible weather other than a shift in the wind. Low-level
moisture seen on IR/fog satellite across southeast Missouri/far
southern Illinois is progged by HRRR to remain mostly south of
I-70 today, while patchy mid-level clouds over Iowa into far
northern Illinois stay mostly north of the area. End result will
be mostly sunny skies until later this afternoon when clouds begin
to approach from the northwest. High temperatures will be bit
cooler behind the cold front, ranging from the middle 40s far
northwest around Galesburg to the lower 50s south of I-70.
Boundary will remain in place along the Ohio River through Monday,
before lifting back northward in response to rising upper-level
heights Monday night into Tuesday. Models continue to show a
subtle short-wave rippling eastward out of the Plains late Sunday
night into Monday that could interact with the front to produce
scattered light showers. Forecast soundings remain dry at
low-levels: however, think forcing will be strong enough to
mention a slight chance for showers on Monday. As front lifts
northward, rain chances will shift into the southern Great Lakes
on Tuesday. Brisk southerly winds south of the departing warm
front will bring much warmer air into the region, with Tuesday
afternoon highs reaching the lower to middle 50s.
LONG TERM...Wednesday through Saturday
Forecast becomes more challenging in the extended, as upper low
currently over northwest British Columbia drops southward and
carves a deep trough across the western CONUS by the middle of the
week. Downstream ridging will place the Midwest/Great Lakes in a
broad southwesterly flow pattern, leading to increased precip
chances Wednesday into Thursday. Models have been struggling with
the evolution of a surface low pressure system and its associated
cold front for the past several runs: however, the 00z DEC 1 run
seems to be coming into better agreement. While GFS remains a fast
outlier, the latest ECMWF has sped up the front quite a bit.
Following an ECMWF/GEM consensus yields FROPA across central
Illinois on Wednesday followed by sharply colder conditions for
the end of the week. Main question will be how much precip will
hold back in the colder airmass Thursday and possibly Friday.
Previous runs of the ECMWF had featured quite a bit of wintry
precip Thursday night into Friday as a secondary wave of low
pressure tracked along the departing front. While it still shows the
potential for wintry precip, it has backed off/shifted E/SE with
its latest solution. GEM seems to be the most consistent model
over the past couple of days, so have trended toward its solution.
With cold front passing on Wednesday, will mention a chance for
showers. After FROPA, precip will largely shut off Wednesday
night, before a wave of low pressure tracking from the lower
Mississippi River Valley into the Ohio River Valley brings a
renewed round of precip primarily across the eastern half of the
KILX CWA on Thursday/Thursday night. Have focused highest POPs
along/east of I-57 for both Thursday and Thursday night, tapering
down to just slight chances further west along/west of the
Illinois River. Precip type during the day Thursday will be rain
across the east, with a rain/snow mix along I-55 and mostly light
snow in the Illinois River Valley. As deeper layer of cold air
arrives, precip will change to light snow across the board
Thursday night, with a light accumulation possible. After that,
will hold on to low chance POPs for snow across the far E/SE on
Friday, although if trends continue, these may need to be dropped
entirely. Main weather story for the end of the week will be the
much colder conditions. Highs by Friday and Saturday will only be
in the 20s, with overnight lows in the single digits and teens.
ISSUED 1118 PM CST Sat Nov 30 2013
VFR conditions will prevail at all sites next 24hrs. Becoming
increasing obvious that light fog will not be developing
overnight. However, still thinking there is some lower level
moisture there and that some light fog still possible, but only as
a TEMPO group in the early morning hours from about 10-13z. Also
vis will not drop that much so TEMPO vis will be MVFR at 3-5SM.
Besides that, skies will be clear overnight and through tomorrow.
Then mid clouds around 12kft will advect into the area for the
evening hours. A weak front will move through the area overnight,
which should have winds switching to southwest and then west.
However, speeds are so light that variable direction is best
overnight. Then winds should be north to northwest after FROPA and
then become northeast during the evening hours.