Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 022057
Area Forecast Discussion
National Weather Service Lincoln IL
257 PM CST Mon Dec 2 2013
ISSUED 257 PM CST Mon Dec 2 2013
A slow moving area of low pressure continues to get organized over
the northern Plains, with a warm front extending southeast along
the Missouri/Illinois border. The front will lift through the
forecast area by Tuesday, reinforcing our recent trend of days
with above normal temperatures. However, once the cold front with
this system arrives by late Wednesday, sharply colder conditions
will be with us for the foreseeable future. Main forecast concerns
today revolve around the speed of arrival of the approaching
system`s cold front, as well as the local thermal
profile/precipitation type for later Thursday into Friday as a
strong disturbance rides northeast along the front (which will
have stalled south of the Ohio River by that time).
There continues to be model disagreement with respect to the
approach/passage of the cold front for midweek. The synoptic U.S
models continue to be the quickest (front coming through during
day Wednesday, while the ECMWF/Canadian are several hours slower
(front coming through Wednesday night). Both model camps have had
at least a few runs of consistency between them. The faster speed
of the U.S. models is driven by a chunk of energy in the
developing western U.S. trof shunting along the northern tier of
states and developing a stronger surface low with it. The slower
solutions keep most of the energy in the mean trof and only give
the plains low a gradual push east. Have shaded forecast toward
the faster solutions, although confidence in the ultimate outcome
is still low.
SHORT TERM...Tonight through Friday: Mostly cloudy and mild
conditions are expected across the region into Wednesday, with
predominantly southerly low level flow in place and favorable
moisture parameters for cloud development/persistence.
While a few sprinkles can not be ruled out tonight or early
Tuesday as the warm front lifts north, significant rainfall is
not expected. The arctic cold front for Wednesday is also not
expected to be a significant rain producer due to the shallow
moisture depth associated with it. Wednesday night and into
Thursday, as the cold air spills into the area behind the front,
the precipitation appears likely to shut off before the vertical
profile cools enough to support snow.
The front is expected to become parallel to upper level flow by
early Thursday, stalling south of the Ohio River Valley. Then, a
140+ kt jet streak and accompanying wave will track along the
frontal boundary, triggering a widespread area of precipitation.
The heaviest precipitation should fall south of the forecast area,
closer to the stalled front, but most of the forecast area should
see some precipitation.
Across most of the forecast area, the thermal profile supports all
snow, but areas along/south of the I-70 corridor have a better
chance for mixed precipitation. Surface temperatures will be
critical in determining if any of the liquid rainfall freezes, but
there is not enough confidence to pin point the threat just yet.
If a majority of the precipitation in our southeast counties falls
as snow with the frontal wave, a few inches of accumulation is
LONG TERM...Saturday through Monday: Quiet and colder than normal
conditions will be in place to start the weekend, but another wave
is expected to eject out of the mean western U.S. trof by Sunday.
This wave will bring another chance of snow to the area. At this
point, any accumulation with this next system appears minor. Well
below normal temperatures should be the rule through the period,
and no significant warm up is evident, even beyond this forecast
ISSUED 1125 AM CST Mon Dec 2 2013
MVFR visibilities expected to persist much of the TAF period.
Clouds so far have been around 8000 feet or so, but should migrate
downward to around 3500 feet after sunset as an upper disturbance
approaches from the northwest. Have maintained some VCSH at
KPIA/KBMI this afternoon as the disturbance passes, but any rain
should be light and not last long. Forecast soundings showing
ceilings falling later in the night and will likely be below 3000
feet in many places by early morning.