Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 020849

Area Forecast Discussion
249 AM CST Mon Mar 2 2015

.SHORT TERM...(Today)

High pressure centered from north central Missouri through northwest
Iowa will drift over the area today bringing a quiet weather scene
to the forecast area. Satellite data continues to show quite a bit
of cirrus streaking east over central Illinois with forecast
soundings and time height cross sections suggesting this will
continue through today bringing most areas filtered sunshine. MAV
guid appears to be a bit too warm with highs today considering the
fresh snow cover encompassing the entire CWA, with the NAM MOS
numbers a bit more reasonable. Will tend to follow the cooler guid
today with little to no low level warm advection expected until
the high shifts further off to the east, which won`t be until


.LONG TERM...(Tonight through Sunday)

Main forecast concern remains with the precipitation trends into
Wednesday, especially the ice potential tonight and early Tuesday.

Significant warm air advection to take place as a shortwave
currently along the Alberta/Saskatchewan border digs southward, as
the southern branch of the jet strengthens over the southern Plains.
The various models show temperatures in the 2,000-10,000 foot layer
rising as high as +4 to +7C by sunrise, but all are largely keeping
the lowest layer below freezing through the night. The column
remains dry below 800 mb through the evening, but will rapidly
moisten after midnight, so will quickly ramp up the PoP`s overnight.
Precipitation should largely be freezing rain, with some sleet/snow
mixed in primarily north of I-72. A winter weather advisory will be
required at some point, but have held off for now after coordinating
with surrounding offices. The main concern is that there is lower
confidence on how fast the freezing line will advance northward, as
a rather sizable area has some fresh and deep snow cover. Will issue
a Special Weather Statement instead, and an advisory can be issued
later this morning if the 12Z model runs have not made any
significant changes. Ice accumulations currently look to be around a
tenth inch in areas from Galesburg-Bloomington, and around .05" or
so south toward I-72.

The transition to plain rain will take place Tuesday morning,
advancing from southwest-northeast across the forecast area. The
precipitation will diminish as a cold front sweeps through during
the evening, but its progress will slow overnight as it becomes
parallel to the upper flow from the Ohio Valley southwest into
northern Texas. Surface waves will ride along the boundary, with
most of the models (except the GFS) spreading some light precip as
far north as the I-70 corridor on Wednesday. By that point, the
current upper wave to our northwest will dig a significant broad
trough across the northern Plains and send another slug of
unseasonably cold air into the Midwest, so any precipitation would
be in the form of snow. Initial thoughts are for an inch or two
south of I-70, with heavier totals across southern Illinois into the
Ohio Valley.

The aforementioned cold air mass will result in temperatures about
25-30 degrees below normal for Wednesday into early Friday, before
some rapid moderation takes place late week. The strength of the
warm up will depend on how much of the snow pack manages to melt on
Tuesday, but areas from I-72 southeast to Effingham-Hutsonville
currently have near a foot on the ground, so some snow cover should
still linger into late week.


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

Thin high cirrus will remain over all TAF sites overnight and into
early tomorrow morning. Then models showing mid clouds around
10-12kft advecting into the area and covering all TAF sites during
the around noon. These mid clouds look to hang around through the
afternoon and into the evening hours. Based on Bufkit data, clouds
should lower just ahead of the pcpn expected to arrive in west
central Illinois after midnight tomorrow night, which appears to
be just after TAF valid time. Winds will be westerly overnight and
then become light and variable tomorrow through tomorrow night.




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