Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 192055

Area Forecast Discussion
255 PM CST Wed Nov 19 2014

.SHORT TERM...(Tonight)

Breezy and cold weather will be the rule across central Illinois
tonight.  19z/1pm surface analysis shows cold front exiting into
Indiana, while ridge of high pressure builds into the Plains.
Pressure gradient between these two features will continue to create
W/NW wind gusts of 25 to 35 mph this afternoon.  Gustiness will
begin to subside toward sunset: however, with ridge axis staying
west of Illinois until Thursday, gradient will remain tight enough
to support winds of around 10 mph through the night.  Clouds and a
few flurries will prevail early in the evening, with the big weather
question being how fast skies will clear later tonight.  Widespread
cloud cover is currently evident on satellite imagery from Illinois
northwestward to the US/Canada border: however, several holes in the
overcast have developed upstream across the Dakotas/Minnesota.  All
model guidance suggests clouds will begin to scatter this evening,
with mostly clear conditions expected overnight.  Given current
satellite imagery and continued deep northwesterly flow, think this
is too fast.  Have therefore gone with a slower clearing trend more
in line with the HRRR solution.  End result will be cloudy skies
this evening, followed by gradual clearing overnight.  Due to the
clouds and continued breeze, have gone with the higher end of
numeric guidance for lows tonight, with readings ranging from 14
degrees in Galesburg to around 20 degrees south of I-70.


.LONG TERM...(Thursday through Wednesday)

Moisture channel satellite imagery and the morning upper air shows
deep upper level trof over eastern US with main jet from central
Canada into the midwest. This upper flow will bring in another surge
of cold air, with cold surface high moving into region during the
day Thursday and Thursday night. With clear skies by Thursday night,
have lowered Friday morning lows some due to light winds and cold

Main precipitation concern is for Friday evening and Friday night,
as overrunning precipitation develops from AR into MO ahead of
digging shortwave in the southwest US. Precipitation will reach
central IL Friday evening, so temperature forecast will be critical,
as warm air aloft will produce precipitation in form of rain.

A detailed look at the model surface temperature forecasts depicts
EUR warmest, GFS, and NAM coolest. Feel the warming temperatures
will be blend of GFs and NAM, as conditions will start off cooler
Friday morning, as lowered morning lows. Feel current forecast grids
a good compromise and so looks like pcpn will start in evening
Friday as light freezing rain, with the freezing line gradually
moving to the northeast overnight. Pcpn amounts still look to be
light, so impacts will be on the light scale.

Saturday pcpn will be rain, as overrunning pcpn continues to develop
and move into the region. Strongest dynamics look to be on Sunday,
as the shortwave system and surface low approach and move through

Models are similar in the movement of system, with low center
tracking just west of the cwa Sunday, with front moving through area
and gusty winds. Vertical stacking of the upper low over Lake MI on
sunday night.

Cool conditions will conditions into midweek, as the upper low
gradually moves off and allows another cool high pressure area into
the midwest.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)

Cold front has pushed east of the central Illinois terminals late
this morning, resulting in strong W/NW winds across the board.
Based on 12z forecast soundings and the latest upstream
observations, wind gusts will generally remain in the 25 to 30kt
range before gradually subsiding toward sunset. Even though winds
will drop off tonight, pressure gradient will remain tight enough
to support sustained winds of around 10kt through the entire
night. 17z/11am satellite imagery shows low cloud cover spilling
into central Illinois behind the departing front, with the leading
edge currently approaching the I-57 corridor. A narrow band of
MVFR ceilings are noted across the Illinois River Valley, but
these should gradually rise to VFR over the next couple of hours.
Have therefore included MVFR conditions at KPIA/KBMI/KSPI through
20/21z. After that, the big question will be how fast skies clear
tonight. Due to ample upstream cloud cover within the
northwesterly flow pattern, have trended toward the more
pessimistic HRRR solution. End result will be a slow clearing
trend after dark, with ceilings scattering out at KSPI by 03z and
further northeast at KCMI by around 06z.




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