Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 200305
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
905 PM CST Wed Nov 19 2014

.UPDATE...
ISSUED AT 900 PM CST WED NOV 19 2014

Flurries continue to affect much of central IL this evening under
a weak shortwave in the strong W-NW flow. A band of low clouds
associated with the feature will persist the rest of the evening
and most likely well after midnight before dry air above the cloud
layer creates some clearing. Satellite images show breaks in the
clouds upstream, so periods of clearing should progress across the
area later tonight. That clearing and some decrease in wind speeds
should help low temps dip to forecast numbers in the mid-upper
teens by sunrise Thursday. W-NW winds of 8-12 mph will push wind
chill readings down into the single digits after midnight.

High pressure will advance east into IL on Thursday, providing
mostly clear skies and continued cold conditions. However, winds
should be lighter under the ridge axis and weaker pressure gradient.

Updates this evening were mainly to the sky grids to match
expected trends. We kept clouds around longer after midnight, but
still expect clearing for tomorrow morning. Updated info is
already available.

&&

.SHORT TERM...(Tonight)
ISSUED AT 254 PM CST WED NOV 19 2014

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)
ISSUED AT 254 PM CST WED NOV 19 2014

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
airmass.

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
region.

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 00Z TAFS through 00Z Thursday evening)
ISSUED AT 559 PM CST WED NOV 19 2014

Strong W/NW winds will highlight the early TAF forecast as gusts
to 30kt still showing up from PIA to BMI. Pressure rises of 2-3mb
per 3-hours will continue through around 3z/9pm behind the cold
front, so will continue gusts at all terminal sites through that
time. After that, pressure rises slow down, but a continued
pressure gradient across the NE half of IL will help keep
sustained winds in the 12-15kt range for at least the northern
terminals of PIA/BMI/CMI.

2330z/530pm satellite imagery shows breaks in the low cloud cover
upstream across Iowa and S MN, but a channel of clouds from W Iowa
back into SD/ND streaming toward SPI and DEC. Forecast soundings
are generally pessimistic with cloud cover through the night, but
still expect some clearing to develop later tonight. Most cloud
cover will be VFR anyway, so the clearing will not be a major
change in flight category. However, ceilings are hovering right
around 3k ft near PIA/BMI, so a brief period of MVFR cloud heights
can not be ruled out there.

Once the skies clear out, we expect enough dry air mixing tomorrow
to prevent any BKN cloud decks from forming, but moisture will
remain in the 2-3k ft layer according to forecast moisture
profiles. Winds will be less gusty than today, but sustained winds
will climb back into the 12-15kt range through the day from the west.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Goetsch
AVIATION...Shimon





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