Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 282110
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
310 PM CST Sun Dec 28 2014

.SHORT TERM...(Tonight)
ISSUED AT 310 PM CST SUN DEC 28 2014

High pressure briefly building into the region this evening as
clouds slowly erode and move off to the southeast.  Colder air
moving in with clearing skies tonight will drop overnight lows a few
more degrees from last nights lows.  With the ridge axis moving into
the region, the winds become light and variable in the overnight,
allowing for more efficient radiational cooling in addition to the
colder airmass.  Other than the cold start to the morning, weather
tonight rather quiet for the Midwest.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 310 PM CST SUN DEC 28 2014

As the high pressure shifts to the southeast, a larger, colder high
pressure area will slide in with Arctic air. There will be a thin
boundary between the two air masses and with this, there will be a
small chance of flurries as it passes. Timing of this feature looks
to be Monday night and Tuesday morning. This colder Arctic high will
bring well below normal temps to the region for Tue night through
Wed night. The coldest lows are expected to be Tue night and the
coldest highs on Wed. Breezy northwest winds during the period will
also create wind chills below zero across the northern part of the
state, especially Tue night and Wed morning.

This high pressure will dominate the weather through Thur night and
will slide into the eastern US by Thur evening. With this high to
the east and an upper level low in the southwest US, moisture and
warmer temps will begin to advect back northward into the region.
Model differ on the timing of this return flow and this results in
differences in timing of the return of pcpn to the area. The ECMWF
is quicker and further east with the track of a low pressure area,
along with the associated pcpn. The GFS is slower and further west
to northwest with the track, and thereby brings more warm air into
the region ahead of the low pressure area, and more pcpn. Looks like
the regional blend leans toward the GFS with a western track, more
warm air ahead of the system and more of a spread of pcpn over the
area. The next question then, is what will p-type be during the
period. Due to the spread of the models, confidence is low, so will
keep p-type simple and just go with snow becoming rain or snow, and
then just rain, and then back to rain or snow. 850mb temps look to
be couple of degrees above freezing, so would expect rain well north
into the cwa. However, the question is the sfc temps. Anywhere with
temps below freezing has the potential of receiving freezing rain.
But if the rain is heavy enough, then temps could remain at or just
above freezing overnight Friday. To repeat, forecast confidence is
low due to model spread, so will not be adding any freezing pcpn at
this time. As the system gets closer and the models reach some
agreement and consistency, forecast changes are likely. Beyond this
system, dry and cooler temps are again expected for Sat night and
Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1150 AM CST SUN DEC 28 2014
Thick cirrus making it difficult to discern location and trend in
low stratus. So far, SPI and DEC between VFR and MVFR with the
stratus deck just under 2kft. Will maintain the trend at least
through the end of the day. Beyond sunset, expect a retreat of the
stratus, but will need to watch...and cirrus through the rest of
the fcst. Light NW winds becoming light and variable as the ridge
axis moves over ILX terminals later tonight.

&&

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

$$

SHORT TERM...HJS
LONG TERM...Auten
AVIATION...HJS





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