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000
FXUS63 KILX 032056
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
256 PM CST Tue Dec 3 2013

.DISCUSSION...
ISSUED 256 PM CST Tue Dec 3 2013

A mild but rather foggy day continues across central and southeast
Illinois today due to a warm front lifting through the area
earlier today. The foggy conditions have slowly improved from
south to north as the front lifted toward the IL/WI border. One
more mild day is expected on Wednesday before the cold front
associated with a slow moving Plains system moves through the
region. Now that the model disagreement with cold frontal timing
has been resolved, primary forecast concerns revolve around
precipitation chances/types with the passage of the cold front and
as additional waves develop along the front once it stalls south
of the Ohio river by Thursday/Friday.

Model agreement is finally good with the speed of the approaching
cold front, with the front expected to be about half way across
the forecast area by 00Z Thursday and east of the area by 06Z
Thursday. There are still model differences with timing/track of
waves expected to ride northeast along the cold front once it
stalls well south of the forecast area later Thursday. Plan to
follow the ECMWF solution most closely in this regard as it has
been most consistent, and it is also a more middle of the road
solution.

SHORT TERM...Tonight through Friday: Main concern tonight is
whether or not dense fog will redevelop. This is certainly a
possibility given the low level moisture trapped beneath a strong
low level inversion, as well as the surface dew point temperatures
remaining well above near surface soil temperatures. However,
would expect the highest risk of dense fog to occur to our north
in the vicinity of the warm front. So, for now, plan to carry
areas of fog for tonight, but will not reissue an advisory.
Visibility trends will need to be watched closely to see if this
thinking needs to be adjusted.

Only modest forcing and shallow moisture will be available for the
approaching arctic front to work with Wednesday into Wednesday
night as it moves through the forecast area. This supports keeping
our current low chances of rain going. With the later arrival of
the front, Wednesday should be the warmest day of the week, with
many areas reaching 60 degrees or higher. However, if the cloud
cover is thick enough, as it has been today, temperatures may not
get as warm as they otherwise could.

Wednesday night/early Thursday should be mostly dry behind the
front, and the precipitation will have shut off before the
vertical thermal profile cools enough to support anything other
than rain. The first of a couple short waves, coupled with a 150+
kt upper level jet, will arrive later Thursday afternoon into
Thursday night. A second wave will move through on Friday. At this
point, it looks as though the heaviest precipitation with these
waves (at least in our forecast area; heavier totals are likely
south of our area) should fall south of a Shelby county to Edgar
county line, with the greatest chance of mixed precipitation
occurring along/south of the I-70 corridor. The bulk of the models
have trended a little cooler in the vertical as these waves are
expected to move through the area, a fact that appears to be
shifting the higher risk of icing farther south of the forecast
area. Still, model spread exists and additional shifts are likely
in the favored area for icing and/or heavier snow. While no winter
weather headlines are warranted at this time, forecast trends
should be monitored closely, especially across southeast Illinois.

LONG TERM...Saturday through Tuesday: Unseasonably cold conditions
are expected through the extended range of the forecast, with most
days averaging 15-20 degrees below normal. Another wave is still
progged to eject out of the mean western U.S trof, providing a
risk of snow from Sunday into Sunday night. At this point, the
expected snow accumulation with this system look minor.

Bak
&&

.AVIATION...
ISSUED 1128 AM CST Tue Dec 3 2013

The area of lowest visibilities from dense fog has been
contracting inward the last hour or so, and most TAF sites are now
up past 1SM except near KPIA/KBMI, which should come up soon.
Forecast soundings show ceilings should creep upward to around
1000-1500 feet this afternoon, but then drop back into IFR range
this evening as the inversion around 1500 feet holds tight.
Forecast challenge is whether or not the dense fog will return as
well. Visibility guidance from the RAP/HRRR models indicate the
period near/after 06Z would be most vulnerable for dense fog. Will
start it around 06Z in the upcoming TAF set, but monitor closely
for signs of it starting earlier in the evening. Visibilities
should increase Wednesday morning ahead of a strong cold front,
which will sweep across the TAF sites after 18Z.

Geelhart
&&

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

$$