Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 050538

Area Forecast Discussion
National Weather Service Lincoln IL
1138 PM CST Mon Dec 4 2017

Issued at 856 PM CST Mon Dec 4 2017

A strong cold front has started to push into west-central and
northwest Illinois this evening. The front will rapidly sweep
through the state over the next few hours, exiting the state to
the east by shortly after midnight. A fairly narrow band of
showers and isolated thunderstorms precedes the front. The
thunderstorms have decreased in coverage significantly with the
loss of daytime heating, and this trend should persist. Southerly
winds have been gusting over 40 mph at times in some locations
this evening. Wind speeds/gusts should diminish a bit as the
front pushes into the area, but will swing around to the west and
increase again behind the front. Going forecast was in good shape
overall, but have made several adjustments to the hourly trends
for the rest of the night (especially PoPs).


.SHORT TERM...(This evening through Tuesday)
ISSUED AT 250 PM CST Mon Dec 4 2017

A cold front and band of showers/isolated storms will track across
the forecast area this evening. Forecast soundings continue to
exhibit low cape but strong shear in the 0-6km layer. Any of the
more organized showers and storms may be able to bring some of
those stronger winds down to the surface in isolated area early
this evening with some gusts up to around 50 mph. Once the band
of precip shifts east of our area, along with the cold front, late
this evening, winds will shift into the west which should start
the downward trend in temperatures for the rest of this week.
Gradient winds, which have gusted as high as 45 mph in a few
areas today, will stay rather gusty ahead of the front with a
lull in the stronger wind speeds after frontal passage later this
evening, with the stronger wind gusts returning on Tuesday as
deep cyclonic flow and low level cold air advection settles into
the region. We may see westerly winds gust up to 35 to 40 mph for
a time tomorrow as the deep storm system to our north slowly moves
away from central Illinois.

A rather large temperature gradient across the region tonight with
lows forecast to dip to the upper 20s north to the lower 40s far
southeast counties. Highs on Tuesday will rise into the upper 30s
far north to the low to mid 40s far south, but the gusty winds
will make it feel much colder than that.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 250 PM CST Mon Dec 4 2017

Much colder air settles over the region for this forecast period
as our upper flow transitions into the northwest thru at least the
first half of next week. A weak upper level wave will track across
our area on Wednesday bringing the possibility for scattered
sprinkles and flurries before a stronger wave dives southeast into
the Midwest late Friday into Friday night which may result in some
light snowfall across parts of the area. Once that late week wave
shifts off to our east by Saturday, another push of cold air settles
south across the forecast area for the rest of the weekend. Have
trended the forecast highs down from the initialization, which
appears to have been too warm again late in the period. Looks as
if though we may have a tough time getting out of the 20s across
the north with lower 30s expected over southeast IL.

Temperatures may moderate some on Sunday as the cold surface high
shifts off to our east with low pressure tracking well to our
north during the day. This will bring southerly winds back into
the region resulting in afternoon highs rising back into the upper
30s to lower 40s. Some light rain and snow chances return to the
area Monday into Monday night as the storm system and associated
cold front shift away from the region. As is the case with the
weather disturbances this week, the weekend system will not be a
major precipitation producer as there will be little in the way of
moisture to work with as the stronger dynamics remain to our north.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1136 PM CST Mon Dec 4 2017

Predominantly VFR condtions expected across the central Illinois
terminals through the 06Z TAF valid time. However, a few brief
periods of MVFR CIGS are possible over the next few hours. Gusty
westerly winds will persist for most of the period, with a
diminishing trend expected by Tuesday evening.




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