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Area forecast discussion
National Weather Service Lincoln Illinois
244 am CST Fri Dec 6 2019

issued at 244 am CST Fri Dec 6 2019

A few light showers are possible over southern Illinois this
morning, ahead of an advancing cold front. Behind the front, brisk
north winds and cooler temperatures will affect the area today.
For this weekend, dry weather and seasonably mild temperatures
are expected.


Short term...(today and tonight)
issued at 244 am CST Fri Dec 6 2019

Early morning surface map indicated 1012 mb low pressure over
central lower mi, with a cold front extending southwest into
west central Illinois. To the northwest, 1030 mb high pressure was
located over eastern South Dakota. A zone of gusty north winds up
to 30 mph was occurring in the tighter pressure gradient over Iowa.
Aloft, water vapor imagery and upper air analysis indicated a weak
shortwave trof from MO southwest into OK. Scattered showers were
occurring ahead of this feature from southern MO into southern Illinois.

These norther edge of the area of scattered showers could affect
areas south of I-70 this morning, and have maintained low chance
pops. Farther north, a band of Post- frontal strato-cu will shift
shift across the area this morning. Models are consistent in
showing rapid clearing from the northwest this afternoon, but have
slowed this trend given the extent of cloud cover to the north.
As the stronger cold air advection and tighter pressure gradient shift in from
the northwest this morning, north to northeast wind gusts up to 30
miles per hour are possible. Winds will gradually decrease this afternoon.
Highs should be 10-12 degrees cooler than yesterday, upper 30s
northwest to mid/upper 40s south of I-70.

Tonight, the surface ridge axis settles over the area 06-12z,
setting up good radiational cooling under light winds and clear
skies. Undercut lowest guidance by a degree or two for lows in the
low/mid 20s.


Long term...(saturday through thursday)
issued at 244 am CST Fri Dec 6 2019

The ridge axis begins to shift east of the area on Saturday,
allowing for dry and seasonable weather. Sunday, warm advection on
low to mid level southwest flow will push highs several degrees
above normal, mainly into the lower 50s.

The pattern turns more active for the Sunday night through Monday
night timeframe, when a longwave trof enters the central US. This
will develop low pressure over the Southern Plains Sunday night,
tracking northeast across Illinois Monday, and into the Great Lakes
Monday night. Given this track and the fact cold air lags the
surface system, this should primarily be a rain-maker. Some light
snow is possible Monday evening but accumulations are not
currently expected.

Modified Arctic high pressure building into the northern plains on
Tuesday, will bring a respectable shot of cold air to the region.
The high is forecast to shift overhead by early Thursday, keeping
the cold air around for a few days. Guidance shows the peak of the
cold air at 850 mb in the negative teens c on Wednesday which
would support highs in the low to mid 20s, after morning wind
chills in the single digits above and below zero.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1137 PM CST Thu Dec 5 2019

A cold front is pushing into northwest Illinois late this evening
and will continue to sag south across the central Illinois
terminals overnight. Southwest winds in place ahead of the front
will veer to the northwest and eventually north-northeast. Gusts
will pick up behind the front, initially in the low to mid 20 kt
range, but gradually easing through the day Friday. High pressure
will build overhead Friday night with winds quickly dropping off.
Meanwhile, mid level cloud deck is currently in place across
central Illinois and VFR conditions will persist until the front
passes. There should be a few hours of MVFR associated with a
stratus deck behind the front, but skies should quickly scatter
back to VFR Friday morning or early afternoon.


Ilx watches/warnings/advisories...


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