Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 211739

Area Forecast Discussion
National Weather Service Lincoln IL
1139 AM CST Tue Nov 21 2017

Issued at 1058 AM CST Tue Nov 21 2017

The cold front has been more active than yesterdays models were
indicating, with even some sleet reports coming in from NW
Illinois. While precip may be reaching the ground from time to
time as the cold front moves into Indiana around 6 pm, measurable
rain or melted precip will be isolated. Have included some
chance/slight chance PoPs for light precip with the front, and
included a ribbon of snow/sleet on the back edge of the precip
shield as it moves east. HRRR output continues to show the frontal
precip diminishing with time, but still has a few spotty showers
all the way through 6 pm in our far SE counties. Falling temps
still look on track for this afternoon behind the cold front,
especially for areas W of I-55. Clearing is projected to occur
relatively quickly behind the precip, so mostly clear skies and
chilly northwest winds look good as well.

Updated forecast info is already available.


.SHORT TERM...(Today and tonight)
ISSUED AT 250 AM CST Tue Nov 21 2017

08Z/2 am surface analysis shows 984 mb low pressure near Lake
Nipigon Canada (just north of Lake Superior) with its cold front
extending through central WI into eastern IA and nw MO. Breezy SSW
winds ahead of the cold front over central IL with winds gusting
to 20-30 mph. These breezy SSW winds along with some bands of
mid/high clouds keeping temps up tonight, currently ranging from
mid 30s in far southeast IL over Lawrence county, to the upper
40s over west central IL from Macomb to Pittsfield west. Aloft a
517 dm 500 mb low was nw of Lake Superior and embedded in a larger
upper level trof over the Midwest and extending southward across
the MS river valley.

00Z forecast models take low pressure eastward to the southern tip
of James Bay Canada by 18Z/noon today and into nw Quebec by 00Z/6
pm as it weakens to 990 mb. This will pivot the cold front se
across the heart of central IL by noon and pass the Wabash river
by late afternoon. Moisture still appears limited with frontal
boundary, though some short range models now showing some patches
over qpf over northern CWA this afternoon. Added slight chances of
light rain showers mainly ne of I-74 this afternoon. Highs today
range from mid 40s over the IL river valley, to mid 50s by
Lawrenceville. Brisk nw winds behind the cold front gusting 25-30
mph will drop temps to the lower 30s northern CWA by 6 pm and
40-45F in southeast IL, se of I-70.

1032 mb Canadian high pressure over central Alberta Canada will
settle into eastern KS overnight and ridge into IL by sunrise
Wed. This will decrease clouds and winds and bring a much colder
night tonight. Lows tonight will be in the lower 20s over central
IL and mid 20s in southeast IL. Could even dip into upper teens nw
of IL river over parts of Knox and Stark counties.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 250 AM CST Tue Nov 21 2017

High pressure ridges from Texas ne into the Ohio river valley at
sunset Wed and to bring lighter winds and ample sunshine but cold
temperatures. Highs 35-40F Wed with coldest readings from I-74 ne
and lows Wed night in the mid to upper 20s. High pressure settles
over the mid Atlantic states Thu while a weak cold front washes
out as it drops into northern IL during Thursday. Not quite as
cold on Thanksgiving day with highs in the mid to upper 40s.
Milder highs in the 50s on Friday with breezy SSW winds, similar
to yesterdays readings, with areas from Springfield sw approaching

Models take a 980 mb surface low pressure eastward across central
Ontario province Friday night and pushes another cold front se
across CWA. Have slight chances of light rain showers from I-74 ne
Friday evening. A deep upper level trof digs over the eastern
states during this weekend and brings in colder air back to the
area. Highs Sat range from mid 40s northern CWA to 50-55F southern
CWA, with temps likely slipping during the day. Highs Sunday only
in the upper 30s and lower 40s despite ample sunshine. Upper level
ridge builds over the Great Plains on Sunday night and Monday and
brings IL fair wx with moderating temperatures. Highs Monday in
the low to mid 40s, and in the upper 40s to mid 50s next Tuesday.
GFS and ECMWF models similar in taking low pressure eastward
across northern parts of ND/MN and Lake Superior Monday night/Tue
and brings a cold front thru central IL Tue afternoon/evening with
next chance of showers.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1139 AM CST Tue Nov 21 2017

VFR conditions will prevail through the 18Z TAF period, despite
the cold frontal passage this afternoon. The initially dry air
mass is limiting precip potential with the front, but some light
rain/sleet has been reported this morning. The HRRR does show the
frontal circulation weakening this afternoon, but until that
occurs, have added VCSH to all the TAFs for a few hours this
afternoon with FROPA. Clearing should develop quickly this
evening, if not late this afternoon NW of the IL river.

Winds have shifted to W-SW at 12g22kt, and a shift to NW will
occur post-FROPA. Wind speeds are slated to increase to 15g27kt
this afternoon from the NW. Winds will weaken this evening, and
remain light NW through the morning tomorrow under minimal cloud




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