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Area forecast discussion
National Weather Service Lincoln Illinois
550 am CST Tue Nov 21 2017

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 Iowa and NW MO. Breezy south-southwest
winds ahead of the cold front over central Illinois with winds gusting
to 20-30 mph. These breezy south-southwest winds along with some bands of
mid/high clouds keeping temps up tonight, currently ranging from
mid 30s in far southeast Illinois over Lawrence County, to the upper
40s over west central Illinois 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 Illinois 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 County Warning Area this afternoon. Added slight chances of
light rain showers mainly NE of I-74 this afternoon. Highs today
range from mid 40s over the Illinois 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 County Warning Area 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 Kansas overnight and ridge into Illinois 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
Illinois and mid 20s in southeast Illinois. Could even dip into upper teens NW
of Illinois 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 Illinois 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 south-southwest 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 County Warning Area. 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 County Warning Area 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 Illinois 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 European model (ecmwf) models similar in taking low pressure eastward
across northern parts of ND/Minnesota and Lake Superior Monday night/Tue
and brings a cold front thru central Illinois Tue afternoon/evening with
next chance of showers.


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 545 am CST Tue Nov 21 2017

VFR conditions expected to continue across the central Illinois airports
through 12z/6 am Wed. 985 mb low pressure near Hearst Canada
between James Bay and Lake Superior, has a cold front near the
Iowa/Illinois border. This front will sweep southeast to the Illinois River by
15z/9 am, and reach Dec and cmi about 18z/noon. Low level wind shear will occur a
couple more hours across central Illinois airports with 1-1.5k ft west-southwest
winds of 35-40 kts. South-southwest winds 10-15 kts early this morning will
veer west-southwest by mid morning, then shift northwest behind the cold front
between 15-18z and gusts 18-25 kts into the afternoon. Northwest winds
diminish to 6-10 kts early this evening as 1033 mb high pressure
along the southern Alberta and Saskatchewan province line settles
into the Central Plains overnight. Broken to overcast mid level
clouds 8-12k ft will push se to Illinois River early this morning and
during mid/late morning at Dec and cmi. Ceilings could get as low
as 4-5k ft this afternoon especially along I-74 where isolated
light rain showers possible, but too isolated in nature to mention
in the tafs.


Ilx watches/warnings/advisories...


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