Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 210854
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
254 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 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
60F.

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 06Z TAFS through 06Z Tuesday night)
Issued at 1125 PM CST Mon Nov 20 2017

VFR conditions are forecast to remain across the area through
this forecast period. The main forecast challenge will be with
the low level winds late tonight into early Tuesday. Forecast
soundings continue to show the low level jet will be centered over
our area into the overnight hours with winds at 1200-2000 feet
AGL in the 40-50 kt range with a gradual decrease in speeds after
09z as the core of stronger winds shifts to our northeast and a
cold front approaches the TAF area from the west. Despite some
occasional gusts at the surface there is still enough of a spread
in wind speed from the surface to around 2k feet to keep the LLWS
going into the early morning hours.

Mid level moisture/clouds will increase tomorrow morning ahead of
a cold front that will shift across the area into the early
afternoon hours. Surface winds will be south to southwest at 12-17
kts during the morning and then shift into the northwest at 12-20
kts after FROPA with CMI the last to see the winds shift into the
northwest at around 19z. Wind gusts up to 20 kts possible
tomorrow afternoon after the FROPA, but should diminish out of the
northwest by evening with speeds of 10 kts or less.

&&

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

&&

$$

SHORT TERM...07
LONG TERM...07
AVIATION...Smith



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