Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 111606
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1006 AM CST Thu Jan 11 2018

.UPDATE...
Issued at 1006 AM CST Thu Jan 11 2018

16z/10am surface analysis shows a strong cold front approaching
the Mississippi River. Ahead of the front, southerly winds
continue to transport unseasonably warm/moist air into central
Illinois this morning...with current temps in the middle to upper
50s. Meanwhile behind the boundary, readings rapidly drop into
the upper 20s and lower 30s across eastern Iowa. Based on morning
trends, it appears the front may be an hour or two faster than
previously forecast. Satellite timing tools and latest HRRR
suggest it will reach the I-55 corridor by 20-21z...then clearing
the far SE KILX CWA by 01-02z. Given continued southerly flow for
much of the day, have raised highs into the lower to middle 60s
east of I-55. Have also adjusted hourly temp to better reflect
expected trends. Readings will fall into the upper 20s and lower
30s west of I-55 by late afternoon...with any lingering rain
showers changing to a period of freezing rain. Precip will then
transition to freezing rain and snow across the remainder of the
CWA tonight...before coming to an end from west to east overnight.
Due to residual water freezing on road surfaces, as well as minor
ice and snow accumulations, the current Winter Weather Advisory
will remain in effect through late tonight into early Friday
morning.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 254 AM CST Thu Jan 11 2018

Temperatures were in the mid 50s across most of the forecast area
early this morning, courtesy of southerly winds which have been
gusting from 25 to 40 mph at times. Not much in the way of rain
over the area as of 2:30 am, but radar mosaics are starting to
show some light development over central Illinois, with more
widespread rain further west.

The cold front was moving into central Iowa per latest surface
analysis. Short-range models project it to reach Galesburg and
Peoria around 1-2 pm, I-55 toward 4pm and I-57 around 6 pm. No
changes in the general thinking of precipitation types, with a
warm layer around 850 mb favoring a period of freezing rain and
sleet behind the front. An additional surge of moisture will
impact the southeast half of the forecast area, prolonging the
mixture into early Friday morning. The bulk of the accumulations
will be in this area, with potential for ice accumulations of
.05-.15 inches and 1-2 inches of snow.

Will issue a Winter Weather Advisory from 6 pm tonight to 6 am
Friday for areas from about I-55 east. Further west, an advisory
will run from 3 pm to midnight. While QPF and associated icing is
low there, concerns are two-fold. First, forecast soundings hint
at potential for some light freezing drizzle to linger for a few
hours after frontal passage. Secondly, the scope of the
temperature fall (30-40 degrees in a few hours) suggest a flash
freeze of the wet pavement before winds get a chance to dry it
off, resulting in some icy conditions.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 254 AM CST Thu Jan 11 2018

Remainder of the forecast will be dominated by the return of the
Arctic air masses. Highs tomorrow will be 35-40 degrees colder
than today, and will edge downward from there. Worst of the cold
air will follow passage of a clipper system on Monday, with a
warming trend setting up just beyond the current forecast period.

Aside from the residual precipitation from the current system
early Friday, the aforementioned clipper is the only real
precipitation threat of consequence in this period. GFS and ECMWF
models are in very good agreement with a quick shot of snow Sunday
night and Monday morning, likely an inch or two. A large upper low
will settle into the Great Lakes behind it, and may result in some
fast moving, flurry-producing troughs rotating around it. However,
due to some differences between where exactly this is centered,
will hold off on any additional mention.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 523 AM CST Thu Jan 11 2018

Ceilings starting to lift a bit and become more in the MVFR range
over central Illinois, though they hover around 800 feet from
about KDEC-KCMI. The strongest winds from overnight have settled a
bit, but southerly gusts of 25 knots or so are still on tap much
of the day. A strong cold front will reach KPIA around 20Z and
KCMI by 23Z, resulting in winds quickly switching to the
northwest. Any rain occurring with this front will become a
freezing rain and sleet mixture for a few hours post front. KCMI
is most likely to see this linger past 06Z. Late in the period,
ceilings should lift above 3,000 feet from west to east.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to 6 AM CST
Friday for ILZ038-042>046-051>057-061>063-066>068-071>073.

Winter Weather Advisory from 3 PM this afternoon to midnight CST
tonight for ILZ027>031-036-037-040-041-047>050.

&&

$$

UPDATE...Barnes
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart



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