Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 241758
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1158 AM CST Fri Feb 24 2017

.UPDATE...
Issued at 1045 AM CST Fri Feb 24 2017
Cold front is draped across Central Illinois this morning, just
passing through ILX. Winds coming around to more westerly behind
the boundary, and much cooler air. Out ahead of the boundary,
south/southwesterly winds still ushering warm humid air for this
afternoons storm development. So far, shower development has been
spotty and well ahead of the front. Expecting main initiation
later today, potentially near I-57, depending on the progress of
the boundary. SPC has pushed the slight risk in the day one
outlook to the east this morning...and the marginal risk is edging
over to the IL/IN border. MUCAPE on the ILX sounding this morning
was only 316 J/kg, but with the rapid heating in eastern IL, the
forecast CAPE should be closer to over 1000 J/kg...and SPC
Mesoanalysis is already getting to that point closer to CMI. Minor
updates to the forecast out momentarily.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 320 AM CST Fri Feb 24 2017

08z/2am surface analysis shows 995mb low over northeast
Missouri, with warm front extending from near Quincy to just south
of Kankakee.  This places all but the far NW KILX CWA within the
warm sector of the system as is evidenced by widespread temperatures
in the upper 50s and lower 60s.  Locations from Peoria northward are
north of the warm front and are therefore still hovering in the
lower to middle 40s.  The low is projected to track slowly N/NE
today...reaching north-central Illinois by 18z...then southwest
Michigan by 00z.  The timing of the low and its associated trailing
cold front is right on target from previous forecasts, so the main
short-term challenge remains timing of convective initialization
along/ahead of the boundary.  Aside from a stray shower or
thunderstorm this morning, it appears the most widespread
precipitation will hold off until afternoon as the front pushes into
east-central Illinois.  Strong southerly winds gusting to 30-35mph
ahead of the front will push temperatures into the upper 60s and
lower 70s.  With dewpoints climbing well into the 50s, this will
result in MUCAPE values of around 1000J/kg.  As a strong mid-level
jet streak approaches from the west, 0-6km bulk shear will climb to
60-70kt this afternoon.  This marginally unstable/highly sheared
environment will be conducive to scattered strong to severe
thunderstorms with potentially damaging wind gusts along and east of
the I-57 corridor between 1pm and 6pm.  There will also be a minimal
tornado risk as cells first begin to develop...but it appears the
higher probabilities for tornadoes will be focused further east
across Indiana.

Any storms that fire this afternoon will quickly push into Indiana
by early this evening, followed by windy and sharply colder
conditions.  Models continue to suggest the trailing upper wave will
trigger a period of light snow late tonight.  Based on track of
500mb wave, it appears the snow chances will remain north of the
I-70 corridor.  Due to the light nature of the precipitation and
the very warm ground conditions, am not expecting much in the way
of accumulation.  Some locations near the track of the upper
disturbance northwest of the Illinois River around Galesburg may
pick up as much as one half inch, but little to no accumulation is
expected elsewhere.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 320 AM CST Fri Feb 24 2017

Light snow will end across north-central Illinois Saturday morning
as the wave tracks into the Great Lakes.  It will be a brisk and
chilly day in its wake however, with high temperatures only in the
30s and wind-chill readings in the teens and 20s.  As high pressure
builds into the region, clearing skies and diminishing winds will
lead to cold lows in the lower to middle 20s Saturday night.

The return to winter-like conditions will be short-lived, as zonal
flow allows temperatures to quickly moderate early next week.  A
series of short-waves will also bring unsettled weather at times,
with the first wave arriving Sunday afternoon/evening.  Temperatures
during the day Sunday will climb into the middle to upper 40s, so
the precip Sunday afternoon will be in the form of light rain.  If
the precip lingers long enough into Sunday night, there may be a
brief change over to light snow as temperatures drop into the lower
to middle 30s...however no accumulation is expected.  A lull in the
precip chances will noted on Monday, as temperatures climb even
higher into the lower to middle 50s.

After that, a stronger short-wave trough crossing the Rockies will
lead to cyclogenesis across the Plains and the arrival of a more
significant frontal boundary by mid-week.  Timing differences still
exist between the ECMWF and GFS: however, it appears low pressure
will track N/NW of Illinois and the trailing front will pass late
Tuesday.  With unseasonably warm temperatures in the upper 50s and
lower 60s, GFS is showing MUCAPE values of 400-600J/kg Tuesday
afternoon and evening, warranting a slight chance for thunder. Once
the front passes, a return to cooler readings in the 40s is
anticipated for Wednesday and Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1143 AM CST Fri Feb 24 2017

A cold front moving through the area and by 18z, winds should be
out of the west and gusty behind the front... south/southwesterly
ahead of it, still in CMI for at least another hour until the
front moves through. Stratus expected to dominate the TAF pd,
mainly in the MVFR category. Bringing down the cigs behind the
front and pretty much staying down overnight with scattered snow
showers anticipated. Not enough confidence on timing or location
of individual showers, so no reduction in the forecast for now.
Also may be light enough not to warrant too much of a concern.
Winds slowly becoming more northwesterly by morning, but will
remain gusty due to the increased pressure gradient.

&&

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

$$

UPDATE...HJS
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...HJS



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