Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 261801

Area Forecast Discussion
1201 PM CST Thu Feb 26 2015


Updated the forecast at mid morning for ending of the winter
weather advisory over parts of central IL. Light snow will
diminish to flurries late this morning and afternoon with less
than a half inch of additional snow se of the IL river.
Temperatures currently near highs today ranging from near 15F nw
of IL river to mid 20s in southeast IL. North winds 10-20 mph will
cause temperatures to slowly fall this afternoon with some blowing
snow in open rural areas. Alberta clipper system will exit se of
IL today with light snow diminishing this afternoon. Some clearing
of low clouds nw of IL river by Knox, Stark and Schuyler counties.
But another short wave moving se toward IL this afternoon to
likely keep low clouds around rest of today over most of central
and southeast IL.


.SHORT TERM...(Today)

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


.LONG TERM...(Tonight through Wednesday)

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.





LONG TERM...Barnes
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