Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 252040

Area Forecast Discussion
240 PM CST Sun Jan 25 2015

.SHORT TERM...(Tonight)

Area of low pressure which has brought our precipitation was
centered near Carbondale early this afternoon. Rain/snow transition
line has been struggling to move any further south, and in fact
areas from Macomb to Bloomington which had switched over were
starting to mix with rain again. Temperatures have been above
freezing over most of the snow area and accumulations have been
minor and slushy, but some more substantial 1-2 inch totals have
occurred north of Galesburg where temperatures are now below
freezing. The deformation band of snow has been weakening some the
last few hours, and there is a substantial hole in the precip over
the central 2/3 of the forecast area.

The RAP model shows a further weakening of the the deformation band
over the next few hours, and actually has the entire CWA dry by 6
pm. Have some concerns that may be too quick across the southeast,
as the upper wave continues to dig across southeast Missouri, and
have lingered some likely PoP`s down there slightly beyond that time
frame, but reduced PoP`s to below 20% by 9 pm.

Overnight, models are trying to show some substantial clearing over
most of the forecast area beginning late evening. While there is
some breakup of the clouds upstream across Wisconsin, it is not
completely clear up there and the north/northeast flow is not
especially conducive to rapid clearing. Have gone with partly cloudy
skies overnight across the northwest half of the forecast area, but
clouds will already been increasing ahead of the next clipper which
will be dropping southeast into northern Minnesota overnight.


.LONG TERM...(Monday through Sunday)

A couple of cooler days are on tap across central and southeast
Illinois in the wake of today`s clipper. There is still a chance we
may see a few snow flakes or sprinkles on Monday as a shearing
upper-level wave, currently diving across the Canadian Prairies,
passes through the Great Lakes region and parts of the Midwest.
However, looking at forecast soundings, there will be a very small
window of opportunity where ice crystals will be present, suggesting
the chance of measurable precipitation is quite low. So, for now,
will only carry a chance of flurries Monday across the northern
portion of the forecast area as the very sheared wave passes to our
north. It is definitely possible that we will see nothing at all, or
perhaps some light drizzle or freezing drizzle (depending on surface
temperatures) due to the paucity of ice crystals.

Temperatures will warm heading into midweek as the persistent
amplified upper-level flow briefly turns more zonal, and a system
approaches from the Pacific coast. This system will mainly pose a
rain threat as it moves through Wednesday night into Thursday. A
brief period of snow is not out of the question later Thursday as
cold air filters in behind the system, but forecast soundings
currently suggest the moisture depth will be too shallow to support
precipitation (no ice crystals) by the time the thermal profile
would support snow.

Another cool down is expected in the wake of the midweek system, but
temperatures should still be near normal for late January. The
eastern North American mean trof that has been in place will try to
reestablish itself by the weekend. A clipper type wave in the
returning northwest upper-level flow may bring a chance of snow to
the area over the weekend. However, the current storm track keeps
the best snow chances to our north, and have only included a slight
chance of snow at this time.


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

Several challenges with this TAF set. Widespread precipitation
north of a KIJX-KDNV line has been changing from rain to snow.
Radar data indicates the transition line is just south of KBMI to
about 30SW KPIA, although a bit of mixed precipitation has also
been reported near KCMI. Still seeing temperatures in the upper
30s to lower 40s from KSPI-KCMI so the transition is still a
couple hours away. High-resolution model data suggests some
erosion in the precip shield as the afternoon goes on, as a
surface low travels through the southern tip of the state, so most
of the TAF sites should see the precip end by 00Z. Strong
northeast winds kicking in on the north flank of the low
circulation, so winds 25-30 knots will be spreading over the TAF
sites over the next couple hours and persist much of the evening.
IFR/LIFR conditions will be occurring as the snow moves through.
Some improvement expected this evening, but have largely kept MVFR
ceilings at all TAF sites through the night, as the wind flow does
not favor rapid clearing. Did scatter out KPIA for a time after
06Z, as suggested by a narrow clear slot on the RAP model. Winds
to turn more southwesterly Monday morning ahead of a storm system
which will pass to our north.




SHORT TERM...Geelhart
AVIATION...Geelhart is the U.S. government's official web portal to all federal, state and local government web resources and services.