Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 310543

Area Forecast Discussion
1143 PM CST Fri Jan 30 2015


High pressure is dominating the weather across central Illinois
this evening, providing clear skies and calm winds. Radiational
cooling beneath the high has led to a quick temperature drop, with
some locations seeing a 5-6 degree fall between 6pm and 7pm. As
the high shifts eastward later tonight, a light southerly return
flow will develop which will mitigate the rapid cooling. Have adjusted
hourly temps and lowered overnight lows into the teens across the
far north around Lacon. Elsewhere lows will bottom out in the
lower to middle 20s.


.SHORT TERM...(Tonight)

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.


.LONG TERM...(Saturday through Friday)

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)

VFR conditions will prevail through Saturday morning as high
pressure gradually shifts east of the region. Clouds will begin to
thicken/lower by afternoon in advance of an approaching storm
system. All model guidance brings light rain into the area between
19z and 21z, with forecast soundings suggesting ceilings lowering
into the MVFR category at that time. As profiles moisten/cool
further, a rain/snow mix will develop at the terminals prior to
06z.  Have reduced visbys and lowered ceilings to IFR accordingly.


WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.



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