Winter Weather Advisory 2, NWS Lincoln, IL

Area Forecast Discussion
National Weather Service Lincoln IL
338 AM CST Sat Jan 4 2014

.DISCUSSION...
ISSUED 300 AM CST Sat Jan 4 2014
Central Illinois between systems this morning as a high pressure
ridge stretches out over the Atlantic coast...and several waves
make their way over the Rockies in the west. Low center currently
over the Oklahoma panhandle will be a contributor to the next
winter storm for the region. Overall, the models have been fairly
consistent with producing high snowfall totals and brutal cold on
the back side of this system. Forecast is adjusting details and
keeping an eye on the trends. Conflicts about spread of greatest
snowfall, as there will likely be a sharp gradient on the NW side
of the snow track, one of the concerns. But abundant moisture
through the column and very cold temperatures with sustained lift
in the region resulting in a major snow event for the weekend.

SHORT TERM...Today and tomorrow...
Snow. Frontogenetic forcing starting to develop and spread across
the CWA this afternoon will bring snowfall starting NW of the
Illinois River before sunset. Snow will continue through the
overnight, picking up intensity after midnight with the heavier
snowfall totals east of the Interstate 55 corridor after midnight.
At this point snow starts to intensify as the addition of the
jet influence aloft adds into the dynamics. The surface system
moves through and pulls out to the east, resulting in major snow
fall particularly along and south of Interstate 70. Open wave
aloft providing no isentropic lift...dynamics are confined to jet
and frontogenetic forcing. But the column is saturated and PW
values for several 6 hr pds in the .3 -.5 range. Prolonged
snowfall with that much water resulting in 6-12 inches of snow
through Sunday night for areas south and east of the Illinois
River Valley. Heaviest snowfall in the region btwn the Interstate
70 corridor and the Ohio River Valley. Whereas the snowfall NW of
the Interstate 55 corridor to the Illinois River Valley may be
more borderline with regards to the Winter Storm Warning criteria
within allotted time, impacts between the snowfall and the blowing
snow is enough to expand the Warning area to include up to the
river. Winds becoming gusty and ramping up to 15-25 mph sustained
on Sunday afternoon and gusting in excess of 30, particularly in
the east Sunday night as the sfc system winds up and pressure
gradient increases. WSW timing through at least 06z should cover
the worst portion of the blowing snow and high winds. Temperatures
Sunday night plummeting into the negative teens as brutally cold
air is pushed into the region behind the exiting storm.

LONG TERM...Monday through Friday...
Choosing not to complicate the WSW with the wind chill, but bears
mentioning that the CWA will likely see headlines again with the
wind chill should the trends continue. With the winds Sunday night
continuing...and the highs on Monday well below zero...wind chill
values will head to -30 to -40 after 06z and Monday morning will
be brutally cold...and this cold will continue through Tuesday
morning. Tuesday highs and Tues night lows both in single digits
before a slight warm up on Wednesday to the 20s. However, that
warm up is in advance of the next system moving out of the SW
along a more zonal pattern that results in another swath of
precip/snow along the Ohio River Valley... continuing the snowy
pattern. The remaining forecast is mostly an AllBlend
forecast...with a trend to ConsRaw as a result of the highly non
climatological pattern.

HJS
&&

.AVIATION...
ISSUED 1133 PM CST Fri Jan 3 2014

VFR conditions will prevail at the start at all sites overnight
and into the morning hours, as clear skies continue. Then high
cirrus will move into the area with broken cigs at 20kft. Lower
clouds do not arrive until after the light snow begins in the
afternoon. First thought is it will start around mid afternoon at
PIA and then slowly move eastward through the afternoon. Vis will
start as 3sm but then lower to 1 1/2sm as the snow increases for
the evening hours. Cigs will also fall to below 1kft during the
evening. Snowfall will increase after midnight, which is just
beyond this forecast period. Winds will remain gusty overnight and
then begin to taper during the morning hours as the gradient
loosens. Winds will continue to decrease in speed as the front
moves into the area during the afternoon, actually becoming
variable at PIA/BMI and SPI. Since gusts to around 30kts is
occurring at the sfc, have decided to remove mention of LLWS.
However, strong winds of 50-60kts are being observed by the radar
at 1.5-2.5kft overnight.

Auten
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from this evening through Sunday evening FOR
ILZ038-042>046-048>057-061>063-066>068-071>073.

&&

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