Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 232048
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
248 PM CST Tue Dec 23 2014

.SHORT TERM...(Tonight)
ISSUED AT 247 PM CST TUE DEC 23 2014

Weak low pressure moving off to the NE out of Wisconsin this
afternoon as more cirrus spread over the region ahead of the next
system.  Deep troffing over the center of the CONUS part of the
development of the next sfc low to spread weather up into the
region, beginning as rain showers this evening and overnight.  Rain
will increase in coverage as well, spreading northward as the
surface low deepens.  Overnight lows will be moderate as cloud cover
will prevent a lot of radiational cooling, except in the NW that may
see a few holes in the clouds before the bulk of the cloud cover and
precip move northward. Forecast tonight rather calm by comparison to
the forecast for Wednesday with regards to track of the low and the
advancing storm.


&&

.LONG TERM...(Wednesday through Tuesday)
ISSUED AT 247 PM CST TUE DEC 23 2014

Plan to issue a Winter Weather Advisory for the central portion of
the forecast area, mainly between the Illinois River and I-57. This
advisory will cover the accumulating snow expected to develop
tomorrow, and persist into the evening hours. Confidence remains
lower than usual with respect to the exact details where the
heaviest snow will fall, and how high the accumulation may be.
However, considering the impacts when combining snowfall with a
busy travel day, decided to issue the headline to bring attention to
the snow potential. Later adjustments to the advisory remain a
distinct possibility.

The vertically stacked and decaying upper/surface low to our north
has done about all it is going to do to us precipitation wise, with
our attention now turning to the vigorous wave rounding the base of
the mean trof over the southern Plains. The surface low associated
with this wave will reach the vicinity of central Indiana or Ohio by
this time tomorrow, but there is still some appreciable spread in
the exact location within the models. The ultimate track will have a
significant impact on our forecast. Currently favor a solution
toward the western end of the model envelope which would place the
heavier snow within the deformation zone of the low across central
Illinois. The rain that initially accompanies the approaching
surface low should change over to snow fairly rapidly by midday
Wednesday. While some guidance suggests near surface temperatures
will remain warm enough for rain for much of the day, prefer the
more rapid cooling exhibited by the NAM given the potentially high
snowfall rates. Regarding the potentially high snowfall rates, the
models continue to support convective banding within the deformation
zone of this system. So, while we are currently forecasting 2-4
inches of snow with our currently favored track of the deformation
zone, the potential for locally higher amounts is certainly there.
The snow should rapidly taper off Wednesday evening as the system
pulls away.

In the wake of the Christmas Eve storm, Christmas Day and Friday
should be quiet and unseasonably mild as southerly low-level return
flow quickly develops. These warmer temperatures should help to
quickly melt the snow that falls tomorrow.

Further out, at least a couple waves may impact the area in the
Saturday-Monday time-frame. The waves will eject toward the region
from the southwest, and should mainly impact our southeast counties.
Thermal profiles support mainly rain ahead of the waves, with a
gradual trend toward snow as they depart. At this point, none of the
waves look like significant snow makers.


&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 1136 AM CST TUE DEC 23 2014
Not much in the way of changes in the shorter term TAF this
morning. Cirrus closing in the gap in the dry slot this morning
and mid level clouds anticipated by later this afternoon. Winds
becoming light and variable in the evening as MVFR clouds begin to
build back into the region from the SE as the next low pressure
system slides north into the area. Same low pressure system will
bring increasing chances for rain, eventually changing over to
snow mid morning. Timing is still low confidence, but needed to
start the trend. Should be all snow by noon in both SPI and PIA
and close to all snow in other terminals as well.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY from 9 AM to 9 PM CST Wednesday FOR
ILZ031-037-038-042>045-051>054-061.

&&

$$

SHORT TERM...HJS
LONG TERM...Bak
AVIATION...HJS





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