Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 240931

Area Forecast Discussion
331 AM CST Wed Dec 24 2014

.SHORT TERM...(Today)

Latest surface analysis indicating the storm system of interest for
us was located over northwest Alabama and is now forecast to track
further east than earlier thought and should be in extreme eastern
Indiana or western Ohio by this afternoon. This will push the
band of heavier precip east as well which would suggest the
accumulating snow will set up east of I-55, more like along and east
of I-57 for any significant accumulations. Forecast soundings off just
about any model you look at was indicating boundary layer temperatures
still too warm to support any long duration of accumulating snow
until this afternoon or early this evening over extreme east central
Illinois. Even in these locations, wet bulb zero heights were above
1200 feet, so we will need to see some significant forcing associated
with the shortwave trof/upper low to produce some dynamic cooling that
may be able to overcome the warm boundary layer temperatures. Not
seeing any strong trends back to that solution with the past couple
of model runs, as a result, have started to trim back on the advisory
across our west for now. Have added some counties across extreme east
central Illinois due the eastward shift to the storm track and where
the better and longer duration lift will set up this afternoon and
early this evening. As far as snowfall is concerned, very low end
advisory snowfall totals across the area with generally 1 to 3 inches
east of I-55, and if model trends continue to shift the surface low
track further east, the better setup for accumulating snow will be
east of I-57.


.LONG TERM...(Tonight through Wednesday)

Snow to diminish from west to east during the evening with around
a half inch of additional snow from 6-9 pm from Champaign and
Paris northeast. Surface low pressure deepens nne to 988 mb at 6 pm
near Detroit and to 980 mb near Georgian Bay Canada by midnight
tonight. Blustery west winds 15 to 20 mph and gusts of 20 to 30 mph
this afternoon/evening to gradually diminish late tonight as deep
low pressure pushes into western Quebec by dawn Thu/Christmas morning.
Low stratus clouds to gradually decrease from sw to ne during day
on Thu with surface ridging into IL from southeast states. Above
normal highs in the lower 40s on Thu. This should melt most of the
snow by Thu afternoon. Even milder highs of 45-50F on Friday as
breezy ssw winds develop, with clouds increasing especially by Fri

Models have been trending slower on low pressure ejecting ne from
CO into the western Great Lakes by dawn Sat and pulling a cold
front se through IL Sat. Have chance of light rain Friday night,
though may hold off in eastern/se IL until overnight Friday night.
Then have light rain changing to light snow Sat over central IL
with mix over southeast IL. Any snow accumulations look fairly
light with this system over central IL. Highs Sat range from mid
to upper 30s over IL river valley to mid to upper 40s in southeast
IL. Cooler highs in the 30s on Sunday across region behind the
cold front which pushes into KY/TN. Models differ with
disturbances tracking ne along the frontal boundary and stuck
close with superblend pops this weekend, with highest pops in
southeast IL. Appears cold enough for mainly light snow chances by
Sunday and Sunday night in southeast IL. Temps to cool further
behind system early next week with below normal temps expected by
middle of next week.


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

Models are coming into better agreement on shifting the bands of
snow farther east into eastern IL, and away from being centered on
the I-55 corridor. The overall trends are showing less
accumulating snowfall for areas along I-55 and more toward I-57
and east. The NAM is still indicating a band of 1-2 inches from BMI
to DEC with 2-3" from CMI and east to the Indiana border. The
change to snow still looks on track for sometime during the
morning due to to an eastward shift in the track and a better
chance that cold air will be drawn farther east during the
morning. Will remove the tempos for LIFR conditions during
moderate to heavy snow, and will prevail IFR during snows tomorrow
afternoon. Snow will diminish or end by early evening, with mainly
flurries lingering into evening for the I-74 corridor.

Have trended from VFR at the start of the TAF period down to MVFR
clouds between 07z-10z, then dropping to IFR clouds and MVFR vis as
the rain-snow transition begins tomorrow morning. Continued IFR
conditions after the rain completely changes to snow later tomorrow
morning into afternoon. Lift conditions to MVFR clouds in the evening.

Some NW wind gusts could climb to 18-20kt early in the afternoon,
then diminish to less than 10kt by evening.


WINTER WEATHER ADVISORY from 9 AM this morning to 9 PM CST this
evening FOR ILZ038-043>046-052>057-061.



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