Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 082102
AFDILX

AREA FORECAST DISCUSSION
National Weather Service Lincoln IL
302 PM CST MON FEB 8 2016

.SHORT TERM...(Tonight)
ISSUED AT 250 PM CST MON FEB 8 2016

Deep upper low centered over the Great Lakes will continue to
dominate the weather across central Illinois tonight.  Several
pieces of energy rotating around the parent low will bring periodic
snow showers to the area.  One wave evident on 20z/2pm water vapor
imagery over central Illinois is triggering wide-spread snow showers
across the KILX CWA.  However, weak synoptic subsidence in the wake
of this feature has led to a temporary lull in the precip further
upstream across eastern Iowa/southwest Wisconsin.  High-res models
suggest this lull will arrive across central Illinois this evening
before yet another subtle wave triggers additional snow showers
later tonight.  Snow accumulations will remain minor, with total
snowfall by early Tuesday morning of perhaps up to 1 inch.

&&

.LONG TERM...(Tuesday through Monday)
ISSUED AT 250 PM CST MON FEB 8 2016

Cold pattern to hold over the area through the forecast period
with the main challenge being timing of fast moving low amplitude
shortwaves embedded in the strong northwesterly flow and snow
chances associated with each later Wednesday, Friday and next
weekend. Powerful 200+ knot jet over the central Pacific this
morning will cause havoc with operational models with respect to
timing and magnitude of the low amplitude shortwaves that will top
the ridge over the western U.S. and then track southeast into the
mean longwave trof position over eastern NOAM. There are at least
3 of these waves we will have to contend with during this forecast
period.

Several weak shortwaves are still forecast to drop southeast along
the western periphery of the deep/cold 500 mb low that will be over
the region on Tuesday into early Wednesday. This will bring about
a continuation of the on and off snow showers across the area with
any additional accumulations of an inch or less. The big problem
will be with the gusty winds and cold temperatures during the day
with afternoon highs struggling into the upper teens northwest to
the middle 20s far southeast. The upper low will start to edge away
from the area Tuesday night into early Wednesday with the core of
the coldest air forecast to be over our area Wednesday with morning
wind chills of -5 to -15 with our coldest readings along and north
of the Interstage 74 corridor. Temperatures will be slow to recover
on Wednesday as afternoon temperatures are expected to top out in
the 15 to 20 degree range.

Models in better agreement with respect to a fast moving wave
forecast to track southeast into the area late Wednesday afternoon
and evening. A band of light snow will accompany the wave but
looking at forecast soundings sheds some doubt with respect to if
any precip will occur in our area, other than far west central IL,
as the shortwave is pushing right into the heart of the Arctic air
mass. However, this time of year, it doesn`t take much moisture or
lift to bring at least a brief period of light snow, especially to
the western counties late in the day and into the evening hours,
thus we will carry slight chance POPs during this time frame.
Once that wave shifts away from central Illinois late Wednesday
into Thursday, high pressure will dominate the weather keeping
below normal temperatures over the area until the next fast moving
clipper system approaches the area on Friday, at least according
to the latest ECMWF and GGEM models this morning, while the GFS
barely has much precip indicated around our area at that time.
With the GFS showing little if no precip in our area at this time,
guidance suggesting only slight chance POPs at this time and will
go with that for now. However, the ECMWF and GGEM models showing
another round of light snow for the area, which if it occurs,
will have a significant impact on temp forecasts for at least the
start of the weekend as another large Arctic high drops southeast
into the area. If there is a fresh covering of snow across central
Illinois, our temperature forecasts may be too warm. Something to
keep an eye on over the next several model runs.

The large Arctic high will dominate the area on Saturday but start
to shift away on Sunday as yet another shortwave drops southeast
into the mean longwave trof position, which will be slow to eject
away from our area. Precip chances will increase again as we head
into late Sunday and Monday of next week. Confidence on just how
amplified that trof will be and its affect on our thermal profile
and precip types that far out in time is quite low so will handle
with just 20 and 30 POPs for now. Temperatures will remain below
normal through the period with some adjustment upward next Monday
as the pattern starts to slowly deamplify, but we have been trying
that for several days now and models have pushed back with colder
solutions.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1203 PM CST MON FEB 8 2016

MVFR conditions will prevail through the entire 18z TAF
period...with occasional IFR visbys within heavier snow showers.
Models continue to suggest a break in the precip late this
afternoon and evening...and upstream obs across northeast
Iowa/southwest Wisconsin support this. As a result, have
temporarily ended snow showers after the 22z-00z time frame.
Another upper-level disturbance will pivot southward into the
region overnight, bringing a renewed round of snow showers. Based
on 12z NAM forecast, have brought precip back into the forecast
after 05z at KPIA...then after 09z further southeast at KCMI.
Winds will be strong/gusty from the northwest this
afternoon...gusting between 20 and 25kt at times. The gusts will
subside tonight...but sustained winds of 10 to 15kt will persist
through the night.


&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Smith
AVIATION...Barnes


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