Area Forecast Discussion
Issued by NWS Central Illinois

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861
FXUS63 KILX 041723
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1123 AM CST Sun Dec 4 2016

.UPDATE...
Issued at 952 AM CST Sun Dec 4 2016

Precipitation shield has spread over most areas north of I-70 this
morning, with scattered rain showers to the south. Dual-pol radar
products indicating the transition zone between snow and rain/mix
is just north of I-72 from around Springfield to Champaign.
Earlier mixed precipitation around Jacksonville and Pittsfield has
switched back to snow per radar and surface obs. RAP/HRRR precip
type imagery showing mostly snow through the afternoon north of a
Jacksonville-Paris line and mostly rain to the south, but
temperatures will creep up a degree or two and updated grids
continue with the rain/snow mix spreading as far north as Havana.
Accumulation-wise, surface reports have indicated 1.5 to 2 inches
across parts of Knox and Stark Counties so far, and totals over
the far northern CWA still expected to be in the 3-4 inch range,
with around an inch or less near I-72. No changes to the headlines
at this time.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 401 AM CST Sun Dec 4 2016

Precip is slowly advecting into western IL early this morning and
most precip is in the form of rain, with snow reports back in Iowa.
Expecting precip to increase across the area this morning with
mainly snow in the north and a mix of rain and snow along and south
of the I-72/Danville corridor and then all rain in southeast IL.
With cloudy and precip across the area today, not expecting temps to
increase much, if at all; therefore, not expecting much in the way
of p-type changing through the day. Snowfall totals from this event
could reach 2-3 inches in the northern third of the CWA, with over 3
inches possible north of I-74. However, with the ground temps in the
mid 30s and air temps being in the mid 30s, believe accumulations
could be less and conditions could end up being more slushy than
snow covered. So, main accumulations will likely be on grassy areas,
elevated surfaces and vehicles.

Precip will push east during the afternoon and there could be some
lingering precip in northeast IL early this evening, but will end
quickly, with the remainder of the night being dry.

Temps should be fairly steady through the day, but then turn cooler
for tonight.

.LONG TERM...(Monday through Saturday)
ISSUED AT 401 AM CST Sun Dec 4 2016

Forecast is an active one throughout the 7 days as winter is coming.
Precip should come to an end tonight...with Monday remaining
partly/mostly cloudy and southerly winds keeping the high temps near
40 or so.  However, much colder air is digging into the Plains for
the second half of the work week and into the weekend.

For Monday and Tuesday, the southerly winds and weak warm air
advection on Monday will give enough of a warm up to keep the
majority of the precip for Monday night and Tuesday liquid. Some
RA/SN mix possible mainly NW of the IL river valley. The better
chances for significant QPF are in the south. 00Z model runs have
slowed, resulting in a showery Tuesday.  The surge of colder Arctic
air makes its way into the region and by Wednesday, most areas north
of Interstate 70 have high temperatures below freezing...everywhere
on Thursday.

Cold Arctic air bottoms out the temps to wrap up the week as highs
on Friday not making it out of the 20s. Precip comes back into the
forecast for a snowy weekend with an open wave rippling through the
midsection of the country. Major timing differences between the GFS
and ECMWF still at this point, varying by about 6-18 hrs. The timing
differences have gotten worse with this round of model data.
In the blends, the pops are stretched over a longer period than will
likely shake out...once the models find some common ground.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1123 AM CST Sun Dec 4 2016

Large area of snow frequently producing LIFR conditions over most
of the TAF sites at midday, with visibilities down to about 1/2
mile at times. Areas near KDEC/KCMI have been in a rain/snow mix
with higher MVFR ceilings at times, but currently think these
will come down as well this afternoon. Precipitation will be east
of the TAF sites by 00Z, and the focus beyond that is the timing
of any clearing. Am leaning toward a more pessimistic solution at
this time which would linger IFR conditions most of the night.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM CST this evening for
ILZ027>031-037-038.

&&

$$

UPDATE...Geelhart
SHORT TERM...Auten
LONG TERM...HJS
AVIATION...Geelhart



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