Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 240227

Area Forecast Discussion
National Weather Service Lincoln IL
927 PM CDT Fri Mar 23 2018

Issued at 925 PM CDT Fri Mar 23 2018

Initial wave of rain is progressing from SW to NE as expected, as
increasing isentropic lift advances across IL. However, rapid
evaporative cooling on the leading edge has produced a period of
sleet in our NW counties, despite surface temperatures in the mid
to upper 40s. Radar bright band indicates this narrow channel of
sleet, which should continue to shift to the N-NE the rest of the
night. A warm surge aloft later tonight is still indicated in the
high res models, which will push the rain-snow line to our far
northern CWA between 4-7am. The surface low track is still
forecast to track from W Missouri across S IL. That track still
supports a persistent NW to SE band of snowfall across our far
northern counties, aided by dry NE flow to keep wetbulb temps
just below freezing through the precipitating layer in our
warning area and northern advisory area. The strong winds have
already developed, and any snowfall later tonight will get blown
as it falls, creating reduced visibilities. The wet snow should
not drift all that much, but the intensity of snowfall should
quickly overcome the grounds ability to melt the snow, with a
couple inches of snow my sunrise in our far N CWA. Overall, do not
see a need for any changes to the going winter headlines, and
amounts appear on track to this point. Once the rain-snow line
develops, we will get a better handle on how the atmosphere is
responding to the precip development. That will provide some
insight toward any possible snowfall adjustments with the
overnight update.


.SHORT TERM...(This evening through Saturday)
ISSUED AT 237 PM CDT Fri Mar 23 2018

Low pressure center at surface starting to move now and seen in
surface data over western KS. Resultant winter storm is the main
focus for the period through Saturday as the surface low moves
over MO and over extreme IL. Overrunning rain to develop and move
into the region this evening. With cooling due to dry air in place
currently, pcpn will change over to snow over the northern
portions of CWA tonight.

Lift remains significant through the day on Saturday, with
temperatures around freezing over the northern CWA. This will
allow accumulation of significant snow over the north, with 6 inch
plus amounts in the far north sections. Northeast third of Mclean
and northern quarter of Vermilion may approach 6 inch amounts by
the time snow ends, so will have to watch those areas, as kept
advisory in place.

Winds will also increase overnight and remain easterly at mainly
20 gusting to 30 to 35 through day as the low center moves south
of region. Even in the southern sections, afternoon temperatures
in the upper 30s and with the winds it will be a cool and rainy
day. Rainfall amounts through Saturday over southern sections in 1
to 1.5 inch amounts.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 237 PM CDT Fri Mar 23 2018

Upper flow remains southwesterly after this current short wave
moves through. With that, a second wave develops late Sunday and
pushes moisture and associated showers in the southwest flow into
the area Monday, which will continue into early Wed over the
southeast sections, when the front finally moves through. Rainfall
totals with this extended period of showers will range from 1.5 in
the northwest to around 2 in the southeast.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 700 PM CDT Fri Mar 23 2018

VFR conditions will start out the 00z TAF period, but MVFR
conditions will develop overnight as low pressure approaches from
the west, and rain overspreads central IL from SW to NE. As the
air above the ground cools due to evaporative cooling, the rain
will mix with or change to snow and sleet across the northern
terminals along I-74. The change to mixed precip will cause
ceilings and visibilities to lower to IFR by tomorrow morning,
with IFR conditions for much of the day on Saturday, especially
for PIA, BMI and possibly CMI.

The surface low will track from northern KS tonight across
central MO Saturday morning, and eventually across far southern IL
on Saturday.

Precip type will be driven initially by cooling aloft, then a warm
surge above the ground will change snow/sleet back to rain for the
I-74 corridor TAF sites, mainly between 09z/4am and 13z/8am.
Cooling will shift southward Sat afternoon, as the surface low
pulls to the southeast of central Illinois. Ceilings will drop to
IFR as precip becomes mixed or all snow, with visibility IFR as
well. IFR conditions look to continue Sat afternoon through the
end of this TAF period.

East winds will start out 10 to 20kts this evening, with speeds
and gusts increasing through the night as the pressure gradient
tightens with the approach of the low pressure center.
gusts will increase to 25-35 kts at times tomorrow.


Winter Weather Advisory until 7 PM CDT Saturday for ILZ027-029-

Winter Storm Warning until 7 PM CDT Saturday for ILZ028-030-031.



SHORT TERM...Goetsch
LONG TERM...Goetsch
AVIATION...Shimon is the U.S. government's official web portal to all federal, state and local government web resources and services.