Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180527
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1127 PM CST Sun Feb 17 2019

.UPDATE...
Issued at 904 PM CST Sun Feb 17 2019

The upper level trough associated with today`s storm system
lingers over the upper Midwest, with an embedded shortwave impulse
headed through the area, bringing more precipitation to the
western I-72 corridor and southeastward toward the I-70 corridor.
Moisture depth increasing and upper level temperatures decreasing
has allowed widespread freezing drizzle earlier in the evening to
start transitioning back to snow due to a microphysical
environment more favorable for ice crystal growth. Had previously
extended the winter weather advisory for areas north of I-70 to
midnight, mainly due to the significance of the freezing drizzle,
but also due to continued potential for light snow accumulations.
After midnight, freezing drizzle should be ended across the area,
and snow will be tapering off from south to north. Updates have
focused on trends to increase precipitation chances and add
accumulations this evening, and to incorporate trends in
precipitation type.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 245 PM CST Sun Feb 17 2019
Cloudy and light winds as the low passes through the Midwest.
Winds in the western portions of the state coming around to more
westerly, a little more light and variable elsewhere as the low
passes. Stronger radar returns to the north associated with the snow
and some wintry mix along an inverted trof axis that will
continue to play a role in the weather through this evening.
Although there are fewer returns over Central IL, reports of
freezing drizzle are common, with slick roads and reduced
visibilities. Had extended the WSW in the south due to reports
from affected counties...and will likely let the advisory run its
course, particularly as the temps drops at the end of day.

For tonight, maintaining the clouds and wintry mix of snow,
drizzle/fz dz into the early evening in some locations. Overnight
lows will drop into the 20s by morning. Winds slowly coming around
to more northerly as the low passes will help to keep tomorrows
highs down in the 30s as the precip takes a brief break.

.LONG TERM...(Monday night through Sunday)
ISSUED AT 245 PM CST Sun Feb 17 2019
As the current system shifts out to the east, another wave digs
into the trough over the western half of the country. This
eventually becomes more southwesterly aloft, but easterly flow at
the surface keeps the temperatures rather cool. This stability is
uprooted by the next system that eventually develops as the
western trough kicks out into the Plains. Precipitation starting
Tuesday night as snow in the blended model runs. However, there is
a quick transition to freezing rain in the grids as the
probability of ice drops off. Potentially more impactful than that
is a modeled deep isothermal layer near the freezing mark over the
CWA. The ice accumulations possible before dawn on Wednesday is
the major concern of this forecast. It is worth mentioning that
the amount of snow on the front end and the transition back to
liquid by midday on Wednesday work against accumulations of ice.
Both the GFS and the NAM are modeling this isothermal layer.

Beyond midweek, another wave digs into the western trough and sets
up for another round of precip for the weekend. Daytime highs at
this point look warm enough to result in rain, with wintry precip
possible in the overnight hours.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1127 PM CST Sun Feb 17 2019

Primarily MVFR cigs across central IL presently, with IFR along
and north of I-74 coincident with a region of light snow and some
MVFR vsbys settling southward. Best chances for precipitation will
be along I-74 sites KPIA-KBMI-KCMI, although KSPI and KDEC could
also see some light snow, or patchy freezing drizzle overnight.
Precipitation should diminish by around 12Z, although MVFR cigs
should last until after 01Z. Winds NW 5-12 kts, gradually turning
northward and decreasing.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight CST tonight for
ILZ027>031-036>038-040>057-061.

&&

$$

UPDATE...37
SHORT TERM...HJS
LONG TERM...HJS
AVIATION...37


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