Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 150544

Area Forecast Discussion
National Weather Service Lincoln IL
1144 PM CST Thu Dec 14 2017

Issued at 915 PM CST Thu Dec 14 2017

Plenty of energy in the northwest flow aloft to support light
snow/flurries development with the surface trough that will push
across the area later tonight into Friday morning. Precip
potential should wane by late morning tomorrow, as the bulk of the
upper level energy with this shortwave shifts east of Illinois.
Clouds should dominate the skies overnight, with only a brief
period of cirrus overcast for our northeast counties for the next
couple of hours. The cloud cover will help to slow down the
diurnal temperature falls. Lacon earlier dipped to 16F, which will
likely be there low for the night, since clouds have overspread
that area and their temp rose to 19F. Have tried to adjust the
hourly temps to reflect expected trends as cloud cover advances.

Updated to expand the coverage of flurries in the NW half of our
forecast area after midnight through 15z/9am Friday, based on
expected lift and depth of low level moisture with the surface
trough. The trough looks to lose support from aloft later in the
morning, so little to no precip is expected in east-central and
southeastern IL as we head into Friday afternoon.

Updated forecast info will be available shortly.


.SHORT TERM...(This evening through Friday)
ISSUED AT 300 PM CST Thu Dec 14 2017

Partly to mostly cloudy skies prevailed across central and
southeast IL today with stratocumulus clouds 3-4k ft more
prevalent along and south of I-72. Weak 1020 mb high pressure was
settling into central IL this afternoon and providing light to
calm winds. Temps at mid afternoon ranged from the upper 20s north
of Peoria, to 34F at Lawrenceville. A short wave trof moving se
into central WI/IA/NE will pivot se across central IL overnight
and exit into the ohio river valley during Friday morning. Limited
moisture with this system so just mostly cloudy skies tonight and
a chance of flurries northern cwa overnight into early Fri
morning. Lows overnight in the lower 20s with light winds this
evening becoming WSW 5-10 mph during overnight.

Subsidence behind short wave trof moving into the TN river valley
during Friday afternoon to allow skies to become partly sunny over
CWA. WSW winds 10-15 mph and gusts up to 20 mph on Friday with
highs in the mid 30s from I-74 ne and near 40F far SW CWA and
southeast IL.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 300 PM CST Thu Dec 14 2017

A quiet/dry stretch of weather expected Friday night through Sat
night across central/se IL as high pressure drifts east from the
southern plains and across the southeast states. SW winds and
ample sunshine Saturday to warm temps into the upper 40s and lower
50s which is 10-15F above normal for mid December.

A weather system developing over the southern plains sat night
will eject ne into the mid MS river valley during Sunday. This
will likely spread rain showers ne across the CWA during Sunday
morning and could start as a mix early Sunday morning over
northern CWA. But little or no snow accumulations expected as much
of this precipitation falls as rain. Lows Sat night in the low to
mid 30s. Highs Sunday in the low to mid 40s. A much weaker system
ejecting ne over area overnight sunday night into Monday morning
may bring isolated light rain/snow showers. Highs Monday range
from mid 40s northern cWA to lower 50s in southeast IL.

Another stretch of quiet/dry wx expected from Tue through Thu
morning as high pressure settles into the mid MS river valley on
Wed. Above normal temps continue with highs in the mid 40s to
around 50F Wed/Thu while lows in the upper 20s and lower 30s.
Models show another stronger low pressure system ejecting ne into
the Midwest later Thu and Thu night bringing next chance of
precipitation with much colder air following this system late next


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1144 PM CST Thu Dec 14 2017

A weak shortwave in the 500mb flow and sfc trough are triggering
some MVFR strato-cumulus and a few flurries across Iowa, SE MN,
and SW WI. The band of clouds/flurries is slowly progressing into
our northwest counties, and will likely affect our TAF sites
the rest of tonight. Did not include VCSH at this point, due to
very minor flurry activity expected.

Timing of MVFR conditions looks to be most of the night and
possibly through mid-morning. Some improvement to low VFR is
expected later tomorrow morning, per HRRR ceiling projections.
During the day tomorrow, there looks to be enough residual mid-
level moisture for VFR clouds to linger through the day, but
nothing significant to aviation. Precip/flurry chances appear to
diminish by afternoon, as the surface trough shifts into Indiana.

Winds will be light west-southwest or variable the rest of tonight,
with increasing west winds to 10G22kt by tomorrow afternoon.




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