Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 150947

Area Forecast Discussion
National Weather Service Lincoln IL
347 AM CST Fri Dec 15 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 327 AM CST Fri Dec 15 2017
Cloudy day is anticipated today for Central Illinois, as a
north/south orientation of upper level flow just to the west puts
the region in the axis of an upper trof. Cyclonic flow will
continue through the day and keep the clouds in place for the most
part. Southwesterly winds at the surface will help with some warm
air advection and bring the temps up into the mid-upper 30s/near
40. Should the southwest clear some of its clouds later in the
day, sunshine could bring up max temps in the southwest and create
an even steeper temp gradient from SW to NE. Those same clouds
anchored over the area tonight will keep the temps from plummeting
too far...with minimums in the upper 20s.


.LONG TERM...(Saturday through Thursday)
ISSUED AT 327 AM CST Fri Dec 15 2017

The remainder of the forecast is centered on the wave currently
moving onto the Pacific coast this morning. This same wave digs
into the western coast of the CONUS, and kicks the upper low
currently in the Gulf of California out and across the southern
tier of the country. That same wave results in a storm system that
pushes rain/precip north of the Ohio River Valley and into Central
IL for Sunday. PoPs have gone back and forth with each run of the
models as there is a lack of continuity as to the track of the
surface system. The wave that replaces it over the desert SW has
alternately split, phased, or become cutoff from the rest of the
country with each run. Models are starting to show some repetition
with shearing out some of the energy and bringing it through the
Midwest as a weak frontal boundary on Monday night with some
precipitation. Just as quickly, the 00Z ECMWF came in with a
slower progression of a more compact wave and passing it to the
south of the area. For now, best chances for precipitation is the
rain on Sunday, should the system take a slightly more northerly
track. Temperatures throughout the extended remain impacted by
the deep trough over the SW keeping the orientation
southwesterly...and slightly above normal highs for the latter
half of December.


.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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