Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 141137

Area Forecast Discussion
National Weather Service Lincoln IL
537 AM CST Thu Dec 14 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 328 AM CST Thu Dec 14 2017
Storm system exiting the region to the west this
colder air filters into the region in the northwesterly flow
aloft. Partly cloudy skies likely to continue today as the
pressure gradient relaxes and winds decrease considerably from
yesterdays blustery conditions. Colder air in place will keep high
temperatures mainly below freezing for much of Central IL. Light
northerly winds will contribute to another cold night as well,
with pressure building back into the Midwest, at least briefly.
Weather pattern gets more complicated moving into the weekend and
beyond as a series of waves diving into the western US shifts the
pattern aloft. Models lack continuity, particularly at the end of
the weekend as the first of the waves brings a chance of precip to
the region.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 328 AM CST Thu Dec 14 2017

Weak warm air advection kicks in for Friday with a west wind
trying to pull some of the warmer air into the region, and highs
start to move into the mid to upper 30s as another wave dives into
the western trough, altering the flow pattern aloft. The
remainder of the forecast centers around the interaction between
the energy moving onto the Pac NW coast on Friday, and an upper
low over the Baja. Either way, the westerly flow aloft allows for
a slight warm up and weak ridging over the eastern half of the
country as the wave digs in. The issue had previously been an
either or situation as to whether or not the waves would phase.
However, most recent models not only keep them separate, but bring
the wave onshore, digs it in to the SW CONUS while splitting
itself into two discernible waves, kicking the Baja low out over
the southern half of the CONUS. The precip previously anticipated
for Sunday is currently tracking further south, over the southern
tier of the country, reducing pops to chance. The other split wave
anchors the western trough deep in the SW, effectively keeping the
flow more westerly/increasingly southwesterly through the first of
next week. ECMWF is more distinct with sheering out the wave over
the CONUS, lingering some chances for precip, or at the very least
cloud cover, through Monday morning. Temperatures remain more
moderate in the extended, but rely heavily on the behavior of the
waves to the southwest. As of yet, models have not had nearly
enough consistency for significant confidence.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 533 AM CST Thu Dec 14 2017

Surface low moving out to the east this morning and high pressure
building into the region. Lighter winds anticipated as pressure
gradient decreases. Lingering clouds on the MVFR/VFR cusp this
morning in Central IL, but clearing trends on sat imagery. Have
left the cigs out of BMI altogether, and improving other sites
later this morning. Mid level clouds and light winds anticipated
today and through the overnight. Some variability likely in the
wind fields tonight under the ridge. Beyond this morning, VFR




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