Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 141748

Area Forecast Discussion
National Weather Service Lincoln IL
1148 AM CST Thu Dec 14 2017

Issued at 1045 AM CST Thu Dec 14 2017

Forecast generally looked on track today and just a minor update
for sky cover. Much lighter winds today as weak 1022 mb high
pressure over nw IL drifts across central and southeast IL this
afternoon, and into the Ohio river valley by midnight tonight.
Stratocumulus clouds with ceiling of 2500-3500 ft is over areas
south of I-74 at late morning and these clouds will tend to linger
into the afternoon. Plus more of these low clouds over IA will
drift se into central IL during the afternoon. Also seeing some
cirrus clouds over area where mostly sunny skies from I-74 north.
So sky cover will be variable today with more low clouds over
southern and western CWA. 1030 am temps ranged from lower 20s from
Lacon and Bloomington ne to lower 30s south of I-70. Highs 30-35F
with mildest readings south of I-70. North to NW winds only 5-10
mph rest of today so not much of a wind chill.


.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 18Z TAFS through 18Z Friday afternoon)
Issued at 1150 AM CST Thu Dec 14 2017

Weak 1022 mb high pressure over nw IL will drift southeast over
the Ohio river valley by 06Z/midnight tonight. Then an upper level
short wave trof will slide se across central IL overnight and
exit se of the area by mid morning Friday. Moisture is lacking
with this system so no precipitation expected over central IL
airports. Broken MVFR clouds of 2.5-3k ft along I-74 will lift to
VFR during the afternoon of 3-4k ft and scatter out at times.
Expect scattered to broken stratocumulus clouds of 3-5k ft
this evening and become more broken overnight, and scatter out
again between 14-16Z Friday as subsidence and dry air arrive in
wake of short wave trof. North winds 4-8 kts early this afternoon
will veer WNW late this afternoon and weaken to 3-5 kts by sunset.
Expect WSW winds 5-10 kts overnight to become WNW and increase to
10-15 kts during mid morning Friday with gusts 15-20 kts by late
Fri morning.





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