FXUS63 KILX 180915

Area Forecast Discussion
National Weather Service Lincoln IL
315 AM CST Mon Dec 18 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 315 AM CST Mon Dec 18 2017

08z/2am surface analysis shows overcast conditions across central
Illinois. The lowest ceilings and drizzle have been primarily
confined to locations west of the Illinois River and along/east of
the I-57 corridor. Based on satellite/radar trends as well as
latest HRRR ceiling/visby forecast, think patchy drizzle and fog
will persist through mid-morning before dissipating and shifting
further east into Indiana. The main short-term forecast challenge
will then focus on how quickly skies will clear later today into
tonight. Current IR satellite imagery shows the back edge of the
low clouds well to the west from central Iowa to eastern Kansas.
Both NAM and RAP forecast soundings suggest partial clearing could
occur west of the Illinois River as early as midday...with
clearing progressing slowly eastward to near I-57 by late
afternoon. Models tend to clear skies too quickly this time of
year: however, given the 10-15mph W/SW winds expected to prevail
throughout the day, think they seem quite reasonable. As a result,
will start the day overcast across the board...with partly to
mostly sunny skies developing west of I-57 this afternoon. Further
east toward the Indiana border, skies will remain mostly cloudy
until early this evening. High temperatures will be in the upper
40s and lower 50s. Low temperatures tonight will drop into the
upper 30s under mostly clear skies.


.LONG TERM...(Tuesday through Sunday)
ISSUED AT 315 AM CST Mon Dec 18 2017

Warmest day of the forecast period still appears to be Tuesday, as
ample sunshine and mild W/SW winds ahead of an approaching cold
front push high temperatures well into the 50s. Once the front
passes, a slightly cooler airmass will spill into the region,
allowing temps to drop into the 40s on Wednesday. The cooler
weather will be short-lived however, as winds shift back to the
S/SW and temperatures once again climb into the 50s for Thursday
and Friday.

A significant storm system is still slated to arrive by the end of
the week, but its onset has been delayed by about 6-12 hours. 00z
Dec 18 GFS and ECMWF are in fairly good agreement with a cold
front pushing through Illinois during the day Friday, while the
GEM holds the front to the west until Friday evening. Given
slowing trend, think Thursday/Thursday night will remain
dry...with rain chances developing across the area on Friday. Will
need to keep an eye on how quickly the front departs late Friday,
as any lingering rain showers will change to a few snow showers
behind the departing front Friday night. Little or no snow accumulation
is anticipated.

After that, a trend toward much colder weather is evident over the
upcoming weekend into next week. An area of weak lift could
potentially bring a period of light snow to portions of central
Illinois on Sunday: however, confidence in a mesoscale feature on
the models that far out is quite low. At this point, the main
take-away for the weekend will be the colder weather...with high
temps falling into the 30s by Sunday...and even further early
next week.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1122 PM CST Sun Dec 17 2017

Narrow corridor of MVFR and even VFR ceilings in central Illinois
is being squeezed from both sides, and IFR ceilings below 1,000
feet will quickly become the norm at all TAF sites. Some patchy
drizzle and fog should accompany the lowest ceilings, but a major
fog event is not expected. Some slow improvement in ceilings is
expected Monday morning, but it will likely be toward early
afternoon that ceilings break out above the 3,000 foot range.




LONG TERM...Barnes
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