Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 190545

Area Forecast Discussion
National Weather Service Lincoln IL
1145 PM CST Thu Jan 18 2018

Issued at 910 PM CST Thu Jan 18 2018

Diurnal temp falls tonight are being held on the slow side again
by steady southwest winds of 10-20 mph. Cirrus clouds are flowing
over the ridge in the Plains into northern and central Illinois.
Any thickening of that cloud cover could aid in keeping low temps
slightly warmer than under clear skies. However, the winds will be
the primary reason for milder low temps. Our east-southeast
counties temps dropped off more significantly already tonight due
to snow cover, with 9 pm temps down into the low 20s near
Lawrenceville, and Galesburg 31, Jacksonville 35. Dewpoints remain
on the dry side, so there is some room for temps to drop off.
However, have trended warmer with lows for areas west of I-57 and
maintained cooler readings east of I-57.

Tomorrow is looking mild, with many more areas seeing 40s for
highs, especially west of I-57.

Updates this evening were to the temps/dewpoints along with
slight increase to cloud cover in the NW half our forecast area.


.SHORT TERM...(This evening through Friday)
ISSUED AT 301 PM CST Thu Jan 18 2018

Southwest winds will continue across the area tonight and tomorrow
as high pressure sits across the southeastern US and a mid level
ridge begins to build across the eastern half of the US. This will
bring much warmer air into the area and should see temps above
freezing tomorrow across the whole CWA. Skies will also be mostly

Temps will fall below freezing overnight again, but near to the
level they have been the past week or so. Again, much warmer
tomorrow with many areas getting into the 40s.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 301 PM CST Thu Jan 18 2018

Ridge will continue to build across the area with continued
southwest flow on the sfc. This warmer air will melt a lot of the
snow into Friday night and as an inversion begins to setup, some
fog will be possible late Friday night and early Sat morning. So
have added patchy fog for this period. The waa will continue
through the weekend ahead of the next weather system that will
begin to bring some light WAA precip to the area Sat night into
Sunday. With the light precip and continued inversion, more fog
will be possible Sat night into Sunday. So will up the coverage of
fog to areas for Sat night and Sun. By Sunday night, once precip
chances increase to likely or higher, the fog will dissipate out.
The front should be moving through the late Sunday night through
Monday morning with only chance of lingering precip Monday
afternoon. Models show a decent clear area coming into the CWA Mon
afternoon along with a little bit of colder air. So precip could
become mixed with snow in some areas to the west during the
afternoon and Monday evening. Beyond this system weather should
return to dry, though the older ECMWF showed some kind of weak
wave moving through the area Wed and Wed night. However, GFS and
newer ECMWF show dry weather through the middle of the week.

Temps will begin very warm ahead of the weekend weather system but
then moderate lower after the system. Still looks as though
daytime highs will be above freezing, with some areas getting into
the 40s for Mon through Thur.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1145 PM CST Thu Jan 18 2018

Main concern for that TAFs will be the LLWS conditions tonight
into Friday morning and again Friday evening/overnight. A
strong southwesterly LLJ will continue the rest of the night
across central IL looks to peak at 45-50KT around 2K feet, with
40KT winds as low as 1K feet. The LLJ is projected to weaken after
14z, as turbulent mixing increases after sunrise. Sustained winds
the rest of the night look to remain in the 10-14kt range out of
the SW, then increase with some gusts to 20-25kt tomorrow.

An even stronger LLJ is projected to develop Friday evening, with
50-55KT southwest LLJ max across central IL.

The only clouds of note will be a wave of cirrus streaming over
the upper level ridge in the Plains. No significant clouds nor
visibility issues are expected through 00z tomorrow evening.




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