Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 172052

Area Forecast Discussion
National Weather Service Lincoln IL
252 PM CST Tue Jan 17 2017

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 252 PM CST Tue Jan 17 2017

08z/2am surface analysis shows 1008mb low near Chicago, with cold
front extending southward along the I-57 corridor.  A few showers
are ongoing ahead of the front near the Indiana border: however,
most of the precipitation has come to an end across central
Illinois.  The widespread dense fog from last evening has also
mostly dissipated, except for locations along/north of a Canton to
Bloomington line where visibilities are 1 mile or less.  HRRR has
been consistently showing dense fog over eastern Iowa spilling E/SE
along the I-74 corridor this morning: however, based on prevailing
W/SW boundary layer flow, think its forecast takes the fog a bit too
far south.  Based on current upstream obs over northern Missouri,
have decided to trim the southern row of counties from the Dense Fog
Advisory to only include Knox, Stark, Marshall, Peoria, and
Woodford.  Still some question as to how quickly the fog will
dissipate later this morning, with the Rapid Refresh showing it
clearing the area as soon as 15z, while the HRRR lingers it until
closer to 18z.  Given lack of strong dry advection in the wake of
the departing low, have opted to go more pessimistic and have
therefore lingered areas of fog across the north through midday.
Once the fog dissipates, overcast conditions will prevail for the
balance of the day and through tonight as well.  Highs today will
range from the upper 30s around the lower 50s near
the Indiana border.  Lows tonight will generally be in the lower to
middle 30s.


.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 252 PM CST Tue Jan 17 2017

High pressure moving off to the east will allow moisture to return
to the area just ahead of the next weather system coming out of the
southern plains. This moisture will interact with a
developing/deepening system to bring precipitation to the CWA
beginning Thursday and continuing into Thur night. Models have
shifted the track of this system little further northwest of
previous forecast, moving it across southern and southeast IL. With
the further northwest track and the warmer temps, all precip should
be in the form of rain through the period. Based on this track, also
seeing an increase in MUCAPE in southern IL, so have included schc
of thunder in southeast and eastern IL Thur afternoon through
Thursday night. As the surface trough and 500mb trough move through,
precip chances will continue Friday morning, but then should become
dry for the afternoon as things push off to the east and northeast.

Upper level flow will then become more southwest with an upper level
low pressure area to the west and northwest. This setup will
continue to bring warm air into the region and an isolated threat of
diurnal type precip...for into the weekend. For now, will just keep
small chances in the grids to account for this. The next main threat
of precip will begin Sunday and then increase through Sunday night
and Monday. Models show significant differences as to timing,
location, and intensity of the system so pops are in for more
periods than probably will occur. However, best chances look to be
Sun night and Mon.

Temps will warm rest of the week and into the weekend, with mildest
temps being Saturday when some spots could reach the lower 60s.
After the system on Sunday, temps will cool down a bit, but still
remain above normal for this time of year.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1124 AM CST Tue Jan 17 2017

Main issue much of the forecast period will be persistence of
IFR/LIFR type ceilings. Large area of 500 foot ceilings covers
much of central Illinois at midday, although some MVFR conditions
not too far south of the KSPI-KCMI corridor. Forecast soundings
showing some potential for ceilings here to lift just above 1,000
feet at times later this afternoon, but with the uncertainty, will
keep the ceilings on the lower end for now. Visibilities have
lifted in most places after the earlier fog, but some potential
for it dropping back down into the 1-3 mile range late tonight.
Some more wholesale improvement in ceilings is possible late in
the period.




SHORT TERM...Geelhart
AVIATION...Geelhart is the U.S. government's official web portal to all federal, state and local government web resources and services.