Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 060956

Area Forecast Discussion
National Weather Service Lincoln IL
356 AM CST Tue Dec 6 2016

.SHORT TERM...(Today and tonight)
ISSUED AT 356 AM CST Tue Dec 6 2016

Precip is finally getting into the CWA early this morning, and
though mosaic radar returns showing precip as far northwest as I-55,
local radar returns showing that precip not getting that far. So,
radar returns combined with observations indicating that precip is
reaching mainly southeast IL at the moment. Based on blend of
models, highest pops should be in eastern and southeastern parts of
the CWA, just for this morning. Lower pops will extended northwest,
with all areas northwest of I-55 being dry this morning. With temps
being below freezing in northeast areas currently, the slight chance
of freezing rain is still warranted, so will be leaving it in the wx
grids. Fog has developed over most of the area north of I-70 with
some areas in the north seeing visibilities below 3 miles, and even
PIA at 1/4 mile. Fog will remain in the grids as well and since
cloud cover will continue through the day, fog will likely hang
around til around noon.The remainder of today through tonight will
be dry as the weather system quickly moves east and a high pressure
ridge builds into the area tonight from the west. Skies should
scatter out and then clear tonight as the ridge moves in. Cloud
cover today will allow temps to range from the mid 30s in the north
to the mid 40s in southeast IL. Clear skies and high pressure
building in will cause temps to drop well below freezing, reaching
the lower to mid 20s across the area.


.LONG TERM...(Wednesday through Monday)
ISSUED AT 356 AM CST Tue Dec 6 2016

Cold temperatures on the way through the end of the week.  Next
precip system for the weekend still with immense variation in the
models. Chances for snow this weekend and into the first portion of
the week kept rather low considering the inconsistent forecasts.

Cold Arctic air makes its way into the region and by Wednesday, most
areas north of Interstate 70 have high temperatures at or below
freezing...everywhere on Thursday. Overnight lows dropping each day
until widespread teens Thu night/Friday morning.  Winds Friday
morning will be up a bit, dropping wind chills to single digits.

Models still having issues with the weekend.  GFS and ECMWF are
lacking consistency and continuity with themselves, much less each
other.  The 500 mb flow across the CONUS after Friday becomes almost
zonal.  The GFS, ECMWF and Canadian global have a wave moving into
the Pac NW on Friday night.  The ECMWF and the Canadian both dampen
the wave considerably, maintaining the zonal flow. The GFS amplifies
more, and as a result deepens the surface low whereas the ECMWF and
Canadian treat it essentially like an open wave.  The deeper and
more progressive GFS starts the precip quicker on Sat night...and
ends it by Sunday night. The ECMWF and the Canadian are slower to
start and slower to end.  As a result...pops remain in the forecast
for the latter half of the weekend and into the first portion of the
work week.  The upside of the pattern shift for the weekend is that
southerly flow ahead of the storm system will warm the temps enough
so that the max temps by Sun are at least a touch over freezing.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1150 PM CST Mon Dec 5 2016

Plenty of forecast challenges with the 06z TAFS tonight. The
latest IR/Fog satellite loop continues to show the edge of the
LIFR ceilings and visibility near the PIA and BMI TAF sites. In
the past hour PIA has varied from 4SM to 1SM and BMI from 1/4SM to
2SM. Believe the average visibility will range from 1-2 miles
through 08-09z with broken LIFR ceilings being predominant. The
CONSShort blend seems to have finally caught on to the ceiling and
visibility trends, so there is fairly high confidence that LIFR
conditions will dominate at PIA and BMI through daybreak.

Primarily looking at the development of MVFR conditions across the
rest of central Illinois the next few hours with low level warm
advection and ceilings around 1 Kft upstream. Visibility is only
expected to bottom out around 2-3SM around 10-11z and then rebound
quickly by mid-morning.

After a shift in the wind to a northwest direction after daybreak we
should see the strong low level inversion get eaten away slowly
during the morning hours. This will allow for more mixing, which
should result in a dissipation of the fog and low ceilings by
late morning/early afternoon.




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