Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200444

Area Forecast Discussion
National Weather Service Lincoln IL
1144 PM CDT Tue Sep 19 2017

Issued at 931 PM CDT Tue Sep 19 2017

Quiet weather is expected across central and southeast Illinois
overnight, with the possible exception of fog development.
However, recent high-resolution guidance has backed off on the
fog threat. While winds will begin to pick up over western
portions of the forecast area overnight as the pressure gradient
increases, they should stay quite light in the east. These light
winds, mostly clear skies, and low surface temperature/dew point
spreads support leaving fog mention in place in the east. Going
forecast was in good shape with only minor hourly tweaks needed.


.SHORT TERM...(This evening through Wednesday)
ISSUED AT 315 PM CDT Tue Sep 19 2017

Afternoon cumulus cloud cover will rapidly dissipate this evening as
an upper level ridge moves over the area. A pressure trough over the
Plains will start to initiate light southeast winds over the western
half of the state overnight limiting fog potential, however given
dewpoints in the mid and upper 60s, light winds, and the upper level
ridge, should be able to form fog over the eastern half of the
state. For Wednesday...models generally hold off any precipitation
with an approaching cold front until late afternoon so held off any
mention of thunder until then for areas N/W of Peoria. Strong
warming in SW flow should result in highs reaching around 90 degrees
to around 93 degrees for Springfield and Jacksonville. Tonight, lows
should remain mild, in the mid 60s.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 315 PM CDT Tue Sep 19 2017

The pattern of a longwave trough over the western U.S. and Ridge
over the eastern U.S. will amplify late this week and through the
weekend, resulting in a prolonged period of much above normal
temperatures. Initially, however a weakening cold front dragging
through the Mid Mississippi Valley will bring at least a slight
chance of thunderstorms Wednesday and Wednesday night as far east as
I-55. Subsequently...the southwesterly flow between the western
trough and eastern ridge will bring 17-20C 850 mb temperatures
Thursday through Monday. Highs mainly in the lower 90s will be
likely through Saturday, but have kept upper 80s Sunday and Monday
due to long range forecast uncertainty. The eastern ridge looks to
break down by the early to middle of next week as the western trough
progresses through the Plains and into the Midwest, likely
diminishing the late summer heat wave. A cold front associated with
this pattern change may also bring some thunderstorms back to
central IL and have included chance PoPs I-55 westward Tuesday.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1141 PM CDT Tue Sep 19 2017

Predominantly VFR aviation weather conditions expected across the
central Illinois terminals through the 06Z TAF valid time. Patchy
fog remains possible later tonight, but coverage is likely to be
too small to mention at this time. Also, a spotty shower or storm
may impact KPIA Wednesday evening, but again, expected coverage is
too low to mention.




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