Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 172009

Area Forecast Discussion
National Weather Service Lincoln IL
309 PM CDT Tue Oct 17 2017

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 300 PM CDT Tue Oct 17 2017

Brisk southwest winds this afternoon will diminish this evening as
decoupling occurs with sunset. An steady pressure gradient will
keep overnight winds from becoming calm, as winds become southerly
at 5 to 10 mph with time.

High pressure anchored to the southeast of Illinois will keep
skies mostly clear through tomorrow, with the exception of a few
cirrus clouds at times. A weak upper level disturbance in the 500
mb flow will keep slightly lower thickness over Illinois tomorrow.
However, we still could see high temperatures climb a degree or
two warmer than today. Southerly winds at 10-20 mph will add some
cooling effect to the day, especially in the shade.


.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 300 PM CDT Tue Oct 17 2017

The longwave ridge in the Plains will begin to translate eastward
Wed night and Thursday, bringing rising heights and steady warm
air advection. Coupled with high surface pressure, dry and
gradually warming conditions are forecast through Friday night.
The next chance of rainfall is still projected over the weekend.
However, there are some differences in the extended models about
the timing of the cold front into central Illinois. The GFS and
Canadian GEM bring the front across IL Saturday night, while the
ECMWF delays the FROPA about 6 hours. The onset of persistent
rains will likely be affected by a later FROPA, but all 3 models
show pre-frontal showers developing on Saturday across our
forecast area. So we did not alter the timing from consensus.

Due to decent agreement with Sat night being the primary precip
period, we left some categorical PoPs /80+%/ in our western
counties after midnight Sat night. Otherwise, Likely /60-70%/ PoPs
were advanced across our forecast area Sat night and Sunday
morning. Thunder potential is not high, with MLCAPE values of
250-300 J/kg, but we kept a mention of thunder due to the
combination of marginal shear parameters with the instability.

High temps on Friday and Saturday should be the warmest of the
next week. Any areas that see significant sunshine on Saturday
will climb a few degrees warmer than Friday, into the upper 70s
to near 80.

Showers will make an exit on Sunday as the cold front departs to
the east. Cooler conditions will develop on Sun and Mon, as highs
drop about 10 deg from Saturday. A reinforcing push of cold air
will arrive on Tuesday, limiting highs to the upper 50s to low
60s. Spotty showers or sprinkles could develop Monday and Tuesday
under the cold pool, especially with the upper trough axis and
waves of energy extending into Illinois during that time.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1252 PM CDT Tue Oct 17 2017

Winds are the main concern for aviation for the 18z TAF period. A
tightening pressure gradient across Illinois is producing
southwest wind gusts of 24-26kt this afternoon. The stabilizing
effects of sunset will cause gusts to diminish by early evening,
and wind speeds will drop below 10kt as the wind direction becomes

Winds will increase from the south by mid-morning tomorrow, with
some gustiness expected again.

No significant clouds will develop over the next 24 hours.




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