Area Forecast Discussion
Issued by NWS Central Illinois

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535
FXUS63 KILX 182009
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
309 PM CDT Fri Aug 18 2017

.SHORT TERM...(This evening through Saturday)
ISSUED AT 309 PM CDT Fri Aug 18 2017

Vigorous short-wave trough noted on 19z/2pm water vapor imagery
over western Wisconsin will track eastward into the Great Lakes
tonight. Synoptic lift associated with this feature will help
trigger scattered convection across Iowa over the next couple of
hours...with this activity pushing into central Illinois this
evening. Current satellite imagery is beginning to show a few
cells developing just south of a weak surface low near Des Moines,
Iowa. These storms will become more widespread later this
afternoon as they track E/SE and spill into the Illinois River
Valley early this evening. HRRR has been quite consistent
today...showing a few storms arriving across the far NW KILX CWA
around Galesburg by 00z/7pm. With daytime instability gradually
waning after dark and strongest upper dynamics remaining further
north in conjunction with the short-wave, think areal coverage of
convection across central Illinois will remain limited. As a
result, have opted to go with scattered wording in the forecast
for tonight. Most of the activity will push eastward into Indiana
and diminish toward dawn. With partial clearing expected late
tonight and plenty of boundary layer moisture in place from
rainfall during the evening, think patchy fog will develop.
Overnight lows will drop into the lower to middle 60s. A mostly
sunny and dry day is anticipated on Saturday, with afternoon highs
topping out in the lower to middle 80s.

&&

.LONG TERM...(Saturday night through Friday)
ISSUED AT 309 PM CDT Fri Aug 18 2017

Once the short-wave tracks toward the East Coast, a zonal flow
pattern will develop across the CONUS early next week. Rising
upper heights will allow temperatures to climb into the upper 80s
and lower 90s by Sunday and Monday, with heat index readings
reaching the middle to upper 90s Monday afternoon. While the bulk
of any significant convection will remain focused further west
across the Plains, a few models are suggesting scattered storms
could potentially reach west-central Illinois by Monday afternoon.
The GEM is particularly bullish with its eastward push of precip,
while the ECMWF is keeping all the convection well to the W/NW.
Since the flow remains flat through the period and the next major
short-wave is still off to the northwest, prefer the ECMWF
solution here. As a result, will confine PoPs to the far W/NW CWA
on Monday and keep them in the slight to low chance category.

All models agree that a vigorous wave will drop southeastward out
of Canada and dig a significant upper trough over the Great Lakes
by the middle and end of next week. With the corresponding cold
front progged to pass through central Illinois on Tuesday, will
continue to focus likely PoPs at that time. Once the front passes,
cooler and drier weather will arrive late in the period...with
highs dropping into the middle to upper 70s by next Thursday and
Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1249 PM CDT Fri Aug 18 2017

An upper-level disturbance will trigger scattered showers/thunder
across central Illinois tonight. While exact timing and areal
coverage of convection still remains in question, several high-res
models have been fairly consistent in bringing a few storms into
KPIA by around 01z. As a result, have continued the previous
forecast thinking...with TEMPO thunder after 01z at KPIA then
after 04z further east at KCMI. The scattered storms will push
east of the terminals late tonight and skies will partially clear,
potentially setting the stage for patchy fog. The HRRR does not
indicate significantly lowered visbys: however, the MET guidance
suggests at least some fog development. Given ample boundary layer
moisture enhanced by rainfall this evening and light/variable
winds, have decided to include 3-4 mile visbys after 09z at all
sites.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Barnes



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