Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180839

Area Forecast Discussion
National Weather Service Lincoln IL
339 AM CDT Fri May 18 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 339 AM CDT Fri May 18 2018

Weak upper low evident on 08z/3am water vapor imagery over
southern Missouri will be the main weather-maker across central
Illinois today. HRRR has been consistently showing showers
developing near the Illinois/Indiana border over the next hour or
two, then spreading further westward early this morning: however,
latest radar mosaic is largely devoid of precip immediately
upstream across Indiana. Radar trends are showing showers becoming
more numerous further south across southern Illinois into
southeastern Missouri in closer proximity to the upper low and
where the airmass is considerably more moist. Latest surface
analysis reveals a pronounced moisture gradient across the KILX
CWA...with dewpoints in the lower to middle 60s south of a Paris
to Shelbyville line...but only in the upper 40s and lower 50s
across the remainder of the area. This explains why precip has not
yet materialized across Indiana/eastern Illinois as the HRRR
suggests. Given the continued dry E/NE flow, think showers will
have a hard time developing northward...with locations along/north
of a Rushville to Bloomington line staying dry until mid to late
afternoon. Have adjusted PoPs to carry low chance south of I-72
this morning, with rain chances gradually spreading across the
entire CWA this afternoon. High temperatures will be held down due
to the clouds and showers, with afternoon readings remaining in
the lower to middle 70s. Scattered showers will continue into
tonight as the low meanders slowly northeastward. Greatest areal
coverage will likely be in the evening, followed by a decrease
overnight. Total rainfall with this system will be light,
generally less than one quarter of an inch.


.LONG TERM...(Saturday through Thursday)
ISSUED AT 339 AM CDT Fri May 18 2018

A few showers will linger across east-central Illinois into
Saturday morning before the low finally pushes into Indiana.
Thanks to partial clearing by afternoon, high temperatures will
rebound into the lower 80s. The next system of interest will then
come into the picture by the end of the weekend, potentially
brining a few strong to severe thunderstorms to the area Sunday
afternoon/evening. Low pressure will develop in the Texas/Oklahoma
panhandle Friday evening...then will track to near Kansas City by
Saturday evening. As it does, it will interact with a highly
unstable and moderately sheared environment to produce a round of
severe weather Saturday evening from Kansas City to Des Moines.
Some of this activity may track into the NW KILX CWA in a
weakening state late Saturday night. Have therefore included
chance PoPs along/west of the Illinois River at that time. As the
low slowly shifts eastward, the emphasis for storm re-development
will shift eastward into Illinois on Sunday. There is still some
disagreement among the models, particularly with the exact
positioning of the warm front extending eastward from the low. The
GFS is keeping the front further south across south-central
Illinois, while the NAM is pushing it further north. In either
case, a boundary will be in place across the region Sunday
afternoon, with both the NAM and GFS indicating ample instability
and sufficient low-level wind shear to produce scattered
thunderstorms. Have therefore carried chance PoPs across the board
Saturday afternoon and evening.

The low will lift into the southern Great Lakes and the trailing
cold front will gradually dissipate across the region early next
week. Additional showers/storms may develop ahead of the front
across mainly east-central and southeast Illinois Monday
afternoon. After that, forecast confidence becomes poor as forcing
decreases and model discrepancies linger. In general, the Tuesday
through Thursday time period will be warm with at least a slight
chance for showers/thunder each day.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1100 PM CDT Thu May 17 2018

VFR conditions to hold into the morning hours and then we should
see lower cigs, low VFR to MVFR category, overspread the forecast
area from south to north during the afternoon hours. Short term
models suggest we may see some scattered showers in the morning
and again later in the day but coverage too limited to include
more than a VCSH at this time. Forecast soundings suggest we may
go into low MVFR or possibly IFR cigs tomorrow night as the weak
storm system shifts north across the region. East to northeast
winds of 10 to 15 kts tonight will be more easterly on Friday with
speeds again in the 10 to 15 kt range.




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