646 
FXUS63 KILX 181139
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
639 AM CDT Sat Aug 18 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT Sat Aug 18 2018

Areas of fog have developed during overnight across eastern IL,
especially east of I-55 with dense fog at Champaign and Terre
Haute, IN. Effingham had 1/4 mile vsby about an hour ago and now
up to 3 miles. Fog is lighter from I-55 west with mainly MVFR
vsbys in areas, and also lighter in far southeast IL where broken
to overcast mid level clouds lingered. The latest CAM models show
lowest vsbys from Champaign to Shelbyville se early this morning,
so will hit the fog harder in eastern IL through 9 am with areas 
of dense fog, locally dense. CAM models show another area of more 
widespread fog and possibly getting dense over nw IL, generally 
from Sterling and Rochelle nw, and a smaller patch of lower vsbys 
with fog just west of Galesburg and Macomb early this morning. 

Aside from early morning fog, next forecast concern is will there
be isolated convection during this afternoon. Predawn surface map
shows a weak cool front over far southeast parts of IN/IL into nw
AR. Aloft an upper level trof extended from southeast Ontario sw
into the mid/lower MS river valley. Models continue to show a
weaker upper level trof over the Ohio river valley today while
surface front moves slowly se toward the Ohio river/nw KY by 7 pm.
Some weak instability develops this afternoon with CAPES of
1200-1800 j/kg and latest CAM models are showing isolated showers
and possibly a thunderstorm developing mainly east of I-55 this
afternoon, then dissipating prior to sunset. Forecast soundings
show a long narrow band of CAPE se of IL river while not much of 
a lifting mechanism around today. So keeping pops in the 10-20%
range east of the IL river this afternoon. Highs today of 82-86F
with coolest readings in east central IL where fog is more
widespread early this morning and more cumulus clouds appear in
eastern IL this afternoon closer to upper level trof to our east.

Dry weather expected tonight as diurnally driven cumulus clouds
diminish during this evening. Could be some patchy fog developing
again overnight. Lows tonight in the low to mid 60s. 

.LONG TERM...(Sunday through Friday)
ISSUED AT 355 AM CDT Sat Aug 18 2018

Upper level ridging into IL on Sunday along with a weak surface
high pressure settling in should keep it dry and a bit warmer
across the area with more sunshine. Highs in the mid 80s with a
few upper 80s over southern and western CWA. 

A vigorous mid/upper level short wave trof over Idaho will track
into the central Plains by 12Z/7 am Monday and begin to spread
chances of showers/thunderstorms into western CWA overnight 
Sunday night. This storm system then tracks into IL by Monday 
evening and likely brings showers/thunderstorms to the area on 
Monday into Monday evening. Despite some wind shear of 30-40 kts 
on Monday afternoon into Mon night, Some occlusion of this storm 
system and best instability in south of our CWA on Mon 
afternoon/evening and a weak ribbon of instability over MS river 
valley/sw CWA. So chances of severe thunderstorms appears low at 
this time. Precipitable water values peak around 2 inches again 
and supports locally heavy rains. We currently are forecast 
rainfall amounts of 0.70 to 1.10 inches, lowest amounts se of I-70
and highest over the IL river valley. Showers and thunderstorms 
to diminish from the west later Monday night, as upper level trof 
axis shifts east to the IL/IN border by 12Z/7 am Tue. But 
lingering upper level trof over the Ohio river valley Tue will 
keep chances of showers and isolated thunderstorms around on Tue 
especially in eastern IL. Highs Mon in the upper 70s/lower 80s, 
warmest in southeast IL. Highs 75-80F on Tue. 

A pleasant stretch of dry, cooler and less humid weather expected
across central/se IL from Tue night through Friday as the upper 
level trof moves into the northeast states and surface high 
pressure settles into the Midwest and southern Great Lakes. Highs 
in the mid to upper 70s Wed and near 80F on Thu, and lower 80s 
Fri. Lows in the upper 50s to around 60F Tue night and mid to 
upper 50s Wed night and upper 50s to around 60F Thu night. 

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 636 AM CDT Sat Aug 18 2018

Patchy stratus and fog will produce MVFR/IFR conditions across the
central Illinois terminals early this morning, and these low
clouds may return by late tonight. Otherwise, quiet conditions are
expected across the central Illinois terminals, with generally
light northeast winds.

&&

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

$$

SHORT TERM...07
LONG TERM...07
AVIATION...Bak