813 
FXUS63 KILX 130430
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1130 PM CDT Thu Jul 12 2018

.UPDATE...
Issued at 903 PM CDT Thu Jul 12 2018

Central Illinois will remain under the influence of high pressure
tonight into Friday, despite the high's gradual departure to the 
east over the next 24 hours. Minimal cloud cover is expected
across the area tonight, and much of the day tomorrow. A line of
storms well to the north-northwest of Illinois could send some
cirrus clouds our way. Otherwise, mostly clear skies are expected
tonight and sunny skies for most of tomorrow. A few storms will be
possible in far western IL later tomorrow afternoon, but those
storms should remain west of our forecast area for the most part.

Southerly winds at 5-10 mph will cause our low level moisture to
increase, with dewpoints climbing into the 70s tomorrow. The
higher dewpoints will create rather muggy conditions tonight and
tomorrow, with tomorrow's heat index readings climbing to around
100F. 

The current forecast looks in good shape, and no formal updates
will be needed this evening.

&&

.SHORT TERM...(This evening through Friday)
ISSUED AT 303 PM CDT Thu Jul 12 2018

High pressure will keep the weather mild and hot through the short
term. Southerly flow at the surface on the back side of the ridge
will continue to push warm and muggy air into the region, with the
dewpoints already in the upper 60s/low 70s. Some scattered high
clouds from the MCS to the north today has done little to impede
the afternoon temperatures, and will likely not do much to impede
tomorrow. With high temperatures once again climbing into the 90s,
the heat index values will be in the upper 90s/near 100F tomorrow. 

The remainder of the forecast revolves around the outflow/frontal
boundary developing to the north settling into the region over the
next couple of days. The pattern is one that is similar to a few
runs already this season, and a reasonable amount of confidence in
the scenario initially...even if the details are clouded going 
into the next week. 

.LONG TERM...(Friday night through Thursday)
ISSUED AT 303 PM CDT Thu Jul 12 2018
Friday night, the developing boundary to the north will likely be
further strengthened by convection/cold pool/outflow as it slowly
settles into the mid Mississippi River Valley. Temps/dewpoints
push the heat index values very close to advisory criteria for
Saturday, should the diurnal swing not get interrupted by cloud
cover/convection in the north. But the pops have sped up in the
early hours Saturday, and those high heat index values may be
patchy depending on where initiation starts... so for now,
avoiding headline specificity. SPC has the area in a general
thunder at this point, arguably for the same lack of focus for
detail. A wet and unstable airmass will likely need very little
for rapid development once lifted. But similarly to recent
past...there is no shear in a pattern dominated by an upper ridge
over the southern half of the CONUS to sustain any widespread
severe threat at this time. Will depend highly on any mesoscale
features from activity leading up to Saturday morning. And the
threat will decline considerably if that activity develops early
ahead of max heating.

Beyond Sat/Sat night, the boundary slows over the region, and the
NAM/GFS/ECMWF are all pulling weak waves over the boundary aloft,
keeping pops in the forecast for the remainder of the weekend and
through Monday. ECMWF/GFS quickly starts to show signs of some 
convective feedback after the initial front, however, so there may
be more breaks in Sunday/Sunday night than currently in the
blended forecast. Monday will be the next best chance for pops as
a second front finally sweeps through the area, with slightly
cooler temps in place for midweek.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1129 PM CDT Thu Jul 12 2018

No concerns to aviation are expected during the 06z TAF period.
High pressure will remain the primary influence on the area
weather. Cirrus clouds will become thicker after 00z tomorrow as a
line of storms pushes into far W IL. However, no rain or storms
are expected to reach as far east as PIA by 06z tomorrow night. 

Winds are steady from the southeast late this evening, and should
remain SE until sunrise tomorrow. As high pressure continues to
depart farther away to the east, winds will become southerly
tomorrow morning. Sustained winds should remain less than 10kt.

&&

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

$$

UPDATE...Shimon
SHORT TERM...HJS
LONG TERM...HJS
AVIATION...Shimon