Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271936
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
236 PM CDT SAT AUG 27 2016

.SHORT TERM...(This evening through Sunday)
ISSUED AT 236 PM CDT Sat Aug 27 2016

18z/1pm water vapor imagery shows a distinct fetch of deep-layer
moisture flowing northward from the western Gulf of Mexico into
Missouri and west-central Illinois.  While the synoptic warm front
has lifted well to the north into southern Wisconsin, outflow
boundaries left behind by early morning convection will likely serve
as the focusing mechanisms for additional thunderstorms within this
moisture axis later this afternoon and evening. HRRR/WRF-NMM/WRF-ARW
have all been consistently showing scattered convection developing
mainly across the western half of the KILX CWA after 21/22z...with
the storms then gradually dissipating by mid-evening.  As a result,
will continue to focus low chance PoPs west of I-57 this afternoon
and evening, with just slight chance further southeast.  Once
daytime instability wanes, only isolated showers/thunder will linger
overnight.  With skies partially clearing, winds becoming very
light, and ample low-level moisture in place, think fog will develop
overnight.  HRRR is showing fog becoming prevalent after midnight,
while both NAM and GFS forecast soundings point to fog development
as well.  It is difficult to pinpoint exactly where the fog will
become most widespread/dense, but think this may be focused over the
Illinois River Valley where heavy rainfall occurred earlier this
morning.  At this point, will include patchy fog mention everywhere,
but this may need to be boosted by later shifts as trends become
more apparent.  Once any early morning fog dissipates, another
partly sunny, warm, and humid day will be on tap for Sunday.  With
very little focus for convection present, will once again only carry
20-30 PoPs.  High temperatures will top out in the middle to upper
80s.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 236 PM CDT Sat Aug 27 2016

A broad subtropical high pressure ridge will be in the process of
building by Sunday evening promoting a storm track to the north of
central IL as 500 mb height gradients and stronger westerly flow
become confined to the northern tier of states and southern Canada.
Central IL looks to remain in an air mass characterized by 1.5 to
2.0 inches precipitable water and afternoon MLCAPE instability
values around 1500-2000 J/KG through Tuesday. With the flow aloft
weak, organized or severe storms are not expected although isolated
to scattered afternoon/early evening showers and thunderstorms will
be possible. Expect highs in the mid 80s to around 90 with the
cooler temperatures along I-74 and the warmer temperatures south of
I-70. Dewpoints in the lower 70s will bring heat index values around
90 to 95 each afternoon. Lows upper 60s to around 70.

As an upper level trough develops over the northeast U.S. and
northwest flow develops over the upper Midwest...a cold front
continues to be advertised by the 12Z model runs...pushing southward
into the Midwest. For Wednesday afternoon the front could trigger
scattered thunderstorms as it moves into central IL. Highs will
depend on exact timing, but have estimated low to mid 80s for now.
Wednesday night and beyond dry conditions can be expected as cooler,
stable, and dry air push into the area with high pressure and
subsidence predominating. Expect highs in the upper 70s to lower 80s
with a slow warming trend through the period. Dewpoints in the low
to mid 60s will make conditions considerably less humid. Lows
expected to range from the upper 50s to lower 60s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1244 PM CDT Sat Aug 27 2016

Skies have partially cleared across much of central Illinois early
this afternoon: however, a patch of MVFR ceilings persists at both
KPIA and KBMI. Based on satellite trends and NAM forecast
soundings, think these lower clouds will scatter over the next 1-3
hours. As the atmosphere destabilizes, scattered thunderstorms
will develop along old outflow boundaries later this afternoon and
evening. The HRRR has consistently focused the convection
along/west of I-55 after 21/22z. Radar imagery remains clear at
the moment, but this will be the area to watch later today. Have
included VCTS at KPIA between 21z and 02z...then further east to
KCMI between 22z and 03z. Any storms that fire later this
afternoon will dissipate by mid-evening. Due to partial clearing,
winds becoming very light, and ample low-level moisture being in
place, think fog will develop tonight. Hard to pinpoint exactly
where the fog will become most prevalent, but will hit visbys
hardest at KPIA where heavy rainfall occurred earlier this
morning. Have taken visbys down to 2 miles at KPIA after
09z...and around 3 miles at the remaining terminals.


&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

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


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