Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 270532

Area Forecast Discussion
National Weather Service Lincoln IL
1232 AM CDT WED JUL 27 2016

Issued at 908 PM CDT Tue Jul 26 2016

An outflow boundary from convection to the south of our forecast
area has advanced north toward our southern counties. It was
responsible for a few funnel cloud reports near St Louis.
Convection along that boundary has generally weakened in the last
hour, as the storms from east of St. Louis have drifted to the
E_NE toward Effingham and Clay counties. We already have slight
chances of storms across our counties south of I-70, and that
should suffice for now. The operational HRRR, RAP, and NAM12 show
some storms possibly progressing northward into Sangamon and
Christian counties later this evening, but other HRRR and ARW runs
keep those counties dry the rest of the night and confine any
convection to mainly along HWY 50 across our far southeast 3
counties. Will not expand PoPs northward just yet, based on radar

We appear to have had enough clear skies north of I-70 to mix some
drier air down toward the surface, helping to alleviate fog
formation later tonight. More persistent cloud cover south of I-70
kept surface dewpoints higher due to limited mixing from the dry
mid-layers. Will keep only fog mention south of I-70 later
tonight. The latest HRRR has become more optimistic with higher
visibilities late tonight, so fog potential may be decreasing
across the board.

Low temps tonight appear on track for the mid to upper 60s in most
areas, with low 70s south of Effingham to Lawrenceville.

No major changes needed with tonights forecast, so no formal zone
update will be needed. The minor edits are already available


.SHORT TERM...(This evening through Wednesday)
ISSUED AT 252 PM CDT Tue Jul 26 2016

18z/1pm surface analysis shows stationary frontal boundary along the
Ohio River, with 1018mb high centered further north across southwest
Wisconsin.  A cluster of thunderstorms with heavy rain that rolled
along the I-70 corridor earlier this morning is now well to the east
across southern Ohio, while additional scattered convection is
developing further west along the front from southern Illinois into
the Ozarks.  Based on radar trends and latest HRRR guidance, it
appears any convection that occurs for the remainder of the
afternoon into the evening will stay south of I-70.  Have therefore
gone with a dry forecast through tonight across much of the KILX
CWA, with low chance PoPs confined to the far SE.  With mostly clear
skies and light winds expected, there is some concern for fog
overnight.  A few high-res models are suggesting widespread
visibility reductions, while others are showing little or no fog.
Given what happened last night and the fact that ample boundary
layer mixing is taking place today, have opted to keep fog out of
the forecast except along/south of a Paris to Shelbyville line where
recent rain this morning has provided additional low-level moisture.
Once any early morning fog dissipates, partly to mostly sunny
conditions can be expected on Wednesday.  With frontal boundary
still in place just to the south, cannot rule out a few showers and
thunderstorms along/south of I-70 where low chance PoPs remain in
the forecast.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 252 PM CDT Tue Jul 26 2016

Surface boundary south of the area will begin to move northward late
Wed night and bring the chance of thunderstorms back into
southeastern IL Wed night. In addition, as a ridge builds in the
central plains, the boundary will get pushed east into the MO valley
and across Iowa. Thunderstorm chances will increase in western IL
and northwestern IL associated with the advancing boundary. By Thur,
a surface low pressure area will begin to move along the boundary
and into IL. This will continue the threat of showers and
thunderstorms through Friday. As the low pressure area moves east, a
cold front will get dragged through the area. By Friday night, the
front will be south of most of the CWA, but the chance for
thunderstorms will likely linger in the eastern part of the state
through Saturday.

Remainder of the extended period should be mainly dry, except for
Monday in southeast IL. However, the blending of all the models
keeps a slight chance of precip in the area Sat night through Sun
night...and then again Monday night and Tuesday.

Temps through the period will be in the lower to middle 80s.
However, by the end of the current forecast period, above normal
temps will begin to advect toward the area starting Tuesday as
ridging in the plains edges toward the mid west.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1232 PM CDT Tue Jul 26 2016

Main concern this TAF period is for potential of MVFR conditions
in fog later tonight. Guidance numbers are hitting fog pretty hard
at all TAF sites, but have tempered that back to just tempo/s for
MVFR from 11z-13z. Mixing will start shortly after sunrise,
helping to clear out any fog. High pressure will continue to build
into Illinois on Wednesday, with lower dewpoints hopefully mixing
out some of the residual moisture. FEW to SCT CU will develop
tomorrow morning, with less CU in the east than west. Winds will
remain light east-southeast tomorrow, with speeds less than 10kts.


.ILX Watches/Warnings/Advisories...


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