Area Forecast Discussion
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FXUS63 KILX 261155

Area Forecast Discussion
655 AM CDT Tue Aug 26 2014

.SHORT TERM...(Today and tonight)

One more hot and humid day is on tap for at least the southern half
of the KILX CWA, as heat index readings climb into the 105 to 110F
range during peak heating. The heat warning will continue from
Lincoln and south, with the heat advisory east to Champaign/Danville
through early evening.

Last evening some cooler air was pushed out from a line of storms
that clipped our north from Stark County to Champaign/Vermilion
counties and south along the Indiana border. That worked to lower
dew points across the north, which should help to keep the heat
indices a bit lower during the afternoon, but still hot in the
upper 90s.

Once again the high-res models are having a hard time with current
convection and are all over the board with respect to storm
development over the next 24 hours. When merged with the lower
resolution models, the general theme is for a line of storms to
eventually develop across our northern counties as a cold front
slowly moves south into our forecast area. A few storm cells
developing in eastern Iowa over the last hour has increased some
confidence that a few storms could affect our northwestern counties
by mid-morning, so will keep at least chance PoPs NW of Peoria this
morning. The daytime storms are projected to drift south as they
dissipate toward I-72 later this afternoon. The next complex of
storms is projected for later tonight, when a stronger MCS is
forecast to roll out of Iowa. Under that scenario, storms would
affect areas north of Peoria after 08z/2am CDT, where we have likely

There remains a high level of elevated instability, with plenty of
precipitable water, so any storms that can overcome the mid-level
warming could produce some very heavy rainfall and strong winds over
the next 24 hours.


.LONG TERM...(Wednesday through Labor Day)

Upper ridge will be breaking down on Wednesday as a wave moves
through the upper Great Lakes region. Still watching the deep trough
seen on water vapor imagery across the western U.S. this morning.
Last couple model runs had some reasonable agreement with tracking
this feature into the Plains by early Saturday, but have some
disagreements resolving the split flow over the central U.S. as a
trough digs over the Pacific Northwest. The ECMWF largely dampen out
the Plains wave, while the GFS keeps it somewhat intact and lifts it
into Wisconsin on Sunday, possibly due to some feedback issues. Have
leaned the holiday weekend forecast more toward the ECMWF as a

In the nearer term, the 00Z models largely bring the front through
most of the forecast area by Wednesday evening, with the NAM
furthest north and the GEM/GFS furthest south. Best shower/storm
threat will be during the morning before the precipitation is
shunted into what`s left of the ridge. After that, focus shifts to
our northwest as the front lifts back northward in response to the
wave moving onto the Plains. Frequent MCS activity will lead to
potential flooding concerns across Iowa/Wisconsin, with mainly
scattered activity in our area from the remnants of said activity or
other development along the boundary.

Rather humid conditions expected to continue on Wednesday, until
drier air spreads in from a high pressure building into the Great
Lakes. However, the humidity will return on Thursday as the front
lifts back north. Temperatures across the southeast CWA may still
reach the lower 90s Wednesday and Thursday, but highs in the 80s
will prevail through the period.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)

A cold front will progress into central IL this afternoon.
Scattered thunderstorms are expected near the front, especially
this afternoon. PIA and BMI could see a few showers and possibly
storms after 15z this morning. The high res models have varying
solutions, with the RAP showing a line of convection across
central IL already at 12z this morning, which is not occurring.
The HRRR holds off storms until 16z near PIA/BMI, with additional
storms behind the cold front this afternoon.

The lower resolution NAM/GFS/Canadian/ECMWF have varying
precipitation patterns over the next 24 hours as well. Overall,
will stick with afternoon storms near the cold front at all TAF
sites. There is some agreement that after midnight tonight,
an MCV will roll out of Iowa into NC Illinois, triggering the next
round of storms. Those would affect PIA and BMI mainly, based on
the expected storm track.

Winds will start out south-southwest ahead of the cold front. By
afternoon, northerly winds will develop behind the front
progressively from PIA to BMI to CMI. The frontal motion will slow
down by this evening as it stalls out over SPI/DEC. Winds at those
sites could just become variable for much of the night.


EXCESSIVE HEAT WARNING until 7 PM CDT this evening FOR ILZ042-

HEAT ADVISORY until 7 PM CDT this evening FOR ILZ043>046-055-057.



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