Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 220745

Area Forecast Discussion
National Weather Service Lincoln IL
245 AM CDT Sat Jul 22 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 245 AM CDT Sat Jul 22 2017

One more brutal day of heat on tap, as widespread heat index
values of 110-115 are likely over a good portion of the CWA this
afternoon. Some thicker clouds along and north of the I-74
corridor may help keep temperatures down a tad, but heat index of
105+ still likely there as well. High temperatures should still
reach the mid-upper 90s, hottest from Jacksonville southeast to

Late night satellite imagery showing several MCS`s from eastern
South Dakotas into central Indiana. Bulk of the rain from these
features has been staying to our north so far, but some storms
will begin moving into the northwest CWA shortly. Latest HRRR
indicates the northern CWA will see the most threat through about
9 am or so. After that, leftover outflows and a weak frontal
boundary settling southward will be the focus for any renewed
development later this afternoon. NAM/GFS continue to show
tremendous instability this afternoon, with CAPE values around
5000 J/kg, although the shear remains weak south of I-74 where
there is more influence from the upper ridge. The front will slow
down as it moves into the southern CWA, so will maintain some
chance PoP`s into the night south of I-72.


.LONG TERM...(Sunday through Friday)
ISSUED AT 245 AM CDT Sat Jul 22 2017

Upper low currently just west of Lake Winnipeg will open up a bit
as it swings into the Great Lakes on Sunday, helping to finally
break down the ridge over the Midwest. Drier air will be a bit
slower to spread into our area, but it currently appears that
with 60s dew points arriving in the afternoon, this should keep
the heat index below 100 degrees in most of the CWA on Sunday.
Thus, will allow the current heat headlines to expire on schedule
this evening.

Cold front is expected to arrive in the northwest CWA during the
afternoon, and push southeast through the evening. Forecast
soundings over the southern CWA are a bit on the dry side, and
have some concerns that the SPC Day2 convective outlook of a
slight risk pushes too far south. The GFS is most favorable for
any strong/severe storms in the southeast CWA, but most of the
other models are dry in the evening over that area.

A couple nice days of drier air on tap, as high pressure drifts
east across the Great Lakes. Unfortunately, the upper ridge
starts to build eastward toward mid week, spreading more 90s back
into the area by Wednesday. Main question will again be with the
placement of the ridge periphery, which is closer to our CWA than
the recent couple days. The GFS is fastest in bringing
precipitation with a frontal boundary southward, as early as
Wednesday afternoon, while the ECMWF is favoring more of a
Thursday arrival with associated rain chances. Late in the week,
both models favor more of a ridge position over the Rockies into
the first part of the weekend, returning temperatures close to


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1225 AM CDT Sat Jul 22 2017

Large convective complex from northeast Iowa into northern Indiana
has largely been tracking north of the central Illinois TAF sites
this evening. Outflow boundary from them should be passing through
KBMI very soon with some temporary northwest gusts of 20-30 knots
or so, and the TAF was amended for this possibility. Highest gusts
will likely be before 06Z, so the TAF starting at 06Z will only
have some north gusts of 20-25 knots for a couple hours. Have also
maintained the VCTS mention at KPIA/KBMI from about 08-14Z as the
storms track southeast from Iowa. In addition, have added LLWS
mention during that time for these two sites with a lower level
jet ramping up just south of the convection.

After that, mainly quiet conditions expected through the
afternoon. A cold front will be moving through late afternoon and
evening between about 22-03Z. Some scattered storms possible along
this boundary, but too uncertain to add at this point.


Excessive Heat Warning until 8 PM CDT this evening for

Heat Advisory until 8 PM CDT this evening for ILZ030-031-038-



SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart is the U.S. government's official web portal to all federal, state and local government web resources and services.