Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 221753
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1253 PM CDT Sat Jul 22 2017

.UPDATE...
Issued at 1039 AM CDT Sat Jul 22 2017

Decaying storm complex dropped into central Illinois this morning,
bringing clouds and some much needed rainfall to the northern half
of the KILX CWA. 15z/10am radar imagery shows a quickly
dissipating area of showers lingering across east-central
Illinois, mainly along and east of a Monticello to Shelbyville
line. Based on rate of dissipation, as well as latest HRRR, think
the showers will be completely gone in 1-2 hours. Clouds will
linger a bit longer, but will also clear out by early to mid
afternoon. Once the sun returns, rain-cooled temperatures in the
70s will quickly recover into the lower to middle 90s by late in
the day. Made some updates to hourly temps and lowered afternoon
highs into the lower 90s across the NE CWA where clouds will
persist the longest. With temperatures once again climbing into
the 90s and dewpoints hovering in the middle to upper 70s, heat
index values will peak from 105 to 110 degrees this afternoon. Could
see some widely scattered convection later this afternoon as a
cold front approaches the region, with the greatest coverage
across the NE CWA into central Indiana.

&&

.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
Effingham.

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
normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1253 PM CDT Sat Jul 22 2017

Cloud cover from early morning convection has largely dissipated,
with some lingering mid/high clouds noted on latest visible
satellite imagery. A cold front will sink southward into the
region later this afternoon, triggering widely scattered
thunderstorms. Based on latest high-res models, have introduced
VCTS at KPIA/KBMI after 21z...then further south at KSPI/KDEC
after 23z. Any late afternoon/evening storms will dissipate after
dark...followed by dry conditions overnight into Sunday morning.
Winds will initially be S/SW at around 10kt, then will veer to the
N/NW tonight in the wake of the cold front. Despite FROPA, plenty
of boundary layer moisture will linger, so think patchy fog will
be possible late tonight. Have lowered visbys to around 5 miles
after 09z accordingly.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT this evening for
ILZ027>029-036-037-040>042-047>054-061-062-066>068-071>073.

Heat Advisory until 8 PM CDT this evening for ILZ030-031-038-
043>046-055>057-063.

&&

$$

UPDATE...Barnes
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Barnes



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