505
FXUS63 KILX 120350
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1050 PM CDT Thu Jul 11 2024

.KEY MESSAGES...

- Periodic thunderstorm chances will continue into the middle of
  next week, with most of the focus through Tuesday across the
  north half of the state. Severe weather prospects will be
  highest beginning on Sunday.

- Heat and humidity increase this weekend and will likely peak on
  Monday, though 100-degree heat index values may arrive as early
  as Saturday west of I-55.

&&

.UPDATE...
Issued at 804 PM CDT Thu Jul 11 2024

Low level convergence zone along the I-74 corridor where dew
points were pooling around 70 degrees has been the focus for
scattered showers and thunderstorms much of the afternoon and
evening. 00Z ILX sounding sampled steep low level lapse rates (8.0
C/km in the 0-3km layer) which coupled with steep 0-3km MLCAPE of
175-200 J/kg have contributed to favorable conditions for a
number of funnel clouds to form across central Illinois. This
threat should diminish over the next hour or two as the sun sets.
In addition, a number of outflows have kicked well south of the
I-74 corridor allowing convective coverage to diminish. As we head
into the overnight hours, focus will turn to fog development with
recent rainfall contributing to saturated ground conditions and
generally favorable radiational cooling setup expected near the
surface ridge axis.

Deubelbeiss

&&

.DISCUSSION...
Issued at 307 PM CDT Thu Jul 11 2024

Satellite and radar show clouds and scattered showers rotating
along a weak surface boundary, which was analyzed roughly along a
line from Quincy to just north of Indianapolis. Greatest
concentration of showers has been north of the boundary, in an
area best highlighted by the morning NAM Nest run. Precipitable
water values over 1.5 inches continue to support locally heavy
rain as being the primary concern the remainder of the afternoon,
though a few funnel clouds near the boundary can`t be ruled out,
as evidenced by a recent report just south of Champaign. Most of
the showers will be diurnal and fade with sunset, though they may
linger further into the evening south of I-70 as the boundary
settles southward.

The persistent upper trough over the Great Lakes and mid-
Mississippi Valley will remain a focus during the start of the
weekend, but will gradually lift out as high pressure over the
southwest U.S. oozes eastward. Convective concerns begin to shift
to nocturnal thunderstorm complexes, and how far south they will
push. Main storm track will be over the northern Dakotas into the
Great Lakes region, though MCS`s may drop as far south as our
area early next week, as hinted by the GFS/European models. SPC
convective outlooks for Sunday and Monday highlight areas just to
our north, though scattered storms Saturday afternoon may be
strong or locally severe down here (level 1 risk). However,
machine learning outlooks from Colorado State University show a
continued potential through Tuesday. By mid week, more of a
southward push in rain chances will take place, as a deep trough
swings across the Great Lakes region.

Looking at the heat, prospects are increasing for 90 degree
temperatures as early as Saturday, assuming the MCS and associated
cloudiness are not an issue. However, core of the heat still looks
to be Sunday through Tuesday, with heat index values above 100
degrees each day. NBM and WPC guidance highlight best prospects
for heat index over 105 degrees to be on Monday, highest across
the Illinois River valley. The heat breaks on Wednesday as the
cold front pushes southward, and the new CPC 6-10 day outlook
favors below normal temperatures for the following weekend.

Geelhart

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1049 PM CDT Thu Jul 11 2024

A few isolated showers persist across central Illinois, but they
will continue to taper off with dry conditions likely the
remainder of the period. Fog development is expected overnight and
should reduce vsby to at least MVFR if not lower, though
confidence in IFR is low at this time. Fog should dissipate by mid
morning with VFR conditions the remainder of the period. Winds
will be light, less than 10 kt, through the period.

Deubelbeiss

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$