765
FXUS63 KILX 120735
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
235 AM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Most of the area will be dry today, but occasional thunderstorm
  chances exist through Tuesday, some of which could be severe.
  Much of this activity will be focused across the northern half
  of the state.

- Hot and humid conditions build Saturday through Tuesday, with
  highs in the upper 80s to mid 90s, and peak heat indices in the
  upper 90s to 100s.

- A cold front moves through mid-week, providing another chance of
  thunderstorms followed by relief from the heat, with below
  normal temperatures favored during the latter half of the week.

&&

.DISCUSSION...
Issued at 231 AM CDT Fri Jul 12 2024

Upper-level troughing remains in place across the upper Midwest
early Fri AM, with a secondary vort max present near the MO/KS
border. Elsewhere, strong upper level ridging persists over the
western US with 500mb heights approaching 5980m. In the immediate
short-term, fog development is the main concern. Shower activity
(and the associated cloud debris) have waned quickly after
midnight, leaving light winds, mostly clear skies, and moist soils
courtesy of the rainfall from Beryl as well as several rounds of
convective activity in the 48 hours since Beryl departed. As of 1
AM Fri, locations from Paris to Effingham and southeast had
occasionally reported visibility reductions as low as 2 miles,
with lower visibility (including some as low as a quarter mile)
further east in Indiana. 00z HREF guidance had a 50% chance of vis
below 1 mile across much of the CWA, and some HRRR runs have
shown patchy dense fog development. Confidence in the development
and placement of any dense fog is too low to warrant a special
weather statement or dense fog advisory at this time, but will
continue to monitor obs/satellite this morning.

Over the next several days, occasional thunderstorm chances (some
of which could be severe) exist. However, with rather nebulous
forcing mechanisms in play and disagreement between the CAMs,
forecast confidence is low. First, that aforementioned secondary
vort max should progress towards the MO Bootheel today. That could
aid scattered precip development, though the favored region for
this is south of our CWA, and that is reflected in the CAMs. Kept
some low chnc PoPs (15-20%) south of I-70, but the rest of the CWA
is favored to stay void of precip today.

Late Fri night into Sat AM, models depict scattered precip
developing via WAA as well as convergence at the leading edge of a
weak LLJ. There is significant variability in the placement of
this precip, with some models focusing it across central IL while
others keep precip well removed from the ILX CWA. During the day
Saturday, continued southerly flow will result in warm/moist
advection, which when combined with moderate mid-level lapse rates
will result in strong instability. The Grand Ensemble depicts a
60%+ chance of 2500 J/kg of surface-based instability west of
I-55. However, deep layer shear is marginal at best, and there is
a capping inversion that would need to be overcome and limited
forcing to do so. Models are quite limited in their convective
coverage Sat evening. Deeper into the period, disturbances riding
around the upper ridge could result in repeated MCS activity each
night Sat through Mon, but guidance continues to suggest the most
likely area for this MCS activity is north of I-80. If this
activity were to track into the ILX CWA, the continued presence of
strong instability would support some severe storm potential,
although deep layer shear continues to appear weak this far south
as the upper flow weakens.

Barring precip or cloud cover from MCS activity, hot and humid
conditions are expected, especially on Sun-Mon. Between continued
southerly flow advecting gulf moisture northward as well as
moisture from recent rains and developing crops, afternoon
dewpoints are on track to reach the mid 70s. With the moist
conditions resulting in solar energy being consumed for
evaporation, the NBM forecast high temps may be running a tad
hot, but at any rate the combination of heat and humidity are
expected to push heat indices to uncomfortable levels. If the
current forecast holds, a heat advisory will need to be considered
for Sun-Mon, when peak heat indices are forecast to be push near
or over 105 degrees.

Confidence in precip chances increases as a cold front moves
through the CWA, with most indications that this occurs during
the Tues night-Wed time frame. Due to timing differences in the
models, the NBM has 20-40% chance PoPs spread over a broad time
range (Tues- Thurs). As confidence increases regarding the timing
of this front, expect PoPs to be refined and focused over a much
smaller time period. During the latter half of the week, following
the cold FROPA, upper ridging over the western US amplifies, with
the grand ensemble depicting a 90% chance for 500mb heights to
exceed 5940m over the Four Corners region. That subsequently
results in troughing over the Great Lakes/Upper Midwest, and below
normal temperatures are favored (40-60% chance) across IL from
Wed into next weekend.

Erwin

&&

.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.
&&

$$