658
FXUS63 KILX 060320
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1020 PM CDT Fri Jul 5 2024

.KEY MESSAGES...

- Scattered showers and storms return late Sunday through Tuesday,
  with the highest chances being Monday afternoon (40-60% chance).
  Severe thunderstorms and flash flooding are unlikely.

- Temperatures will be seasonable over the next week, with highs
  in the 80s and lows in the 60s. Significant heat impacts are
  not expected during this time.

&&

.UPDATE...
Issued at 805 PM CDT Fri Jul 5 2024

00z upper air data showed an upper low spinning north of the Great
Lakes. A few weak shortwaves were noted on water vapor imagery southwest
of the low, producing isolated instability showers as far south as
Knox and Stark counties. These will fade over the next hour due to
the loss of diurnal heating. At the surface, low pressure was
analyzed over eastern lower MI, with a ridge over the central
Plains. As these features shift east overnight, light west winds
and mostly clear skies will prevail locally. Gusty west-northwest
winds this afternoon advected a slightly drier airmass in, with
lower 60s dewpoints. This will promote lows several degrees cooler
than recent nights, mainly in a 60-65F range.

25

&&

.DISCUSSION...
Issued at 149 PM CDT Fri Jul 5 2024

A slow-moving low pressure system continues to drift SE over WI.
The associated cold front has pushed into IN as of 120pm/1820z,
with a few showers lingering near the IL/IN stateline at this time
with the expectation that these will shift east in short order.
Otherwise, brisk west-northwest winds prevail across the area with
gusts of 20- 25 mph. Diurnal Cu is still expected to increase in
coverage this afternoon/early evening (at least north of I-72) as
forcing associated with the upper low pivots into the area.
Regional radar shows scattered showers across IA where weak
instability is present, and both sfc obs and mPING reports
indicate rain reaching the sfc. Maintained a slgt chnc (15-20%) of
rain in areas mainly north of Peoria. The diurnally-driven cloud
cover should fade after sunset, resulting in mostly clear skies
overnight. No weather impacts are expected on Saturday as the
post-frontal airmass remains in place and weak sfc high pressure
drifts across the Ozarks. Temperatures will be near to slightly
below normal, with highs in the low to mid 80s.

Into Sun, an amplified upper ridge will be centered over the
western US, while a trough deepens over the central Plains and
Beryl (presumably a Hurricane) approaches the S TX/N Mexico
coasts. Locally, much of the area should stay dry Sun, although a
few storms are possible (mainly west of the IL River) during the
late evening/overnight hours (20-30% chance). Forecast soundings
show modest instability (1000-1500 J/kg), but weak deep layer
shear below 30 knots should limit storm organization.

Better precip chances arrive on Mon (40-60% chance) and linger
into Tues as a cold front moves through the CWA. Evaluating where
Beryl will make landfall is beyond the scope of our local
forecasting needs, but ensemble members are in strong agreement
that the presence of the trough over the Plains/Midwest will tug
the remnants of Beryl northward across interior E TX early next
week. While Beryl may enhance moisture advection ahead of the
front, even the fastest/northernmost ensemble members have Beryl
far enough removed from our area that the truly tropical airmass
does not interact with the front. Further, the presence of Beryl
over the southern Plains actually appears to play a limiting role
in the local severe storm potential from this early week trough.
While the 500mb flow increases across central IL as the trough
deepens (resulting in greater than 30 knots of deep layer shear),
the flow pattern from Beryl disrupts the elevated mixed layer
(EML) advection out of the SW US, and thus mid-level lapse
rates/instability values are progged to be quite lackluster.
Machine-learning guidance suggests that severe storm or flash
flooding potential are both less than 5% Sunday through Tuesday.
The probability of exceeding 0.5" of rain through Tuesday AM is
just 15-30% (highest west of the IL River).

Beyond Tues, most guidance has the cold front stalling south of
our area, but given the typical model spread in placement at the
Day 6+ range there is enough uncertainty to warrant keeping
occasional slgt chnc (less than 25%) PoPs in the extended
forecast. As the remnants of Beryl are absorbed into the main jet
stream, most guidance has the remnants tracking south of the Ohio
River, but this could be close enough to provide some additional
forcing for showers/storms during the latter half of the work
week. Throughout the period, temperatures are forecast to be
seasonable, with highs in the 80s and lows in the 60s.

Erwin

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1020 PM CDT Fri Jul 5 2024

High pressure currently over the central Plains will shift east
over the next 24 hours, bringing west winds near/under 10 kt, then
going calm Saturday evening. Diurnal cu will redevelop Saturday
morning and current high resolution models suggest a few hours of
broken MVFR ceilings at KBMI-KCMI before rising above 3k feet by
midday. Terminals farther west and south should see bases form
near 3k feet then rise through late morning, but will watch trends
for a short window of MVFR ceilings at these sites as well.

25

&&

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

$$