520
FXUS63 KILX 291038
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
538 AM CDT Sat Jun 29 2024

.KEY MESSAGES...

- Scattered thunderstorms may redevelop this evening along a cold
  front, though the probability is low (< 30% chance). If storms
  do redevelop, they could carry an attendant severe risk with 60
  mph wind gusts and quarter-size hail.

-  A stretch of drier, cooler and less humid weather will arrive
   late tonight and span through Monday. Sunday night lows will
   dip into the upper 40s in some spots.

-  A surge of seasonably hot and humid conditions returns by the
   middle of next week with daily chances for thunderstorms
   Wednesday - Friday.

&&

.DISCUSSION...
Issued at 1242 AM CDT Sat Jun 29 2024

Overnight thunderstorm activity was limited by an upstream MCS in
central Missouri, and we begin today with plenty of convective
debris overhead. With a MCV tracking along I-70, it`s unlikely
that we get enough sunshine to erode CINH this afternoon. Any
convective initiation that occurs is going to have to do so this
evening on the cold front.

Up until this point, CAMs had been lackluster on the convective
potential later today, but the 06z HRRR is now resolving a line of
storms pushing southward along the front after 21z/4pm. Deep-layer
shear (< 30 kts) should limit an organized/widespread event, but
moderate instability (2500-3000 J/kg MLCAPE) and dry air
entrainment could result in a few pulsey updrafts capable of large
hail and strong downbursts. As with any conditional threat,
convective trends will need to be monitored throughout the day.

Anomalous surface high pressure will settle into the Northern
Plains tonight, gradually building into the Great Lakes region by
Sunday night. Seasonably cool temperatures will accompany this
modified Canadian airmass, yielding afternoon highs in the mid-
to-upper 70s and overnight lows in the 50s. A few spots may even
dip into the 40s Sunday night. Record low temperatures are not in
serious jeopardy of being broken, but an impressive cool down
nonetheless.

Temperatures bounce warmer by Tuesday as low-level winds veer
southwesterly behind departing surface high pressure. Typical
summertime heat and humidity will then pool ahead of a cold front,
which is forecast to drop through the region Tuesday night into
Wednesday. Mid-range guidance remains in fair agreement of the
surface front washing- out over the area Wednesday night as the
main upper-level forcing becomes displaced too far to the
northeast. This stalled-out front may provide a focus for heavy
rainfall with the synoptic pattern bearing some resemblance to a
Maddox setup for flash flooding, with slow 850-300mb flow (30
kts) and multiple shortwave impulses running parallel to the
surface front in an environment where PWATs eclipse the 99th
percentile of early July climatology for 24 hours.

Notable spatial/timing differences among blended and ensemble
guidance with respect to frontal passage are causing the NBM to
smear chance PoPs (40-60%) through much of the midweek period,
with a signal for drier weather returning by next weekend.

MJA

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 530 AM CDT Sat Jun 29 2024

Upstream obs reveal MVFR cigs spreading into the region ahead of
the synoptic cold front. Have timed this to arrive to the central
Illinois terminals by 14z. Short-term guidance then suggests cigs
lift back to VFR by 19z as a tongue of dry air mixes in from the
west. As a cold front sags into the region this evening, have
introduced VCTS for a couple hours beginning at 22z. A cooler and
much drier air mass begins to build across the terminals
overnight, with winds veering north behind the front and skies
becoming clear.

MJA

&&

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

$$