338
FXUS63 KILX 291747
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1247 PM 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.

&&

.UPDATE...
Issued at 1007 AM CDT Sat Jun 29 2024

After a couple morning thunderstorms, some breaks of sunshine across
much of the ILX CWA is allowing radiational warming to bring temps
up quickly (not that we were particularly cool to begin with) into
the mid 80s already by 10am. The airmass in place is
characterized by mid 70s dew points, with a PWAT of 2.17 inches
and 3344 J/kg MUCAPE on the morning raob - more than sufficient
instability for heavy thunderstorms. Fortunately, low-mid level
warm advection from the west later this morning into early
afternoon will strengthen the cap evident on the morning sounding,
limiting potential for convection except with the cold front,
along which a few CAMs are suggesting convection will develop
between 4 and 6pm...sliding east and out of our area by 11pm. At
this point, the greatest model agreement in storms during that
time period is near and east of a Bloomington to Effingham line,
where HREF neighborhood (radius = 20 km) probabilities for >40dBZ
surpass 50%.

Bumgardner

&&

.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 18z TAFs through 18z Sunday Afternoon)
Issued at 1241 PM CDT Sat Jun 29 2024

Scattered thunderstorms have developed early, courtesy of a weak
boundary and a bit more sunshine than expected which eroded our
capping inversion. DEC and CMI have already reported
thunderstorms, which should be moving out of the area in the next
hour or two. Additional development is less certain given the
strengthening cap further west, though wind shear will be
increasing along the cold front as it moves southeast through the
area late this evening. Given expected limited coverage (30-50%)
along that front and continually shifting model output, we`ve
included a prob30 for a few hours (roughly 22z Sat to 02z Sun, or
5-9pm CDT) this evening to message that potential, which is
highest once again at CMI and DEC. Behind the front, an abrupt
shift and uptick in winds is forecast with frequent gusts near or over
20 kt expected for several hours before winds gradually become
more steady around 10-13 kt toward Sunday morning.

Bumgardner

&&

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

$$