389
FXUS63 KILX 230448
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1148 PM CDT Sat Jun 22 2024

.KEY MESSAGES...

- A decaying line of thunderstorms will push into the area
  tonight. Hazardous weather will not be widespread, but a few
  locations will be susceptible to torrential rainfall,
  lightning, and pockets of gusty thunderstorm winds.

- Afternoon temperatures will average about 5 degrees warmer than
  climatology over the next week, with the hottest day of the
  period coming Tuesday when heat index values could exceed
  triple digits.

- Additional rainfall chances (greater than 50% probability) exist
  by the middle of next week with an attendant severe weather risk
  looming.

&&

.UPDATE...
Issued at 844 PM CDT Sat Jun 22 2024

Current forecast still looks on track with storms moving into the
area, probably after 9 pm. HRRR model seems to have the best
handle on current situation and think it`s best with the forecast
timing of any storms arriving. Besides the watch in effect for
parts of the CWA, did update pops/wx grids to account for slightly
slower timing of precip. New update should be coming our shortly.

Auten

&&

.DISCUSSION...
Issued at 151 PM CDT Sat Jun 22 2024

A quick check on features this afternoon reveals a compact mid-
level shortwave trough pushing across the Upper-Mississippi
Valley, with an attendant cold front extending from Green Bay to
Omaha to Dodge City. A narrow corridor of low-to-mid 70s sfc
dewpoints have pooled ahead of the this front, and convective
initiation is already occuring across portions of NE Iowa. Steep
low-level lapse rates and sufficient surface heating out ahead of
these features should help erode any remaining cap, while a mid-
level speed max (40-50 kts @ 500 mb) nosing in from the west helps
augment deep layer shear. The net effect will be clusters of
organized thunderstorms blossoming and pushing southeastward along
the cold front. CAMs remain in excellent agreement that such
activity will hold together as it sinks into central and southeast
Illinois late this evening.

An attendant severe weather risk remains in tact tonight, mainly
in areas north of a Beardstown-to-Bloomington line where the axis
of a 30-40 kt LLJ will be positioned. Damaging thunderstorm wind
gusts, associated with a mature cold pool, is the main concern by
the time the line reaches our forecast area.  The expectation,
though, is for convective activity to steadily fade overnight as
the upper forcing (shortwave) becomes displaced too far northeast,
the low- level jet axis gradually narrows and pinches off while
convergence along the front weakens. In other words, thunderstorms
will become less organized with southeast extent, and areas south
of I-72 may not see much thunder at all.

Hydro has the potential to steal the show tonight, with a few CAM
members (notably the ARW, NAM Nest, and NSSL WRF) offering localized
amounts up to 3" anywhere north of that Beardstown-to-Bloomington
line. While this won`t be the rule by any means, it`s certainly a
plausible outcome given a healthy LLJ and PWATs along the front
that exceed the 99th percentile of mid-June climatology.

A marginal cool down is anticipated Sunday in the wake of frontal
passage, with afternoon highs mostly in the mid-to-upper 80s. This
will be short-lived, though.

By Monday, mid-level heights will steadily increase beneath a
plume of hot air surging northward out of the western Gulf.
Temperatures on Monday will eclipse 90 degrees in many areas, and
if the deterministic NBM gets close to verifying, Tuesday will
max out in the mid-to-upper 90s ahead of the next frontal zone
with heat index values potentially exceeding 100 degrees. Tuesday
is not necessarily a slam dunk Heat Advisory day, though, with
multiple failure modes in play. Chief among them is a nocturnal
MCS. While this signal is mostly muted in ensemble and multi-
model guidance, the global deterministic do show some semblance
of this possibility with a few shortwaves lurking upstream across
the Corn Belt.

Otherwise, our attention is focused on the frontal passage itself
Tuesday night into Wednesday. Given the very moist and unstable
air mass ahead of the front, its passage may be accompanied by an
attendant severe weather and hydro risk.

Another brief cool down is then anticipated Thursday into Friday
as modified Canadian high pressure settles over the Great Lakes
region. Afternoon highs will mostly be in the upper 80s during
this period. Nevertheless, another signal for hot and increasingly
humid weather returns late next week and into the weekend --
perhaps marking a return to mid 90s heat and an additional round
of thunderstorm activity.

MJA

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1148 PM CDT Sat Jun 22 2024

Convection is finally moving into the CWA and will begin to affect
the TAFs during the overnight hours, beginning around midnight and
continuing for several hours. Tried timing storms at each sites
but only lasting for about an hour. Clouds will be VFR to start
and when the precip moves in, but guidance suggests MVFR clouds
will move in late tonight and last until the mid morning hours.
Thinking 2.5kft is where it will form at, but some models show as
low as 1.5kft. Scattered VFR clouds are expected my mid morning at
all sites, then become clear during the evening. Winds will be
southwest ahead of the storms, but become westerly during the
storms. After the storms, winds will become northwest through the
rest of the TAF period. Speeds late tonight and tomorrow will be
around 10kts.

Auten

&&

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

$$