628
FXUS63 KILX 131150
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
650 AM CDT Thu Jun 13 2024

.KEY MESSAGES...

- A prolonged period of unseasonably hot weather will continue
  through next week. Temperatures will range from the middle 80s
  to middle 90s, with the heat really ramping up Sunday into early
  next week as heat indices approach 100.

- Storm chances (50-80%) return late this afternoon into tonight.
  Scattered to numerous severe storms are possible with the
  primary hazards being damaging wind gusts in excess of 75 mph,
  large hail up to baseball size, and heavy rainfall.

&&

.DISCUSSION...
Issued at 346 AM CDT Thu Jun 13 2024

An upper shortwave trough is working into the Northern Plains states
early this morning with a 70-90 kt mid-level jet set to push the
wave into the Great Lakes Region later today. A deepening surface
low is working across Ontario/Quebec with a cold front stretched
southward from northern Michigan southwestward into South Dakota as
of 3 am. Decaying convection tied to the front is ongoing over
central Wisconsin and eastern Iowa, and will continue to drop south
this morning, bringing a small chance for a few isolated showers or
a rumble of thunder west of the Illinois River around sunrise.

The cold front will continue to sink south today, approaching the
area late this afternoon and becoming the focus for thunderstorm
development by late this afternoon or early evening. Strong heating
ahead of the front will send temperatures into the upper 80s to low
90s with gulf originated moisture bringing dewpoints into the upper
60s to low 70s. Moderate to strong MLCAPE will develop by this
afternoon with values up to 2500-3000 J/kg. Some capping is noted on
forecast soundings, but will quickly erode as lapse rates steepen
just ahead of the front. Although the mid-level jet will be
displaced somewhat to our north, deep layer shear of 40-45 kts will
be more that sufficient to sustain storm organization. CAMS have
storms initiating over eastern Iowa/northern Illinois by 2-3 pm,
with activity approaching our northern counties sometime between 4-6
pm as it begins to congeal into more of a line segment.
Environmental conditions will be favorable for severe storms with an
enhanced risk (level 3 of 5) for numerous severe storms roughly near
and west of I-55.

Primary hazards with severe storms will be damaging winds
potentially in excess of 75 mph and very large hail up to baseball
size. The threat for tornadoes today is low, but nonzero and would
be tied to any embedded supercells toward the beginning of the event
in the enhanced risk area. Storms should start to lose steam around
midnight as instability wanes, largely putting an end to the severe
threat. A 25-30 kt LLJ nosing into central IL will likely continue
to feed moisture into thunderstorms well into the early morning
hours of Friday until the front pushes activity out a few hours
prior to sunrise. Heavy rain is also a concern as forecast PWATs are
expected to exceed 2 inches, suggesting storms could drop a lot of
rain in a little amount of time. Antecedent dry conditions and high
flash flood guidance should keep the flooding threat marginal, but
if rainfall rates exceed flash flood guidance some issues could crop
up.

Drier air will filter in behind the front to close out the week as
northwest flow becomes situated aloft. Although lower dewpoints will
be seen, air temperatures will still be unseasonably warm both
Friday and Saturday with values topping out in the middle to upper
80s. Hot and humid conditions ramp up once again by the second half
of the weekend as an upper ridge builds east of here putting us
under southwest flow. High temperatures Sunday through much of next
week will be in the upper 80s to middle 90s, with heat indices in
the upper 90s to near 100. An extended period of heat indices at
these values could pose a threat for heat-related illness. The heat
won`t be exiting anytime soon either as the Climate Predicition
Center highlights at least a 60% chance or higher for above average
temperatures through the remainder of the month.

Precipitation chances going into next week will be tied to any upper
waves lifting through southwest flow aloft. A more potent shortwave
will spread through the Midwest states Sunday into Sunday night,
possibly bringing our next chance for showers and storms.

NMA

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 648 AM CDT Thu Jun 13 2024

There is a small chance for a stray shower or storm west of the
Illinois River this morning. Southwest winds become breezy later
this morning with occasional gusts to 20 kts through the afternoon.
A cold front will work through the area tonight, bringing a 60-80%
chance for showers and thunderstorms. Confidence is high that
thunderstorms will occur at or near all terminals, but timing is
still a little uncertain. Because of this, a rather broad window
for storms is mentioned with PROB30 groups for worsened conditions
between 00-06Z. Winds shift to the north behind the front with
speeds below 10 kts overnight.

NMA

&&

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

$$