927
FXUS63 KILX 232300
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
600 PM CDT Sun Jun 23 2024

.KEY MESSAGES...

- Hot and very humid conditions return Tuesday with heat index
  values between 100-105 degF, posing a risk for sensitive
  groups.

- Multiple chances for thunderstorms span the middle-to-late portions
  of this week, bringing an attendant risk for severe weather and
  heavy rainfall.

&&

.DISCUSSION...
Issued at 223 PM CDT Sun Jun 23 2024

Large-scale subsidence has settled in behind a departing upper-level
trough and surface cold front.  Cool, calm conditions are
anticipated tonight as high pressure builds directly across central
Illinois.  While patchy fog is often associated with these types of
synoptic patterns following a rain event, there is very little
signal evident in forecast guidance.  Beneath mostly clear skies,
overnight temperatures are likely to crash into the mid 60s; some of
the coolest readings in over a week.

Our welcomed cool-down will quickly yield to a warming trend Monday
and Tuesday.  By then, an upper ridge axis will shift across the
area in response to hot, Gulf air advecting northeastward into the
Mid-Mississippi Valley ahead of a frontal zone.  Temperatures will
warm into the low 90s on Monday, then the low-to-mid 90s on Tuesday.
Of the two hot days, Tuesday will feel more oppressive as a warm
front lifts in and brings with it a surge of humid air.  The current
forecast for heat index values on Tuesday is 100-105 degF. This will
put central Illinois in the conversation for its first Heat Advisory
of the year, but with notable bust potential.

An active weather pattern then returns Tuesday - Wednesday as a
series of shortwaves breaks down the upper ridge and helps force a
surface cold front into central Illinois.  While the synoptic
pattern looks favorable for multiple rounds of thunderstorms during
this period, the timing will remain unknown until the hi-res
guidance (ARW, HRRR, NSSL WRF, etc) begins to better resolve the
upstream mesoscale pattern.  And even then, guidance notoriously
struggles to depict the evolution of MCS/MCV/outflow features. What
we do know at this point, however, is that the ambient environment
is conducive for severe weather and torrential rainfall given
explosive CAPE profiles, just enough shear, and weak Corfidi
magnitudes (better backbuilding-MCS potential). As alluded to
above, any early- day convective debris on Tuesday could play
spoiler to heat headlines.

Cooler and drier conditions will settle into the region later
Wednesday through Thursday as a ridge of high pressure builds across
the region.  Afternoon temperatures in the mid 80s will be most
common, and these will be accompanied by low RH values.

Additional rain chances exist by late week as progressive late June
flow brings yet another cold front into central Illinois.
Temperatures ahead of this front are once again forecast to spike
into the 90s.

MJA

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 600 PM CDT Sun Jun 23 2024

A high pressure ridge currently stretched across IA and MO will
shift east over central IL tonight. This will allow gusty
northwest winds to diminish quickly this evening, then remain calm
to light/variable through sunrise. As the high shifts farther
east, SSE winds will eventually develop on Sunday. Skies to be
mainly clear with scattered high based cumulus or alto-cu Sunday
afternoon.

25

&&

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

$$