573
FXUS63 KILX 121037
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
537 AM CDT Wed Jun 12 2024

.KEY MESSAGES...

- Unseasonably warm temperatures arrive today.

- A prolonged period of hot and humid conditions begins Thursday
  and continues into next week. Air temperatures will range from
  the upper 80s to middle 90s with heat indices approaching 100
  Sunday onward, posing a threat for heat-related illnesses.

- Shower and storm chances (30-50%) return late Thursday afternoon
  into evening. Some of these storms could become severe with
  damaging winds and large hail.

&&

.DISCUSSION...
Issued at 332 AM CDT Wed Jun 12 2024

Water vapor imagery early this morning shows an upper trough working
through Ontario Canada with a surface trough extending south from
there into the Great Lakes Region. Mid-level moisture tied to this
feature and another upper wave over the southern Plains has allowed
some mid-level clouds to pass through the area overnight. Gentle
southerly flow on the western fringes of surface ridging has been
advecting milder air northward with 3 am temperatures ranging from
the upper 60s across our west to upper 50s in the east where lower
dewpoints are.

Upper ridging over the southwest US will build eastward today,
allowing mid to upper heights to rise throughout the day and putting
a start to a prolonged period of heat. A potent upper shortwave will
dive toward the northern Plains states late tonight, then track
across the northern Great Lakes Region on Thursday. A cold front
will extend southward from its associated surface low and approach
from the northwest going into Thursday night. Thunderstorms will
develop from the Dakotas into western Wisconsin late tonight with
the remnants of that activity entering northern Illinois early
Thursday morning. Most CAMs have this fading out prior to reaching
us, but can`t rule out a stray shower or storm around or just before
sunrise Thursday.

Things turn hot and humid by Thursday as WAA ramps up and dewpoints
approach the middle to upper 60s. High temperatures will approach or
exceed 90 degrees with heat indices nearing 100 in spots (mainly
west of I-55 where the highest dewpoints will be). Most guidance has
instability reaching moderately strong values (~3000 J/kg MLCAPE) by
Thursday afternoon with about 100-200 J/kg of CIN. Upper jet support
will be somewhat displaced to our north, though deep layer shear
of 40-45 kts will be more than enough to sustain any storms that
become organized. CAMs show storms developing over eastern
Iowa/northern Illinois late Thursday afternoon, then dropping
south into central Illinois by early evening as the CAP erodes.
Some of these storms could become strong to severe, posing a
threat for damaging winds and large hail. Climatologically high
PWATs around 2 inches would suggest any storms that develop will
be efficient rainfall producers, though there is only a marginal
threat for flooding due to antecedent dry conditions and the
overall fast progression of the front. The threat for severe
storms should lessen around or shortly after midnight as
instability rapidly wanes.

Somewhat drier air filters in behind the front as flow aloft becomes
northwesterly. This will result in a brief "break" from the humidity
on both Friday and Saturday before an amplified western US ridge
shifts east, turning flow southwest aloft. Air temperatures on
Friday and Saturday will peak in the middle to upper 80s with values
bouncing right back into the 90s by Sunday. Dewpoints will climb
into the upper 60s from Sunday onward, sending heat indices into the
upper 90s to near 100 through much of next week. The threat for heat-
related illnesses will be elevated during this time, especially due
to the duration of the heat and limited relief at night.

NMA

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 537 AM CDT Wed Jun 12 2024

VFR conditions are expected through the TAF period. Diurnal cumulus
will develop by early this afternoon with bases between 6-8k ft.
Winds will be out of the south-southwest with speeds between 8-12
kt.

NMA

&&

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

$$