817
FXUS63 KILX 241714
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1214 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

- Hot weather will briefly return on Tuesday when afternoon heat
  index readings exceed 100 degrees.

- Thunderstorm chances come back into the picture on Tuesday as
  well...with the latest guidance suggesting a Slight Risk
  (15-30% chance) for severe weather along and north of the I-72
  corridor.

- Cooler conditions are on tap Wednesday through Sunday as
  temperatures return to more seasonable values in the 80s.

&&

.UPDATE...
Issued at 1021 AM CDT Mon Jun 24 2024

Surface high pressure centered over eastern IL/western IN will get
shunted further east today as an upper wave sends a cold front
through the Midwest states early this week. Temperatures are on
track to return back into the upper 80s to low 90s today as
dewpoints steadily climb. Heat indices will be similar to air
temperature readings this afternoon, but will jump back into the low
to mid 100s by Tuesday as highs approach the middle 90s with
dewpoints in the low 70s. A couple rounds of showers and storms will
be seen at times through midweek with the highest probabilities
being on Tuesday as the front nears. There is some uncertainty on
how convection may pan out Tuesday morning with a leftover MCS
possibly working through the area. Precipitation chances become
more likely by later Tuesday afternoon/night when the LLJ
interacts with a remnant outflow boundary. 12Z guidance is
starting to trickle in and should provide some clarity on
evolution of convective activity, especially on Tuesday morning.

NMA

&&

.SHORT TERM...(Today through Tuesday)
Issued at 350 AM CDT Mon Jun 24 2024

A warm front currently extending from the western Dakotas to the
Ozarks is serving as the focus for scattered convection across
western Iowa/northwestern Missouri early this morning. This
activity is gradually shifting to the S/SE, but will dissipate
after sunrise as the nocturnal LLJ weakens. While CAMs show the
precip remaining west of the KILX CWA, will need to keep an eye on
the far western counties later this morning as an isolated shower
is not completely out of the question. The warm front will lift
N/NE through the area today...allowing winds to gradually veer
from southeasterly to southerly as the day progresses. This will
help gradually bring slightly warmer/more humid air back into
central Illinois. Resulting afternoon high temperatures will
climb into the upper 80s to around 90 degrees.

A vigorous short-wave trough evident on 08z/3am water vapor
imagery over Saskatchewan/Montana will track eastward today,
interacting with the advancing warm front to trigger several
clusters of thunderstorms across Minnesota/northern Iowa later
this afternoon. These storms will track E/SE across Wisconsin and
Michigan overnight into Tuesday morning. While a few models show
storms potentially spreading/developing as far south as the far
NE CWA late tonight, the bulk of the significant convection will
remain well to the north. Have included low chance PoPs (20-30%)
along/north of the I-74 corridor well after midnight, but think
most of the area will remain dry.

Once the Wisconsin/Michigan storm cluster passes to the N/NE, an
accompanying outflow boundary will sink southward into Illinois
Tuesday morning. Exactly how far south the boundary drops before
becoming stationary is still in question: however, it is becoming
increasingly likely that this boundary will serve as the focus for
scattered thunderstorm development. Based on initial thoughts on
boundary location, have included high chance PoPs (40-50%) along/north
of a Macomb to Bloomington line on Tuesday. The environment to
the south of the outflow boundary will become strongly unstable
with HREF ensemble mean SBCAPEs of 2500-3500J/kg, but weakly
sheared with 0-6km bulk shear of only around 20kt. Any storms that
develop will have plenty of fuel to tap into, but not much shear
for organization this far south. Think the main risk with storms
along/south of the outflow during the day Tuesday will be
scattered large hail/damaging wind gusts due to vigorous updrafts
and sufficient dry air below cloud level.

A cold front will drop southward into central Illinois Tuesday
night, bringing another round of thunderstorms. The exact areal
coverage and severe potential is still somewhat uncertain and will
be highly dependent upon convective evolution earlier in the day.
Stay tuned for later forecasts for more details.

Barnes

.LONG TERM...(Wednesday through Sunday)
Issued at 350 AM CDT Mon Jun 24 2024

The cold front will settle southward into the Ohio River Valley on
Wednesday, allowing a cooler/drier airmass to filter into central
Illinois. With zonal to weakly NW flow expected through the
remainder of the extended, high temperatures will remain in the
80s Wednesday through Sunday. In addition, a second cold front
will bring another chance of much-needed rainfall Friday night
into Saturday.

Barnes

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1213 PM CDT Mon Jun 24 2024

Low pressure will track east across the Upper Midwest and Great
Lakes through tomorrow with a trailing cold front sagging towards
central Illinois Tuesday morning. Ahead of the low, south winds
and VFR conditions are expected to prevail across central Illinois
the rest of today and tonight. There remains uncertainty on
placement and timing of showers and storms associated with the
cold front Tuesday morning, but several models bring precip as far
south as the central Illinois terminals and have included a
prob30 in the forecast to account for this possibility of storms.
Southwest winds will begin gusting to around 20 kt starting mid to
late Tuesday morning. Additional storms are likely later in the
day Tuesday beyond the current forecast period.

Deubelbeiss

&&

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

$$