076
FXUS63 KLOT 081942
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
242 PM CDT Mon Jun 8 2026

.KEY MESSAGES...

- Heavy showers and embedded thunderstorms will move through the
  area this afternoon into early evening. Torrential downpours
  will be possible and may lead instances of flash flooding.

- Tonight will be damp with isolated showers and drizzle.

- Tuesday through Thursday will be noticeably warmer and more
  humid with daily heat indices in the 90s.

- Several rounds of severe thunderstorms may occur in the
  general region Tuesday night through Thursday.

- Temperatures will trend cooler Friday onward, along with lower
  humidity.

&&

.DISCUSSION...
Issued at 242 PM CDT Mon Jun 8 2026

Through Tuesday Night:

Early this afternoon, water vapor imagery showcases a midlevel
shortwave perturbation spinning over far eastern IA. A plume of
heavy showers with embedded thunderstorms recently exited the
area to the northeast after leaving behind anywhere from a half
an inch to an inch of rain around parts of the CWA this morning.
The heavy rain rates and lowered visibilities were made
possible by a deeply saturated, generally warm profile with
PWATS of nearly 2". The forcing was provided by a northward
progressing warm front which has now lifted into southern WI. In
the wake of this front, we`ve seen a hiatus in precip coverage
although dewpoints continue to climb, now largely getting into
the middle 70s pushing PWATs above that 2" mark. Additional
storms are now entering the CWA from the southwest as of around
2 PM, driven by a vort lobe/secondary warm frontal feature
lifting through IL extending east from the low center. Heavy
rain rates have been observed across central IL recently, a
couple as high as three to four inches per hour.

This plume will continue advancing northward through northern
IL and northwest IN through the afternoon, and we expect the
heavy rain rates to continue as it does with torrential
downpours and flash flooding our biggest concerns with this
afternoon activity. Forecast soundings for this afternoon are
very reminiscent of a tropical environment exhibiting very weak
deep layer shear and 1,500 to 2,000 Joules of tall, skinny CAPE.
The weak shear should make it difficult for storms to organize
all that well and greatly limits the overall severe potential,
but is supportive of water-loaded updrafts and furthers concerns
for localized flooding. These concerns prompted us to issue a
Hydrologic Outlook our IL counties to highlight the flash flood
potential. With impacts looking more likely on a localized basis
vs more widespread, opted to hold off on issuing a Flood Watch,
but near-term trends will continue to be monitored closely for
any reconsideration. Wet downdrafts will also be possible and
strong, likely non-damaging wind gusts are on the table.
Finally, strong low level vorticity extending from the low and
some low level shear could lead to the development of some
funnel clouds, particularly in our south and west. An SPS was
recently issued for these areas for the possibility of funnel
clouds.

This main plume and the flood concerns should push out of the
CWA during the early evening as the vort lobe does. The low
center will scoot from far NW IL across southern WI tonight into
tomorrow. Forcing and instability will wane after dusk, but
plenty of low-mid level moisture and transient forcing will be
present to keep chances for isolated to widely scattered showers
going through the night.

With the sheared out low still working across the region,
lighter rain or drizzle could remain into Tuesday morning with
mostly cloudy skies likely to start the day. A warmer air mass
out over the Plains will be allowed to translate east into the
Midwest behind this current wave. Afternoon highs are forecast
to push into the middle and upper 80s, including up to the
lakefront. Dewpoints still hanging out in the lower 70s will
result afternoon heat indices into the lower 90s. We`ll
destabilize nicely during the day, however a big lack of forcing
should inhibit most convection and largely dry conditions are
anticipated.

A storm system developing off the lee of the Rockies today will
mature through tomorrow and is expected to track northeastward
into the middle of the week. As the eastern edge of the upper
trough moves over the region, an EML will spread east into our
region late. Guidance favors an MCS forming well out to our west
during the day on Tuesday and continue into the night on the
nose of the nocturnal LLJ. Most camps steer this system to our
north and leave us largely dry or with only isolated activity
during the night, but some (namely the Euro) bring storms across
our CWA late tomorrow night into early Wednesday as a warm
front may stall in the area. If storms were to occur, damaging
winds and potentially some hail would be the biggest concerns.


Wednesday and Wednesday Night:

Any lingering thunderstorms at daybreak Wednesday should end by
mid-morning as low-level capping increases at the base of the
EML plume and the low-level jet weakens. A largely dry day will
then set the stage for temperatures to warm to the upper 80s to
lower 90s (heat indices in the mid to upper 90s).

Wednesday evening, an upper-level shortwave embedded in the
aggregate troughing will lift into the Upper Mississippi River
Valley leading to the development of severe thunderstorms across
Minnesota and Wisconsin. A separate region of thunderstorm
development may take place in central and eastern Iowa tied to a
secondary, more subtle, 500mb wave. Assuming this occurs,
convection may try to continue eastward across the Mississippi
River and across northern Illinois/northwestern Indiana during
the evening and overnight hours. However, do wonder if
thunderstorms would tend to struggle into northern Illinois
given (1) the upper-level jet and associated region of deep-
layer shear will be displaced northwest of our area and (2) the
terminus of the low-level jet will be focused into Wisconsin.
With that said, any development of a deep cold pool would
sustain a threat for outflow-driven convection well into the
nighttime hours given an expansive reservoir of instability
across the region. In all, will watch the Wednesday night
timeframe for a threat for severe weather in the general region.


Thursday:

The forecast for Thursday carries quite a bit of uncertainty.
In the wake of the lead shortwave responsible for thunderstorms
Wednesday evening, a few individual models are hinting at a
trailing subtle secondary wave moving through the central Plains
during the overnight hours into early Thursday morning. In such
a scenario, initial elevated convection in the
Nebraska/Kansas/Iowa region may evolve into a forward-
propagating MCS that would be encouraged to roll toward northern
Illinois after daybreak. Confidence in this scenario is rather
low.

Assuming there isn`t an MCS rolling into the area during the
morning, Thursday should be another warm and humid day with
highs in the 80s and heat indices remaining in the 90s. A strong
upper-level shortwave and associated cold front is then
expected to swing into the Midwest during the afternoon and
evening hours. This time frame looks to be the most concerning
for an episode of severe weather in our local area with an
overlap of strong low-and deep-layer shear, steep mid-level
lapse rates, and moisture-laden instability profiles. A mix of
supercells and bowing segments certainly seems realistic with a
threat for all hazards.


Friday Onward:

In the wake of the cold front, Friday and Saturday should be
noticeably cooler and less humid. Ensemble mean highs from the
EPS and GEFS range from the upper 70s to lower 80s with
overnight lows in the mid to upper 60s. Am quite confused as to
why NBM guidance putting chances for showers and thunderstorms
in the forecast for our area Friday night into Saturday given a
large surface high pressure system will be moving through the
area in the wake of the cold frontal passage. Ensemble guidance
supports temperatures trending below average (highs in the low
to mid 70s) and a return of rain chances next week as aggregate
troughing develops over the northern United States in some
fashion.

Doom/Borchardt

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1249 PM CDT Mon Jun 8 2026

Main Aviation Concerns:

- Widespread SHRA and TS chances increase through this
  afternoon, lingering into the evening.

- Low ceilings and reduced visby`s will shift into the region
  late afternoon through the overnight.

- Winds will gradually shift from the southeast early this
  afternoon, to the south moving into the overnight, then west-
  southwest Tuesday morning.

A low pressure system is slowly tracking eastward across Iowa,
and expected to continue shifting eastward over the next 24
hours. This will bring widespread SHRA and TS chances to the
terminals throughout this afternoon and evening. Showers
currently over the metro terminals will continue to diminish
over the next hour, however a larger cluster of SHRA and TS
across central IL will continue lifting north-northeast this
afternoon. Converted the previous PROB30 to TEMPO inside the
20-24z time frame to account for a more localized impact window.
Current visby`s and intensity`s were based on current obs in
central Illinois, however, the need for reduced conditions may
be needed with future AMD`s. With any stronger showers and
storms, prevailing east- southeast winds could become variable,
and gust upwards of 20-25kts.

After the main cluster of SHRA and TS lifts north-northeast
early this evening, lingering -SHRA and BR will be possible into
the early night. With passage of the low pressure core
overnight cannot rule out additional -SHRADZ, which was
inherited from previous TAFs. IFR ceilings will prevail with
the weakening winds and abundant moisture at the surface,
however held off on any mention of LIFR...but cannot rule out
the potential across northern IL and far northwest IN. West-
southwest winds prevail Tuesday morning, increasing through the
afternoon with gusts around 18kts.

Baker/DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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