688
FXUS63 KLOT 081749
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1249 PM CDT Mon Jun 8 2026

.KEY MESSAGES...

- Waves of showers and storms will move through the area today
  with torrential downpours and localized flash flooding.

- Tonight will be damp with low clouds and areas of 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.

&&

.UPDATE...
Issued at 1124 AM CDT Mon Jun 8 2026

This morning, water vapor imagery exposes a mid level shortwave
circulation spinning over the IL/IA/MO tripoint and associated
warm frontal feature lifting north through central IL. This
boundary is pushing a plume of showers and embedded
thunderstorms across northern IL and up into WI. These showers
have been pretty efficient with sites largely reporting 2 to 5
mile visibilities. This is owing to a deeply saturated,
generally warm profile with PWATS of nearly 2" making it easy to
stir up heavier rainfall amid the modest forcing ahead of the
front. MRMS would suggest between 0.5" and 1" fell already this
morning across western and southwestern portions of the CWA, but
now those areas are getting a break while the rain works
through the Chicago metro.

The front will continue advancing northward across northern IL
through the afternoon. Conditions have been quiet behind the
front most of this morning, but just recently are we seeing
pockets of convection go up over central IL and tracking north.
Expectations are for coverage to continue expanding upstream
over the next few hours before pushing up through the CWA during
the afternoon. Further low level moist advection will take
place in the wake of the front and mid-70s dewpoints currently
in central IL will bleed north pushing PWATs up this way past
the 2" mark, which falls in the upper echelon of ILX RAOB
climatology for this time of year. There is some disagreement on
how much we`ll destabilize behind the front this afternoon, but
most camps paint a widespread 1,500 to 2,000 Joules of MUCAPE.
It`s definitely worth mentioning though that CAPE profiles on
forecast soundings are of the tall, skinny variety with
instability well distributed throughout the profile which is
generally more supportive of heavy rain vs severe hazards, and
today will be no exception. Deep layer shear is very weak and
should make it difficult for storms to organize all that well,
but could support water-loaded updrafts and should only enhance
the soaking rain potential.

Our biggest concern with convection this afternoon is
torrential downpours and localized flash flooding. Wet
downbursts will also be possible and a few marginally damaging
wind gusts are not out of the question. Have decided to withhold
a Flood Watch for now given the somewhat progressive nature of
storms later and some uncertainty in coverage, but will keep it
under consideration as we watch upstream activity evolve.
Forcing and instability for heavier rain and thunderstorms will
wane into the evening as the low center moves across, but the
low levels will remain plenty saturated to offer chances for
generally lighter showers or drizzle overnight into early
tomorrow.

This is all to say that the going forecast is very much on
track. Refer to the full discussion below for any details on
later in the week.

Doom

&&

.DISCUSSION...
Issued at 320 AM CDT Mon Jun 8 2026

Today and Tonight:

An early-morning surface map revealed a surface low pressure
system in the northern Plains with an associated double-barreled
warm frontal structure extending eastward across the Lower
Great Lakes. Meanwhile, recent regional water vapor and radar
imagery depict bands of showers and thunderstorms across the
middle Mississippi River Valley associated with a northeastward-
moving upper-level low. Gradually increasing low-level
isentropic ascent atop the broad frontal boundary ahead of the
upper-level low is already supporting scattered thunderstorms
across our area at press time, which is foreboding of what looks
to be a rather wet and humid day.

After daybreak, the double-barreled warm front will merge and
lift northward into the central Great Lakes as the upper-level
low approaches. Coverage of showers and storms should increase
markedly by late morning across central Illinois and spread into
our area during the afternoon hours as the center of the upper-
level low moves nearly directly overhead. Peak coverage in our
local area will be during the late morning through evening
hours (roughly 11 AM to 10 PM), including during the evening
commute.

With forecast soundings by early afternoon and evening
depicting mid-level lapse rates of 5.9 K/km, freezing levels
over 15kft, and PWATs near 2 inches, rain rates today will be
tropical-like and over 2 inches per hour. As a result, any
persistent or redeveloping thunderstorm over the same area may
lead to localized flash flooding, especially if overlapping
where rain has fallen in the past few days or with the urbanized
Rockford and Chicago metropolitan areas. Did give
consideration to issuing a Flood Watch south of I-80 where
pockets of 2-4" of rain fell in the past few days and over the
normally vulnerable Chicago and Rockford metropolitan areas.
However, felt it would be better for the day shift to assess
emerging trends in the densest coverage of downpours today to
inform watch decisions. Finally, cannot rule out a few funnel
clouds today owing to modest veering in the low-level wind
profile and ambient vorticity within the upper-level low (which
may lead to slow-moving low-topped supercell structure as was
the case closer to Davenport, Iowa yesterday).

The upper-level wave will gradually dampen while lifting
northeast toward Lower Michigan this evening, leading to a
gradual decrease in the coverage and intensity of showers in the
area. With that said, the passage of a weak surface low
reflection and the ambient moist conditions should support
expanding drizzle and low clouds across the area. So, while
rainfall intensity should decrease after dark, it`ll still be a
wet night.


Tuesday and Tuesday night:

Owing to a weak low-level pressure gradient, trapped low-level
moisture, and gradually rising mid-level heights, Tuesday may
start rather dreary with cloudy skies and residual pockets of
drizzle. Expansive upper-level troughing across the western
United States will then set the stage for southwesterly low-
level warm air advection into the Lower Great Lakes, leading to
rising surface temperatures. Mean EPS and GEFS height and 850mb
temperature fields support afternoon highs in the mid to upper
80s across the area (assuming clouds do clear as expected). With
dew points still in the lower 70s, it will feel more like the
low to mid 90s. A lack of robust low-level forcing mechanisms
and somewhat muted mid-level lapse rates support daylight hours
of Tuesday being dry.

Tuesday night, continued southwesterly low- to mid-level flow
will advect an EML plume originating in the southern and central
Plains northeastward toward the Great Lakes. Being on the
northeastern edge of am EML plume can be quite precarious as any
subtle perturbation or shortwave moving into the region can
lead to the development of severe thunderstorms rooted to the
nose of associated local enhancements of the low-level jet. With
a growing signal for one such wave to move through the region
during the nighttime hours (ECMWF/EPS in particular are quite
bullish), have cautiously increased PoPs to the middle chance
(30 to 50%) range through the nighttime hours. Have also
touched base with SPC to see if a northeastward expansion and
increase in severe probabilities will be needed in our area for
the Day 2 outlook pending the 12Z suite of guidance.


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.

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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