364
FXUS63 KLOT 062007
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
307 PM CDT Sat Jun 6 2026

.KEY MESSAGES...

- Isolated to scattered showers and thunderstorms will continue
  through this evening, with the highest thunderstorm coverage
  remaining south of I-80. The strongest storms south of I-80
  may produce strong to damaging winds and hail up to quarter
  size on a localized basis.

- While there will be daily shower and thunderstorm chances
  through the upcoming week, expect plenty of dry hours. Outside
  of the convective chances, it will be very warm and humid
  (focused away from the lake until Tuesday).

&&

.DISCUSSION...
Issued at 307 PM CDT Sat Jun 6 2026

Through Sunday Night:

GOES visible satellite imagery this afternoon shows several
regions of agitated cumulus in and near our forecast area. The
most congested cumulus has generally been focused near the lake
breeze and along a somewhat diffuse remnant outflow boundary
from last night`s convection that has been laid out across our
far southern counties and into central Indiana, but deeper
cumulus growth has also been noted within a couple of low-level
confluence/convergence zones across the northern half of our
forecast area. Synoptic-scale forcing remains fairly nebulous
and pretty much limited to very modest isentropic upglide, but
within moist and unstable summertime air masses like the one in
place today, it typically does not take much for convection to
get going, and that has been the case today. That said, the
relative lack of large-scale ascent has kept convective coverage
isolated to widely scattered thus far, and that should largely
continue to remain the case through this evening.

Across our southern counties, RAP objective mesoanalysis
depicts 2000-2500 J/kg of MLCAPE amidst 15-25 kts or so of deep-
layer shear. This environment was just favorable enough to
yield severe downburst winds and small hail in Benton County, IN
with a tall storm that briefly pulsed up there a little while
ago, and would not be surprised to see another instance or two
of localized damaging winds and hail up to quarter size with any
convective updraft cores that manage to pulse up towards the
~13 km AGL equilibrium levels south of I-80. Farther north, a
more pronounced warm nose at around 600 mb may inhibit
convective growth to a greater degree in the absence of
stronger forcing for ascent, making it less likely for cells to
grow tall enough to produce severe winds and hail there, in
addition to reducing the overall likelihood of lightning.
Lastly, could not entirely rule out a funnel cloud or even a
landspout occurring somewhere as slow-moving cells develop
along surface boundaries in this moist and unstable air mass.
The latest RAP mesoanalysis depicts non-zero non-supercell
tornado parameter values in a few spots, which supports this
thinking.

A slight enhancement to the low-level jet this evening may
allow for disorganized convection to fester across our southern
counties for at least a few hours after sunset, and possibly
well into the night. This convection should eventually diminish
in coverage, though, as the attendant instability reservoir
becomes increasingly depleted with time tonight. The resulting
lull in convective activity should persist through at least
mid-morning tomorrow before large-scale forcing increases
toward midday as a closed-off upper-level low presently located
over the southern Plains lifts northward toward our latitude and
becomes sheared-out as it does so. Despite the weakening nature
of the forcing associated with this disturbance, the persisting
rich low-level moisture (surface dew points up to around 70F)
and diurnal destabilization as surface air temperatures warm
into the 80s will support another episode of convection in our
forecast area into the afternoon hours. This time around,
convective coverage looks to be greatest across the southwestern
half or so of our CWA. Minimal deep-layer shear will also
encourage tomorrow`s convection to have a pulse-like character.
Enough instability will be present to support a gusty wind and
small hail threat with the strongest updrafts that pulse up,
but subpar lapse rates and DCAPE should keep storms sub-severe.

Ogorek


Monday through Friday:

The aforementioned weakening mid-upper low/short-wave will
continue to shear out Sunday night into Monday as it encounters
robust ridging centered over the eastern Lakes by then.
Nonetheless, weakly capped tropics- like airmass should support
fairly widespread showers and at least scattered storms
developing as early as midday Monday (unless debris cloudiness
proves too detrimental to sufficient destabilization).
Southeasterly synoptic flow and lake breeze reinforcement will
keep IL shoreline locations in the 70s on Monday, while the rest
of the area reaches the low- mid 80s.

Looking ahead at the rest of next workweek, there have been some
guidance members with sufficiently strong mid-level ridging and
low-level thermal ridging poking into the Great Lakes region for
a few days of very warm (locally hot) and humid conditions. With
that said, the more likely scenario is our area being on the
precarious northwestern periphery of ridging centered near the
East Coast. This should entail less capping and a continuation
of shower and thunderstorm chances. By later in the week
(Thursday or thereabouts), seasonably strong troughing from the
north central US to central Canada could plausibly yield a
pattern supportive of organized strong to severe convection into
the region.

Note that the NBM depicted temperatures centered Tuesday through
Friday (most notably on Wednesday and Thursday) are well
outside of the ensemble spectrum due to likely spurious upward
bias correction. Thus we will withhold from any heat messaging
locally. It looks to be very warm and humid, but not hazardously
so, per the current global ensemble guidance consensus.

Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1231 PM CDT Sat Jun 6 2026

Key Aviation Messages for the current TAF period:

- A lake breeze arrival this afternoon will shift winds to the
  east-northeast

- Isolated thunderstorms near the lake breeze this afternoon,
  but better chances for thunder to the south of the Chicago
  Metro

Currently, conditions are VFR with light southerly winds.
However, A lake breeze has already started to move inland away
from the lake. Winds will switch to the northeast behind it with
winds 5 to 10 knots.

Isolated showers and storms are expected this afternoon. However,
the better coverage of thunderstorms is expected south of a KSQI
to KVPZ line. That being said, the previously mentioned lake
breeze could be enough forcing to trigger convection that could
develop into at least a shower if not a thunderstorm near the
terminals. While confidence is lower in any one cell directly
passing over a terminal, the PROB30 was converted the -SHRA
mention to the -TSRA given the amount of instability present on
an already warm June afternoon. Chances for showers and thunder
diminish after 23Z. Light northeast winds will slowly become
more easterly tomorrow morning.

DK

&&

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

&&

$$

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