-- Discussion containing changed information from previous version are highlighted. --
742
FXUS63 KLOT 100800
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
300 AM CDT Mon Jun 10 2024

.KEY MESSAGES...

-- Changed Discussion --
- Dangerous swimming conditions will continue at Lake Michigan
  beaches today.

- Periodic thunderstorm chances exist late Tuesday through
  Thursday night (20-50%). Some could be strong to severe on
  Thursday along with the potential for heavy rain/flooding.

- After a brief break toward the end of this week, summer-like
  heat and humidity returns early next week.
-- End Changed Discussion --

&&

.DISCUSSION...
-- Changed Discussion --
Issued at 300 AM CDT Mon Jun 10 2024

Through Tuesday:

As cooler air spreads into the area early this morning, there
will be a chance of drizzle near Lake Michigan as low clouds
move in from the lake. This chance will end before daybreak.
Clouds will clear from north to south this morning, though some
clouds may linger longer near the lake this morning. Much cooler
high temps are expected today, only reaching the 60s near the
lake to the lower 70s well inland.

Northerly winds will continue today which will allow for high
waves and dangerous swimming conditions at Lake Michigan
beaches. High pressure will build across the area later tonight
into Tuesday morning allowing winds to become light and
variable. Waves will take time to subside but current end time
for the beach hazard statement of 06z looks on track.

The light winds, clear skies and dry airmass will allow low
temps to drop in the upper 40s for most locations late tonight.
Its possible for mid 40s in the usual cool spots. Highs will
rebound back into the mid/upper 70s Tuesday with increasing
clouds in the afternoon as a weak trough of low pressure
approaches the region. cms


Tuesday Night through Sunday:

The upper level pattern will continue to feature generally
zonal flow across the northern Plains placing the Upper Midwest
within a summer-like northwest flow pattern. This typically
comes with increasing heat and humidity across the region, often
accompanied by potential MCSs, which then result in moderating
of that heat and humidity. As is often the case, confidence in
the details remains low at this range.

Beginning Tuesday evening a shortwave is progged to move within
the upper flow with an associated weak surface low moving
across northern Ontario expected to swing a trailing cold front
across the area. This could result in isolated to widely
scattered showers and storms development across northern
Illinois, particularly north of I-80. For now have maintained
15-20% chances for this period.

By Wednesday there continues to be a signal for a possible MCS
somewhere in the region, the location of which remains low
confidence. While the GFS has been quite consistent in something
persisting into portions of far northern Illinois, other
guidance suggests it may be in more of a decaying phase upon
approach. Nevertheless, have nudged up shower/storm chances for
late Wednesday night (after midnight) to 25-30% north of a
Rockford to Chicago line.

Ensemble guidance has been fairly consistent in thunderstorm
development across the area on Thursday. Depending on what
transpires with the late Wednesday, a more robust early morning
MCS could place the better potential south of I-80 where
temperatures in the lower 90s remain likely, whereas a weaker or
even dry overnight period could shift the region of warmer
temperatures and higher instability far enough north to
encompass our entire area. Have opted to cap precip chances at
50% for now due to lingering uncertainties, greatest along/south
of I-88. With the strong upper jet in place there will be
sufficient shear in place to support strong to potentially
severe storms. High PWATs in place would also support a
localized flash flooding threat. Be sure to monitor the forecast
over the coming days!

If we do in fact see robust thunderstorm development Thursday,
the end of the week could end up closer to seasonable, with
highs in the lower 80s (70s near the lake).

Long-range ensemble guidance continues to support a return to
hot and humid conditions across the region early next week as
upper ridging becomes more established across the eastern half
of the CONUS. This will come with increasing potential for heat
related illness as well as continued periodic thunderstorm
chances. Stay tuned!

Petr
-- End Changed Discussion --

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1233 AM CDT Mon Jun 10 2024

Key Messages:

- MVFR CIGS overnight with potential for brief period of -DZ
  and associated MVFR VSBYS and IFR CIGS at ORD/MDW/GYY

1500-2000ft MVFR stratus has overspread ORD and MDW already
this hour and may get close to DPA. Further upstream near
Milwaukee, drizzle has been observed with IFR ceilings near
900ft with visibility also dropping to the 2-4 SM range. To
account for this potential, trended down the inherited TEMPO
groups to include -DZ and 5SM visibility reductions in addition
to IFR ceilings during the roughly 7-11Z timeframe. Confidence
in this maintaining itself into Illinois is not especially high
but felt it was prudent to mention the potential in the TAFs.
Will continue to monitor over the next few hours.

Winds will remain steady out of the northeast across the Chicago
area terminals overnight and generally northerly toward RFD.
Directions could return to a prevailing northerly direction
after daybreak for all terminals but it may vary between
340-020 at times before returning to a prevailing northeast to
easterly direction with an eventual lake breeze passage early
afternoon. Winds become light and variable after sunset.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through late tonight for ILZ006-ILZ103-
     ILZ104.

IN...Beach Hazards Statement through late tonight for INZ001-INZ002.

LM...Small Craft Advisory until 9 PM CDT this evening for the IL
     and IN nearshore waters.

&&

$$

Visit us at weather.gov/chicago