300
FXUS63 KLOT 092327
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
627 PM CDT Sun Jun 9 2024

.KEY MESSAGES...

- A cold front will arrive this evening with gusty northerly
  winds lasting through Monday along with building waves and
  dangerous swimming conditions for Lake Michigan beaches.

- Tuesday through the end of the week will feature increasing
  temperatures and chances for showers and thunderstorms, with
  the latter particularly on Thursday and Friday.

- After a brief respite on Saturday, summer-like temperatures
  are poised to return early next week.

&&

.DISCUSSION...
Issued at 233 PM CDT Sun Jun 9 2024

Through Monday night:

A mid-level trough and associated surface trough/front will
shift S/SSE across the forecast area this evening into the early
overnight hours. A wind shift from WNW to NE with gusts to 20
knots is expected along the Lake Michigan shore early to mid-
evening and will result in deteriorating swimming conditions. A
Beach Hazard Statement remains in effect beginning 9pm this
evening for the entire Lake Michigan shore in IL and IN, with
the potential for dangerous swimming conditions to begin as
early as 8pm if the front exhibits a quicker forward motion over
the next several hours. A secondary wind push late this evening
with gusts of 25 knots or higher will generate continued
dangerous swimming conditions through the day Monday.

A mixed nocturnal PBL owing to modest CAA overnight may allow
the post frontal stratus to grow sufficiently deep to squeeze
out some sprinkles or patches of drizzle. This is particularly
the case near the lake where added lake moisture from a long
fetch will counteract overall synoptic dry air advection. Have
opted to include slight chance sprinkles roughly around the
lake-adjacent counties late this evening through sunrise Monday.

Otherwise, diurnal heating and continued dry advection should
erode the stratus or lift and scatter the stratus into shallow
cumulus from north to south through the morning Monday. Max
temps will be well below normal for early/mid June, with highs
ranging from the low 60s along the shore to the low 70s well
inland. Mostly clear skies and a passing ridge Monday night will
yield a chilly night with lows in the mid to upper 40s inland
to the low 50s in the core of the Chicago metro.

Kluber


Tuesday through Sunday:

Next week, a quintessential summertime ridge is expected to
develop across the west-central United States leading to quasi-
zonal to northwesterly upper-level flow across the Great Lakes.
The result locally will be gradually warming temperatures
Tuesday through the rest of the workweek. Highs on Tuesday in
the upper 70s will warm to the mid to upper 80s by Thursday,
with overnight lows climbing into the low to mid 60s.

Chances for precipitation will be tied to upper-level
shortwaves embedded in the flow aloft. The first wave will swing
through the Great Lakes in the Tuesday night into Wednesday
morning timeframe, though low-level moisture return ahead of the
wave looks rather limited. As a result, only a few scattered
non-soaking showers are our expectation, warranting low-end
(15-20%) PoPs. The next wave (or series of waves) will move
through the general region in the Wednesday night to Friday
timeframes. With plenty of upper-level shear (thanks to the
proximity of the upper-level jet focused to our north) and
moisture-laden instability, the pattern will be supportive of
episodic mesoscale convective systems (MCSs) with gusty to
damaging winds and soaking downpours. Pinpointing the times and
locations of summertime MCSs is a futile effort more than 48
hours out, so for now, will carry mid-range chance (30-40%) PoPs
centered on Thursday in favor of refinements in the coming
days. It`s worth noting temperatures Thursday and Friday will
depend on the cadence of convective episodes, any debris upper-
level cloud cover, and the eventual placement of an effective
(outflow-reinforced) front.

By Saturday, any effective front reinforced by episodic
convective episodes should slip south of our area leading to
onshore flow and a modest break in seasonably warm temperatures.
Highs should range from the lower 70s lakeside to the low to
mid 80s inland. Thereafter, ensemble guidance supports the
development of pronounced troughing across the western US and
ridging over the Great Lakes, which should lead to a return of
summer-like warmth (as well as humidity) at some point early
next week.

Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 625 PM CDT Sun Jun 9 2024

Aviation weather concerns are:

- Incoming NE wind shift with a cold front.
- Potential MVFR cigs tonight and a small chance for a few
  sprinkles

A strong cold front is moving rapidly southward down the lake
and will be delivering a NE shift at ORD, MDW, and GYY shortly,
and a bit later this evening at DPA. Gusts up to 30 knots are
expected near GYY and about 25 knots at ORD/MDW as the front
passes.

Generally VFR cigs are expected tonight although some spotty
MVFR cigs may materialize overnight. A few sprinkles/showers
can`t be ruled out tonight, although chances are too low for a
mention in the outgoing 00z TAFs. Cigs will gradually lift
tomorrow and winds will ease. At ORD/MDW, winds may oscillate
between 350 and 020 through the morning before a lake breeze
reinforces NE winds during the afternoon.

Carlaw

&&

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

IN...Beach Hazards Statement through late Monday night for INZ001-
     INZ002.

LM...Small Craft Advisory until 9 PM CDT Monday for the IL
     nearshore waters.

     Small Craft Advisory until 9 PM CDT Monday for the IN
     nearshore waters.

&&

$$

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