878
FXUS63 KLOT 100533
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1233 AM CDT Mon Jun 10 2024

.KEY MESSAGES...

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

- 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 /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.

&&

$$

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