262
FXUS63 KLOT 172338
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
638 PM CDT Wed Jul 17 2024

.KEY MESSAGES...

- A generally quiet weather pattern will prevail though the end
  of the week

- Chances for showers and storms will return early next week
  (20-40% chances areawide).

&&

.DISCUSSION...
Issued at 211 PM CDT Wed Jul 17 2024

Through next Wednesday...

Our area remains on the outer fringe of a deep upper-level trough
and associated pool of seasonably cool air propogating across the
Upper Great Lakes region. Tonight, a pair of embedded upper-level
vort maxes (seen readily over Green Bay and Ironwood, Wisconsin
via water vapor satellite imagery) will swing southeastward
over far northeastern Illinois and northwestern Indiana, causing
northerly winds and waves to increase down the spine of Lake
Michigan. With forecast wave heights now expected to exceed 4
feet for 12 to 18 hours from this evening through tomorrow
morning, will go ahead and issue a Beach Hazards Statement for
Lake and Porter counties in northwestern Indiana. Thickening
clouds beneath each shortwave may support a few sprinkles
overnight and tomorrow morning too, particularly in northeastern
Illinois northwestern Indiana.

Tomorrow through Saturday looks decidedly quiet as the surface high
pressure system currently in the Northern Plains slides
southeastward and through the Great Lakes region. Highs in the upper
70s to lower 80s, overnight lows in the mid to upper 50s, and plenty
of sunshine will prevail. Daily lake breezes will keep shoreline
locations cooler each day.

Sunday, ensemble model guidance depicts the development of a
disorganized cut-off low pressure system over the Upper Mississippi
River Valley, which will likely drift eastward through early next
week. As a result, chances for shower and storms will return to the
area with perhaps a modest tie to the diurnal curve (relatively
higher chances, 30-40%, during daylight hours and lower chances, 20-
30%, during nighttime hours). With that said, early next week does
not look like a washout with many dry hours, and perhaps areas,
currently expected.

Looking toward the final week of July, ensemble model guidance is
exhibiting a weak signal for a return of above-average temperatures
and perhaps a more thunderous pattern (especially toward the last
few days of the month).

Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 638 PM CDT Wed Jul 17 2024

The main forecast concern this period is a wind shift to the
northeast early this evening. A lake breeze moved through MDW a
few hours ago and may move back through MDW briefly over the
next hour before the entire boundary shifts west of ORD/MDW
with prevailing northeast winds this evening. Winds may drift
back to northerly or even north/northwest late this evening and
overnight, then turn back to the northeast Thursday morning.

There may be sct, possibly bkn high mvfr or low vfr level clouds
overnight along with a few sprinkles. Confidence is fairly low.
cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Beach Hazards Statement through Thursday morning for INZ001-
     INZ002.

LM...Small Craft Advisory until 10 AM CDT Thursday for the IN
     nearshore waters.

&&

$$

Visit us at weather.gov/chicago