THE COOLING TREND CONTINUES—and temps have moved into a BELOW NORMAL phase which is to hold each of the coming 9 days.  


In fact, the season’s first LAKE EFFECT RAIN SHOWERS are possible overnight into Friday morning as “NNE” winds runs southward the length of Lake Michigan give them plenty of time to entrain lake moisture.

Lake effect precip occurs when you have the full fetch winds I just mentioned—but ALSO when cool air sweeps over COMPARATIVELY WARM lake waters—precisely the set up taking shape tonight.  Water temps average out to 73-deg while temps later tonight will have dropped to 46 degrees just a mile above. That steep vertical drop in temps—what meteorologists refer to as a “steep adiabatic lapse rate”—encourages lake warmed air to become buoyant and to rise, cooling as it does. This sets the stage for cloud—and ultimately scattered shower development.  Later in the season, when temps grow cold, this is the type of meteorological set-up which leads to lake effect snow.  THANKFULLY, IT’S NOT COLD ENOUGH FOR THAT TO HAPPEN. We’ll settle for a bit of rain instead.

Whereas this week, which began with 94-deg highs and ends Friday with an early October level 69-deg high—a reading 25-deg cooler—is to average around 74-deg, a reading nearly 4 -deg above normal, the cool air is to tighten its grip and next week will average 9-deg cooler.

In the Atlantic, a monster hurricane is developing—and developing rapidly. Hurricane Lee is headed for potential CAT5 intensity as it tracks across open Atlantic waters avoiding land—but developing HUGE SWELLS which will be crashing on Eastern Seaboard beaches this weekend and into next week. That plus life-threating rip currents will make this a treacherous weekend to be swimming or boating along the East Coast.

While official National Hurricane Center predictions of wind speeds put sustained winds at 160 mph later tomorrow—there are some models that have top wind speeds possibly approaching 190 mph. 

Hurricane have broad impacts on the larger atmosphere.  Because of the shear volume of air they vent out their tops, the subsidence of air at their perimenter can contribute to slowing weather system progression upstream and downstream of these systems. The fact cooler than normal air is to stick around through next week here may be by-product of the hurricanes impact on the larger atmosphere.

One note—some models have Lee traveling northward through the western Atlantic very close to New England later next week. These same models suggest the storm could slam into the Canadian Maritimes.  That’s a long way off and much can happen to this type of storm in interim—but it certainly suggests folks on the East coast have plenty to keep up with in the coming week.



TONIGHT: Frequently cloudy, breezy and cooler. Some lake effect rain showers possible at the south end of Lake Michigan, including the northwest Indiana and extreme northeast Illinois lakeshore areas.  Low 63 in the city—but mid 50s inland.

FRIDAY: Opens cloudy, breezy and cool with some lake effect rain showers possible over and near the south end of the lake. Breaks in the overcast permit mixed sun at times—especially later in the day and Friday evening.  High 69—an early October level temp.

FRIDAY NIGHT: Clearing except for lingering cloud patches near Lake Michigan.  Cool for the season.  Low 59—but low 50s inland.

SATURDAY and SUNDAY: Generous sunshine mixed with some fair weather clouds at times. Cool. High Saturday 73; Sunday’s high 72—60s along Lake Michigan.

MONDAY: Turning cloudy, remaining cool. Growing prospects for showers. High 72.

TUESDAY: Showery, breezy and cool. High 69.

WEDNESDAY: Partly sunny, cool. High 67.

THURSDAY: Mostly sunny, comparably cool temps. High 71.