A cold front brings chance of showers this weekend



–The month of August and the 3-month METEOROLOGICAL SUMMER SEASON end at midnight tonight. Summer’s been dry and warm overall. August finishes with a modest half degree surplus and half the normal rainfall—-2.05″ versus the normal of 4.11″.  That an O’Hare August rain deficit of 2.06″

–August closes with a second consecutive 100% sunny day. That’s the first time we’ve put back-to-back 100% sunny days together over 3.5 months—since May 12-13, Frank Wachowski tells us.  By the way, Franks tells me the June through August SUMMER SEASON generated 65% of its possible sunshine–which is precisely normal!

–While the Western U.S. broils, the dome of warm air its producing high into the atmosphere there creates a northward buckle in the jet stream over western North America. Those steering winds then slide southeastward out of Canada into the Chicago area. This will tap the warm air to our west into Saturday but spare us the stifling humidities of a direct flow out of the tropics.

–Daytime temps into Saturday will surge into the 80s—with readings very close to 90, especially Friday.

–Saturday will see a cold front drop through the area shifting winds “NE” and potentially generating several showers or thunderstorms–though chances are modest with areal coverage of any rain in the 20 to 30% range as it looks at the moment.

–As anyone who swims or boats in the area has observed, the arrival of “NNE” winds fosters wave development on Lake Michigan. The reason is simple. NNE winds spend more time over water getting here and have more time to transfer their energy to the lake surface in the form of waves. So, we have to monitor the prospect Lake Michigan may grow choppy Saturday into Sunday with rip currents which may impact holiday weekend swimmers. 

–While the NNE weekend winds will lower temps, looking out over the next 2 weeks, only one of the coming 15 days come back at us when temps are averaged across a collection of forecast models with below normal temps. IN other words, 14 of the coming 15 days will finish with temp surpluses each day—a trend reflected in the 6 to 10 and 8-to-14-day TEMP TREND FORECAST from the National Weather Service’s Climate Prediction Center.

–One this to monitor for the holiday weekend. Model guidance maintains fairly elevated dew points here at ground level. This could be a proxy for some clouds–even a few scattered showers popping from time-to-time Sunday and Monday. It’s something to monitor.


TONIGHT: Mainly clear. Comfortable and seasonable temps and humidities. Low 62–with a few mid 50s cooler locations away from the city and lake.

THURSDAY: Sunshine mixed with some afternoon and evening clouds. Modestly above normal early Sept temps as the new month gets underway.  High 87–but mid 70s to around 80 on area beaches.

THURSDAY NIGHT: Partly cloudy, warm. Low 70.

FRIDAY: Mixed sun and clouds, quite warm with modestly higher humidities. Slight chance of an isolated shower or two in the afternoon–but with low coverage, High 88.

SATURDAY: More clouds but with spells of mixed sun. Winds shift northeast off Lake Michigan lowering temps, especially lakeside areas. Several scattered showers, a few possibly thundery–but impacting only 20 or 30% of the area. High 87 inland–but falling back to the upper 60s or low 70s along Lake Michigan.

SUNDAY and MONDAY LABOR DAY: Cloudy spells but mixed sun is not out of the question at times. A few spotty showers can’t be completely ruled out–but with a majority of hours rain-free. High Sunday 76; Monday’s high 80—but upper 60s to mid 70s along Lake Michigan.

TUESDAY and WEDNESDAY: Cloudy spells continue, higher humidities. A shower or two is possible–but only marginally possible. Highs both days 82.

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