Wow! A nearly picture perfect weekend summer weekend for Chicagoland.
It's about time in a summer that will likely end up being remembered for the only three conditions we seemed to bounce between: sweltering heat & humidity, smoke but comfy temps, and everyone least favorite- flooding rains.
We can thank a big pattern shift over North America for the more comfortable weather for us- but it's bringing intense heat to the Pacific Northwest and western Canada at the same time. We're seeing what's called a "positive PNA pattern", which describes the jet stream pattern from the Pacific Ocean across North America. In case you were curious, the P is for Pacific, the NA is for North America.
When it's "positive" it's warm/hot in the west and it forces the jet stream to take a dip in the east- providing cooler than average temperatures.
While this looks to hold through this week and into the Labor Day weekend- but I still think "summer weather" is far from over. This pattern only looks to hold until about mid-week next week. I think the signs for heat to return by the second week in September are growing larger when we see a "negative PNA" pattern trying to take hold.
Yesterday we racked up yet another warm day above 80 degrees. It brings our count of days above 80 degrees to 70 days plus at both airports. Last year we saw more than 100 of those warm days- when about 80 is average.
And we're seeing our break from the 90s continue. So far, we've seen more than our fair share of 90s this summer-though not quite record setting. An average August sees about 4 (ORD) or 5 (MDW) days of 90 or warmer. Our current count is 5 at O'Hare and no more are expected before the end of the month.
We've had many days of rainfall this month- all in the last two weeks. But the precipitation this time of year can be both intense and also very spotty. Many times, when we see rain this time of year, the air is juiced enough with moisture (often from the mature corn crop) that we can see these flooding rains develop rapidly on summer afternoons without much warning.
A thunderstorm can develop withing an hour and tap into that moisture for a huge downpour in one locale and then dissipate. And we're seeing the result of a soggy August- so far, it's the wettest start to August in 35 years. One the good-ish side, it's really made a huge dent in our lack of soil moisture.
The USDA's Drought Monitor product that's released on Thursdays shows we're no longer in a drought for now- just pockets of "abnormally dry". August historically is considered our second wettest month of the year. It's only surpassed by May with 4.49'' of rain.
Water temps in the Great Lakes reached peak heat along the Chicago shore earlier this month when the Chicago lakefront hit 77 degrees. That's one degree warmer than all of last year. That will have a big impact on our fall weather.
Water hangs onto heat much more effectively than air does- so the lake will stay warm even when the air starts to get cold in late fall. That combination can make for some big lake effect snow later this year- and in the fall, it can bring lake effect showers in rain form too.
Things to mark on your calendar ahead in the coming weeks: our last sunset of the year at 7:30p or later happens on Friday the 29th. The Full Harvest Moon will grace our skies on the 6th and 7th of September. The Harvest Moon rises just as the sun sets since we're so close to the fall equinox. We'll have sunsets after 7p until September 16th. The Autumnal Equinox is on September 22nd this year. The new season officially starting at 1:19p in our time zone according to our friends at the Adler Planetarium. Around the equinoxes the sun rises and sets due east and west -- so from the 21st to the 23rd you can get those great "Chicagohenge" photos. And it's only 67 days until our first average snowfall occurs- so enjoy these pleasant summer days while you can.