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| Satellite view from late Sunday afternoon. Clouds from former Tropical Storm Ophelia reach about as far as Route 2 in Vermont. Wisps of wildfire smoke are visible in the clear air over far northern Vermont. Much more smoke is visible in Quebec and that will contribute to haze much of this week. |
We call these spells Indian Summer, and we're entering such a spell now. Technically, Indian Summer strikes after a good autumn frost. We haven't had one yet, but overall, the weather will fit.
In the past, especially way back in the mid 20th century, the sunshine with these Indian Summer spells mixed with quite a bit of haze. That's because these huge high pressure systems featured temperature inversions.
Inversions are a warm layer in the atmosphere atop a cooler layer near the surface. The inversion acted like a lid, trapping pollutants.
The dense morning fog that is characteristic of weather pattern would sometimes become mixed with the pollutants to become smog, and that smog in some of the most industrial places in the U.S. (think Pennsylvania steel country) would never lift.
In the worst cases, this would get deadly. The most famous case was in Donora, Pennsylvania in October, 1948, when a thick smog choked the town for five days, killing at least 20 people and sickening at least half the town.
This incident was the spark for the Clean Air Act and other anti-pollution initiatives.
Decades later, spells of Indian Summer weather across the Northeast were much less hazy as a result. There was less pollution in the air to trap, so skies remained deep blue, the air remained easy to breathe.
Now, though, it appears the haze is back. A very typical for the season big high pressure system is now stalled in Quebec, and beginning to nose more and more into New England. The sky under much of this high, though is not a brilliant blue. Instead, wildfire smoke, which has plagued Canada much of this year, is trapped in this big area of calm, fair conditions.
So, we're going to have a week of gorgeous autumn weather - Indian Summer if you will - here in Vermont, expect hazy skies during much or even all of this long stretch of mild, pleasant weather this week.
Unlike Donora in 1948, a lot of this smoke and haze is aloft, and not much is near the surface. That means, thank goodness, the air won't be all that unhealthy to breathe. Most of the tiny particles in the haze that can damage lungs is high overhead.
I noticed air quality in Vermont Sunday and this morning was in the moderate category. That means it's not exactly fresh and clean out there, but for the vast majority of us, pollutants aren't at any kind of dangerous level.
Although I admit the following is speculation, I think the haze associated with Indian Summer is back to stay. Summer and early autumn wildfires in Canada and the western United States will generally be more common and widespread than in the past, due to climate change.
The smoke will swirl into these big high pressure systems that bring us Indian Summer, and we'll be back to the autumn haze of mid-20th century America.
Bottom line for us is the clouds and sprinkles that came north from then-Tropical Storm Ophelia over the weekend are slowly eroding and heading out of Vermont.
It's going to be a full week of mild afternoons with plenty of sun (with some smoke and haze). Highs will be in the 60s and low 70s daily all week, which is a little warmer than normal. Each morning will feature patchy dense fog, especially in river valleys. Lows will be mostly in the 40s, about average for this time of year.
We haven't had a stretch of dry weather as long as this since late May and early June.
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