May 25, 2018
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Why This Weather?

Vacationers and Mainers are looking at the sky, asking, rhetorically: Why? As unpredictable as the weather is in northern New England, meteorologist Ken McKinley has some answers to that question.

Mr. McKinley operates a business in Camden called Locus Weather that provides forecasts for radio stations and individualized forecasts for mariners from Maine to the Mediterranean. Mr. McKinley graduated with a degree in atmospheric sciences from Cornell University, then attended Massachusetts Institute of Technology, where he continued studying meteorology.

First of all, Mr. McKinley says, it’s not our imagination. “It’s been wet,” he said, with measurements showing Portland is just three inches shy of a record for the summer. And it’s not just the volume of rain. Instead of a several days of downpours, most of the precipitation has come over a period of weeks of cloudy, rainy days.

So what is to blame?

“It all goes back to the upper-level pattern,” Mr. McKinley said, “what people call the jet stream.” Actually, he explained, the air flow patterns that determine weather occur just below the jet stream. On a continental map, the air flow typically looks like a railroad line in hilly territory. The ridges may extend north to Michigan, and the troughs may dip down to Texas.

This June and July, the map looks like a roller coaster. One trough set up along and just off the East Coast, Mr. McKinley explained, that allowed cool, damp air to slide into our area, bringing low pressure systems off the Atlantic. That’s why June saw “chilly, rainy weather.”

Then, a second pattern was established that featured a ridge over Texas, Oklahoma and Kansas, producing “unending hot weather” there. That ridge blocked air flow across the continent, giving the West Coast cool, wet weather, along with our corner of the country.

In late July, the pattern changed, and the trough that had plagued New England moved to the west, producing southwest winds that drew warmer, moist air from the mid-Atlantic and even the Gulf of Mexico. The Bermuda high, a ridge of air that often gives New England long stretches of sunny and warm days in the summer, had not moved close to the East Coast as it typically does by this time.

Back in the middle of the country, the ridge that gave Kansas hot weather is now over the Pacific Northwest, bringing temperatures of 103 to Seattle and 106 to Portland in recent days.

“These long-wave patterns tend to move slowly,” Mr. McKinley said.

The Bermuda high is now returning to the Atlantic coast, so conditions have improved. Let’s hope it stays.

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