2 days ago
Looks like rain in Boston for the 14th weekend in a row. Is it science or just bad luck?
With rain in the forecast to some extent both days this weekend (though mainly on Saturday), we will set a new record — 14 weekends in a row with measurable rain in Boston. .
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Science vs. unlucky timing
I'll get right to it: our weekend woes are due to both an annoying weather pattern and happenstance.
If this streak happened on Mondays, nobody would care. But with beautiful weekdays followed by gloomy, rainy weekends — boy, does this pattern get old fast.
So, what's happening? The placement of the jet stream has been the key culprit behind our rainy weekend weather, and there are two main elements that have led to beautiful work days and lame weekends — storm track position and storm frequency.
The jet stream is a river of wind high up in the atmosphere that moves west to east across North America. The upper-level winds plug into surface storms and direct them where to go across the surface. During the summer, the warmer temperatures tend to push the jet stream to the north of our region.
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The jet stream helps direct where storms go across the country. During the summer, it is typically pushed to the north of Boston.
University of Oregon
At times, the jet stream can bend and bow north and south, looking like a radio wave across the country, and get stuck in a bowing position near New England. When the jet stream is bowed, more storms develop at the surface. This is exactly what's been happening over the past three months.
At the same time, the placement of the jet stream continues to direct storm tracks into the vicinity of Southern New England. Just take a look at the bowing of the jet stream during the nor'easter we saw in late May. Notice how it bows north towards Boston.
The jet stream bowing to the south of New England allowed for a coastal low to develop into a nor'easter in late May.
Boston Globe
Also, the Bermuda High has been stronger than average this meteorological spring and summer. A strong Bermuda High draws moisture north to support systems already on their way to the region. In the graphic below, see how the jet stream and the moisture flow from the Bermuda high align?
A strong Bermuda High has been present, often fueling the region with moisture from the southwest this spring and summer.
boston globe
This means more storms with a path close to New England, which naturally increases the number of days we can expect rain.
One extra tidbit on the science: The Bermuda High is partially responsible for the jet stream bowing towards and over New England because it's very dense and can push the jet stream to the north instead of east over the ocean. This slows down storms as they pass through New England, further increasing the chances for rain on a weekend. And get this, west of the Ohio Valley, the jet stream has been more flat than curvy.
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Think of the jet steam as a highway and storms are the cars. With a flat jet stream from the West Coast to Ohio, you can drive fast and free. When you reach a curve, you slow down. New England is in the midst of that curve, known as a trough (when the jet stream bends into a U shape).
All of these elements combined have made Boston's storm interval just two to three days this spring and summer. And more storms equal more wet weekends.
When will it be over?
The good news is that as we move into summer, the temperature contrast between air masses should decrease. That typically allows for more settled weather — or at least a longer break between storms.
There aren't any significant changes expected in the atmosphere or our seasonal patterns, like El Niño or La Niña. In fact, most weather patterns are in or near neutral phases, ironically making it more difficult to forecast seasonal weather. As of now, it looks like weekend of June 21 and 22 is trending more dry than rainy. Fingers crossed.
It all comes down to the timing of storm systems. Let's hope our luck changes and we snap the streak next weekend.
Ken Mahan can be reached at
