Yesterday Portland reached 50 degrees, just one degree shy of the record high for the date. Interestingly enough, this occurred on same day when day back in 1943 Portland set its all-time lowest reading ever at 39 degrees below zero.

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This past weekend temperatures fell well below zero and the highs on Sunday remained below 10 degrees across the area. This winter we haven’t seen a prolonged period of snow or cold and just when winter seems to set in, another push of mild air arrives.

It can be tempting to start pointing fingers as to the cause of individual wild weather swings, but the atmosphere is very complex. There are, however, model simulations which do predict more arctic air spilling south into the mid-latitudes, such as here in New England, as the climate warms.

A Decade Of Heavy Snow
Of course snowy and bitter cold weather often brings the standard joke about how a warming climate can produce more snow and cold. It seems counterintuitive to be snowier and colder, doesn’t it? During the past decade snowfall has increased along with large precipitation events.

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The chart below shows how much snow fell during every winter since 2004. Average snowfall in Portland is about 75 inches during this period, an increase over the 140-year average. Why the increase? Many climatologists believe the added accumulation is because warmer air holds more moisture — and more moisture means more snow. Even an overall warmer planet won’t be hot enough for decades — or even a century — before yearly snowfall decreases.

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Snowfall has increased during the core winter months, but it has decreased on the margins in October, November and April. This makes some sense. As the earth warms, the first months to start losing snow would be those in the fall and spring. Eventually temperatures will warm further and we’ll get less snow from December through February.


Colder Blasts In A Warmer World
What about the cold weather? How can it be colder in a warmer world? First, remember that a warmer world still has a lot of cold at the top and bottom of it. Typically, the polar vortex spins around really fast and keeps much of the cold air locked in across the northern part of the planet. When the vortex weakens as it did last week, it allows the cold air to propel itself southward.

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The loss of sea ice across the arctic is well documented. Again, researchers have found the loss of sea ice can dramatically influence the polar vortex which, in turn, influences climate variability.

The loss of sea ice is just one of many factors shaping the polar vortex. Snow cover across Eurasia, El Nino and Southern Oscillation and the fluctuation in solar activity all impact seasonal weather variability. How these variables interplay with shorter term changes, such as equatorial thunderstorms and pressure patterns in the Pacific and Atlantic, haven’t been systematically researched.

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What’s become quite clear is that our highly erratic New England weather will continue, but the ride up and down is looking steeper and more inconsistent than ever recorded.

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