Blame it on the Rockies


Tired of New England weather? The culprit lies 2,000 miles away.

The extreme weather here is caused by a number of factors, starting with the fact that the Rockies force some high-altitude weather anomalies down into the warm, moist air of the Gulf of Mexico, said Lodovica C. Illari, lecturer in earth, atmospheric and planetary sciences.

In an April 30 talk sponsored by the MIT Activities Committee (MITAC), Illari, a researcher in large-scale dynamics and synoptic meteorology, offered an understanding of why New Englanders sometimes have to keep their winter clothing handy until summer. Synoptics is the study of the methodology of weather systems.

Several kilometers above our planet, there is a phenomenon called the tropopause that occurs where the stratosphere meets the Earth-engulfing troposphere. Any dip in the tropopause can cause a strong upper-level cyclone.

When this happens, we at ground level are blissfully unaware of it. But when this dip gets pushed south by air currents off the Rockies and sucks in warm air from the Gulf of Mexico, a nor'easter is brewing and we're in for trouble.

This happened in the Blizzard of 1978 and the storm last February now dubbed the President's Day Storm. An upper-level cyclone made its way over Florida and then up the coast, meeting cold air when it hit the Massachusetts land mass. The moisture in the upper levels condensed, turned to liquid and then snow. And all because the Rockies helped the tropopause dip down out of its usual middle latitudes, 27.5 inches of snow dropped on Logan Airport.

In the Blizzard of '78, snowfall in Boston was lower, but up to 36 inches fell in surrounding areas. That storm was accompanied by hurricane-force winds, which caused some of the major drifts that stopped cars dead on Route 128 in a matter of hours.

In the "Perfect Storm" of October 1991, snow was not a factor. There, an upper-level cyclone happened to coincide perfectly with a surface cyclone called Hurricane Grace, creating a rare but deadly confluence of two strong weather anomalies.

While the Atlantic storms blow out to sea and "decay" over London, Pacific storms decay over Seattle, creating the frequent cloudy and rainy weather in those cities.

"New England is one of the strongest regions of cyclone development," Illari said, and because of this, it's one of her favorite regions in which to live and study the weather. Originally from northern Italy, Illari said she has lived here for 10 years, as well as in England for a time. "New England weather is best," she said. "There is no relaxing. We're in a very active region of the globe."

For current conditions and links to forecasts, check out the website of Illari's research group, the Synoptic Dynamics Laboratory of EAPS' Program in Atmospheres, Oceans and Climate:http://8.83.2.130/paoc/about/syn%5Flab.htm.

A version of this article appeared in MIT Tech Talk on May 7, 2003.


Topics: Earth and atmospheric sciences

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