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Another burst of warm weather, what's going on?

Posted by David Epstein  March 14, 2012 04:41 AM

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It seems like since we turned the clock ahead we somehow moved the seasons ahead as well. After a chilly weekend last weekend we are about to turn significantly mild again. So why do temperatures keep returning to above the long term average and will this continue through the rest of spring?

Air masses
There are a basically four air masses that affect the country at any given time. These four air masses each contain two properties, temperature and moisture. An air mass can be warm or cold, dry or moist. If you put together all the possible combinations you end up with 4 distinct air masses: air masses.jpg1. Continental Polar (cP) air originates in areas that are cold and dry. 2. Maritime Polar air (mP) originates where it is cold and moist. 3. Maritime tropical air (mT) originates where it is warm and moist. 4. Continental Tropical (cT) air originates where it is warm and dry. These four air masses bounce around the planet bumping into each other in the middle and create fronts and storms.

Season matters

The air mass is also heavily influenced by the time of year. cP air moving into our area in the summer would bring temperatures in the 70s and low humidity. In the winter cP air will often be very cold and dry.

Wind direction makes a big difference in the type of weather and especially our temperatures here in New England. These same principles apply almost anywhere in the world, although across some parts of the planet, a south wind will be a cold wind, whereas here, a south wind is warm.

Balancing the planet
Low pressure areas, or storms, try to mix up these air masses creating equilibrium. The jet stream, up at 30,000 feet, moves the air masses. Low pressure.jpg This winter, and up till now, the jet stream has been taking all the cold air across Canada and not allowing that cold air to stay in the USA very long. When the jet stream goes so far to the north, the systems at the ground tend to move mT air northward and we get mild. jet stream.jpg Since it's March, the humidity is not a factor, but, if this type pattern continued for another several weeks, we would start to feel summertime humidity very early. Notice the high pressure area off the coast in this image below. warm high.jpg That high pressure area pumps air northward and gives us mild, warm or hot air depending on the season. If you move the high into Canada, the wind direction changes to north and the pump starts moving cold air into our area. It's all about the position of these systems and the wind direction they provide.

Our computer models continue this pattern of keeping the jet stream to our north and thus the mild temperatures will continue. The next thing on my mind will be how much rain we get with these mild temperatures. The lack of snowfall and dry conditions are setting us up for a drought this summer. It's too early to predict that, but it's definitely something I will be watching.

Gardening tip of the week.
I love African violets and primrose. Learn how to care for these great flowering plants.

Follow me on Twitter at @growingwisdom and check out my latest videos at GrowingWisdom.com


This blog is not written or edited by Boston.com or the Boston Globe.
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About the author

David Epstein has been a professional meteorologist and horticulturalist for three decades. David spent 16 years at WCVB in Boston and currently freelances for WGME in Portland, ME. In 2006, More »
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