Thursday December 19, 2013 | 07:19 AM
Posted by David Epstein

This time of year cold air is very powerful. The next four to five weeks are really the heart of winter cold.   The strength of the cold air is an important player in the upcoming forecast into the weekend.

There is going to a be a frontal system, along a very strong jet stream, dividing deep winter cold from spring-like warmth cutting through New England this weekend. Because of where we sit in the country, Maine will most likely stay on the cold side of this boundary all weekend.

You and your friends might head to Cape Cod for Saturday or Sunday where winter golf will be played and I expect courses to be full. Here in Maine, temperature will be in the 20s and 30s this weekend with clouds and periods of precipitation.

Warm air is lighter than cold and while it's still winter-like here at the surface, the warm air is going to pour on top of the cold layer all weekend long. This scenario of warm air over cold air creates a situation known as overrunning. This is the perfect set-up for sleet and freezing rain, the latter of which can cause tremendous problems.

Starting early tomorrow, little waves of low pressure will bring periods of snow, sleet, freezing rain and rain to the area through Sunday. While it won't be precipitating the entire time, there will be little or no sunshine and the chance for some form of moisture much of the time. The most likely periods of some freezing rain/sleet/snow will be early Friday morning and a few hours Saturday, but the main thrust of precipitation holds for  Sunday. The timing of this situation isn't well known as the jet stream is undergoing a big shift and moving very quickly.

One thing I advise you to do today is buy an extra bag of ice melt. I am not forecasting a situation similar to 1998, when a major ice storm shut down much of the central and southern part of the state. Further, I don't want to over hype a storm. However, freezing rain, even a small amount,  can make walking nearly impossible. If you don't have ice melt on hand or the stores run out, it can be a real issue. If you keep it in a dry place it won't collect into a ball of unusable hard mess for a while.

Take a look at the two maps below. They are both for the same time late Saturday. The first map shows temperatures at the ground. Notice extreme southern Maine is forecast to be well above freezing.  


Now review the second map. That map is a forecast of temperatures at about 5,000 feet, or just below the summit of Mount Washington. The numbers are in degrees Celsius. I have converted to Fahrenheit in the notation around Brunswick. Temperatures are quite uniform from Portland to the foothills. Notice places around Gray, Augusta, Waterville are in the 20s at the ground but the air above them is well into the 40s. Problems  arise because precipitation that falls through the  warm layer will do so as rain until it hits the ground and freezes into ice.

What I will be working on the rest of the week is how much precipitation will fall, what type and giving you a better idea of when each wave of this stuff will come through. Remember, cold air is very dense and powerful and unfortunately can get stuck at the ground to create these potential ice storms. Just don't panic, I'm letting you know early our situation for later this weekend. I'll be giving lots of updates here and on Twitter @growingwisdom as the situation unfolds.


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About the Author

David Epstein has been a meteorologist for more than 25 years. He spent 16 years in Boston and currently freelances at WGME13 in Portland.

In 2006, David founded, a business producing educational and marketing videos for the green industry. He currently is a professor at Framingham State College, teaches Jan Plan at Colby College and owns Bloomscapes Inc., a landscape design business.

David authored "Gardens Of New England" and his work has been published in Grolier's Science Annual for 10 years. He lives in South Natick, Mass., and has a summer home in Harpswell.

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