Sunday December 22, 2013 | 08:50 AM
Posted by David Epstein

Our warnings and advisories continue this morning across the region. Greater Portland  has not seen much in the way of ice accumulation and the power outages to the north and west remain low.  Temperatures have been sitting right at 32F for the past several hours and until these readings fall to about 30F or lower, it's difficult to accumulate ice.

As ice forms, it actually releases a tiny bit of something we call latent heat.  This is why orange growers spray their trees with water if there is going to be freeze. The heat protects the fruit.  In the current situation, as the ice is forming on trees and power lines, the heat being released is  enough actually melt some of  it  while forming.  This is especially evident around Portland where temperatures are just at freezing.  Once temperatures get under about 30F, the heat won't be enough to melt the ice and the build-up will grow.

You can find more of my forecast updates on Twitter @growingwisdom.

Timing

After a batch of  precipitation overnight and the first part of the morning, we will see periods of precipitation the rest of the day.  The next batch will be moving through around the 2PM time frame and continue a couple of hours.

 Notice temperatures as of 8AM.  If you are in an area where it is under 30F, then you have the highest risk for icing.

Overnight another area of steadier and heavier precipitation will move through the region.  Temperatures will be at or under 32F across the area, with the immediate coast the only place to perhaps stay a degree above the freezing point.

The next several images show forecast radar for the rest of the day.  Check the times carefully and remember these are forecasts for a moment in time.  In actuality, the precipitation can start and end an hour or two either side of these estimates.  However, this does give you a good idea there will be lulls in the action throughout the day and overnight.

The last batch of this should move through later Monday.

 

Why?

The reason for the icing situation is a front sitting across New England.  As warm and moist air rides up and over the cold air at the surface, it will create copious amounts of rain.  If the air at the ground is cold enough, the rain will freeze upon contact.

If the air cools enough, above the ground, then we can see the precipitation fall in the form of sleet or snow.  This will be the case over northern areas and why there is a winter storm warning there.

The front creating this mess has pushed into northern Massachusetts as is evident by the image below.  Notice how chilly it is in Boston, but how warm it is just to the west and south of the city.

Christmas forecast

Drier weather returns for Tuesday and Wednesday, Christmas Day, with highs in the 20s Tuesday and upper teens for Christmas.  There will be dry roads and bright sunshine both days so getting around should be easy, provided the ice and snow is cleaned up from the weekend storm.

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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 GrowingWisdom.com, 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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