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Too much warm air will leave area icy or wet not white

Posted by David Epstein  December 16, 2012 08:00 PM

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In order to get a big snowstorm you need warm air. You might think that statement is counterintuitive but it's true. The biggest snowstorms that hit our area have some very warm air quite close. snowstorm development.png The warm air is what usually contains the moist part of a snowstorm and the cold air gives the storm its chill so the precipitation falls as snow, not rain. The deeper into winter we go the less likely rain will fall and the chances we get snow during our storms increase That fact is one of the reasons why February is our snowiest month. This week we have several storms affecting the area, however, the amount of cold air just isn't going to be enough to give us much if any snow. The above diagram shows the breakdown of precipitation with a storm that tracks along the coast. If the storm tracked further east, the snow line would also move east, a more westward track would bring the rain further inland. I don't see us having a classic snowstorm track with any of our storms this week.I'd love to have you follow me on Twitter at @growingwisdomI tweet more information about storms there as well.

Overnight
There is a huge contrast in surface temperature tonight. Areas at the coast are above 32F and areas inland well below that mark. Slippery travel will occur overnight mostly well west and north of Boston in that colder air. There is going to be some snow but nearly all of it will fall to the north of Massachusetts. winter weather  advisory.pngWhile this is not a snowstorm, we can see hazardous travel. Now, this doesn't mean that some of you that live along the New Hampshire border might not see an inch of the white stuff, however, for the most part, too much warm air has already moved in at cloud level for snowflakes to form. As the precipitation falls into cold air at the ground, it freezes into sleet or freezes on contact as freezing rain. There is a winter weather advisory in effect for much of the area west of Route 495 for slippery roads overnight and into early Monday. The problem is that the cold air will remain at the ground even as it becomes to warm at cloud level to snow. overrunning.png What we have is a warm air riding up and over cold air trapped at the ground. The diagram shows what is happening tonight. The areas that are getting rain are places like Boston, New York, and the coast of Maine, further inland we have freezing rain and even further north, in the mountains, we have snow.

StormTotalSnowFcst.png

Monday-Friday, storms two and three
Monday, the first round of precipitation will be moving northward and we will get into a bit of a lull. This lull lasts through the Monday evening commute before more rain and some wind move into the region. We could see heavy rain overnight Monday and into early Tuesday. During the day Tuesday the rain will become more showery in nature and will continue that way into early Wednesday.
I then expect another break later Wednesday into Thursday before the third system influences our weather late next week. Again, track, amount of cold air and strength of the storm will all determine how this third and final storm before Christmas will affect New England. Right now, it looks too warm in southern areas to see any snow with storm number 3, but it could be a very snowy period for the ski areas of the north.

Newsletter
Every few months I write a newsletter on gardening and a bit about weather. You can see the newsletter for December by clicking here. You can sign up for the newsletter at Growing Wisdom. It's free and no one else gets the email addresses.

Caring for poinsettias
If you love these traditional Christmas plants there are a few things you can do to keep them looking great into and beyond 2013.


I'd love to hear your thoughts on this blog or any others. Please 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.
The author is solely responsible for the content.

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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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