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Dry and seasonable into the weekend followed by stormy period

Posted by David Epstein  December 13, 2012 06:30 AM

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Medium range forecasting isn't easy but actually one of my favorite time periods to try to get the forecast right. The models generally forecast out to 10 days with some going a bit longer. The best forecasts are out to 5 days and once you go beyond that the accuracy falls rapidly. The models have been advertising a storm for next week for nearly 9 days and my confidence that something will develop is quite high. However, the track, intensity and amount of cold air that will be around when and if the storm impacts New England is so much of a question it's almost pointless to try to make a forecast for next Tuesday and Wednesday. However, it's still fun to try to get it right with the best available data and you need to realize that when looking beyond a few days into the future, there will be wild swings in the forecast.
I will be sharing more thoughts on the upcoming storm on Twitter at @growingwisdomPlease find me there and follow me. I am happy to answer any questions as well.

Dry and sunny period
Before we get a flake of snow or a drop of rain we will get to enjoy three dry days of weather with nearly seasonable temperatures and mainly bright blue skies. High pressure is building in to the area this morning and any coastal clouds should move further eastward leaving those clear skies. It won't be quite as cold as yesterday as temperatures reach the lower 40s in many spots this afternoon. Friday will be even milder with a 50F reading possible early in the afternoon. Clouds increase Saturday night with snow or mixed rain and snow breaking out across the area for Sunday.

More about the storm
I think there will be bursts of precipitation Sunday through early Monday followed by a lull. Then it looks like a more significant round of rain and/or snow Tuesday into Wednesday followed by windy colder conditions later next week. Christmas eve and Christmas day appear dry, but that is really going out on a limb.nor easter December 2012.png It's hard to say how significant the event Tuesday will be, but right now that storm is the biggest potential snow and rain maker. As you always here, the exact track, timing and configuration of the storm will determine how much precipitation we get and how bad it will be when it does occur. The map you see is one possible scenario for next week's storm but it could also be weaker or move out to sea.

atmospheric Energy.png

Atmospheric Energy

In order to get a storm you have to have energy in the upper levels of the atmosphere to act as the spinning mechanism that mixes the cold and warm air. In its simplest terms a nor'easter is a big bundle of energy that is trying to mix warm tropical air with cold dry air.
Meteorologists look to the computer models to see how the pieces of energy in the flow of the atmosphere will come together and affect a particular region. The more active the pattern, the more pieces of energy that exist. Starting later this weekend there will be several bits of energy rotating around the upper level flow at around 10,000 feet. The image below shows the position of these energy pieces just prior to the weekend. The models often have a very difficult time deciding how each piece of energy will ultimately play into creating a storm. In the case of the the Sunday through Wednesday time frame next week, we know there will be several of these energy pieces, but we are not sure yet how they will play out in the forecast. The loop below shows the water vapor in the hemisphere last evening. If you look closely, you can see small spinning areas moving west to east in the flow, these are the pieces of energy we are watching. There is a HUGE storm by the way south of Greenland with a ton of energy.
sat_wv_hem_loop-12.gif

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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