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Temperature roller coaster continues and a look at Monday storm chances

Posted by David Epstein  March 14, 2014 08:07 AM

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There’s a term some meteorologists use called “model hugging”. Basically, this means buying those models you hear so much about hook, line and sinker. The thing about the models, they are guides to what will happen in the future, not gospel.

Any model is not 100% correct, just ask an economist. When I forecast a storm I certainly review all the models, but ultimately I have to make the call myself. When it's three or four days before a storm the models often are still all over the place predicting how the atmosphere will come together.

The models are amazing and it’s a wonder to me we can forecast the formation of anything 10 days in advance. Yet, they often don't have the accuracy needed for a confident forecast more than 72 hours ahead of time. This is why you hear so many "ifs" in the long range.

On a planetary scale, knowing a storm will form is important, but to get the forecast right for an area Cape Ann to Cape Cod and back to the Berkshires, the model has to predict the track of a storm within 50 to 100 miles otherwise the forecast won’t be accurate. The model could show a storm's track correctly 10 days in advance, but the odds are much higher it will do so 2 days before an event.

The basic way the models work is weather balloons are sent up from weather offices across the globe twice each day. The map below shows where these balloons, known as radiosondes, are launched.(just USA stations) This gives us a good picture of what the atmosphere looks like right now. That information is given to computers where physical and mathematical equations move the picture of the current state of the weather ahead in small time steps. Some models keep doing these steps to eventually predict 16 days into the future. The further ahead in time you go, the better chance the model will have errors. While climate models are somewhat different, they too predict far in to the future and the further out you go, the less accurate those forecasts, but that’s for another discussion.
weather ballon stations.GIF
The models show agreement for the next couple of days. Today is certainly milder with highs in the 30s. There will still be a busy wind from the northwest, so it feels colder than the actual temperature indicates.

Overnight as even milder air streams north a quick shower could fall. These could last into the first few hours after sunrise, but the trend will be for increasingly sunny skies and a milder afternoon. Highs will reach the upper 40s and lower 50s with some towns hitting a bit higher southwest of Boston.

As another cold front crosses Saturday night it’s back to the deep freeze for a few days and a renewed chance at another snowstorm.

cold again.png

Another Snowstorm
Storms love to form on the boundary between arctic air and milder air with more moisture. All the models agree there will be a storm forming on this boundary Sunday and Monday. Similar to a storm 10 days ago, if the cold air pushes far enough south, the storm will ride the boundary of the cold air and stay south of New England. However, if the cold air doesn't move as far south, it paves the way for the boundary of air masses to be much closer and therefore the snow to fall over our region.

I put only two tracks on the map below. The closer to the northern track any storm takes, the more snow we could see. If the storm stays closer to the southern track, it will pass safely out to sea with little or no snow at all.
Monday storm.png

Back in 1956 Blue Hill Observatory recorded 12.6 inches of snow on Saint Patrick’s day and in 1993 Boston plowed over 3 inches of snow on the same date. Both years were cold and snowy ones for New England. In 1956 another storm brought over a foot of snow on the 19th in the final hours of winter.

Over the weekend forecasters will be watching the models closely and those of wishing for spring will also be hoping for a bit of Irish luck.

I’ll be updating the forecast on Twitter @growingwisdom.

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 »
Boston Forecast & Weather Tracker - Storm Center
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