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Bands of moderate to heavy snow south of Boston

Posted by David Epstein  March 21, 2013 10:00 PM

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Depending on exactly where you are this evening dictates just how much snow you are seeing. Some areas on the south shore are getting heavy snow, while other areas just a few miles away have lighter now. Most of the snow will be over by 2 AM, but there can be snow showers until sunrise.winter weather advisory now.png The final totals will be heaviest 30 miles or so side of Plymouth.I'll be updating my weather forecast on Twitter at @growingwisdom please follow me there. Feel free to comment or ask questions too.

Part of the overnight forecast is based on a very complicated and tricky meteorological phenomenon known as the Norlun trough. The Norlun trough is a unique area of low pressure that is actually not very uncommon. Most of you have seen the L for low pressure on the weather maps. That L represents the place on the map where the air is rising and often creating snow or rain. norlun trough.pngIf the low is close enough to our area then we get inclement weather. Often our bigger storms are the result of big low pressure centers. What is unique about a Norlun trough is that the low is very far out in the ocean and would normally be too far away to give New England any precipitation. However, in the Norlun situation a bit of the energy from the low reaches back to the west and connects with another weaker storm often over Ohio or New York. I drew a yellow line on this map to illustrate the connection between these two storms.

The snow from these bands can be very unpredictable and very narrow; you can have areas with no snow and then areas with 3-6” or more inches of snow relatively close. The entire snow area can also stay offshore and nobody sees anything. I think that is less likely. I drew a map of snow bands to indicate where the most snow will occur. As of late evening, the heaviest bands of snow are located south of Boston in Plymouth County and over the upper part of Cape Cod. The rest of the overnight forecast is a bit like forecasting who is going to get heavy rain from thunderstorms in the summer. You know how one town can be dry and other have over an inch rain? By morning, some areas will have over half a foot of new snow very close to other areas with much less.

another storm.png

I wrote this earlier today, interesting how this model is doing a great job this evening. Not to scare you folks in Plymouth County or hype up this event, but one model is forecasting some very heavy amount of snow on the order of 6-10 inches of snow. I put the actual map from the WRF model here. wrf model.pngThe reason this is a bit concerning is that this model has the ability to see small features like this trough better than bigger models. However, the model also tends to overplay precipitation, which is why I have my totals under these. This is based on these bands setting up and sitting in place for several hours from sunset tonight till sunrise Friday. This possibility needs to be evaluated later this afternoon and evening.

Friday will clear with plenty of sunshine in the afternoon. It will still be cold with highs only in the upper 30s to lower 40s.

Once the snow area moves out to see we will be enjoying a calm and tranquil weekend with highs in the 40s. Saturday will be windy, especially in the afternoon, making if feel a colder than the actual temperature.
There is the chance for more snow next week. If you did not read my blog yesterday about why this is all happening this year, click here to read more about this very wintry and cold March pattern.

Gardening this week

A very common problem with house plants is aphids. These sucking insects leave a residue on the leaves that can then cause a secondary infection on your plants. If you notice a black shoot-like coating on your houseplants, you probably have black sooty mold. This problem while not generally fatal to a plant can be an indication of an insect infestation. Check out this weeks video on black sooty mold and see if your plants have this issue.

I'll be updating my weather forecast for this week on Twitter at @growingwisdom please follow me there. Feel free to comment or ask questions too.

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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