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Mixed Bag Of Precipitation Ends As Snow Late At Night

Evening Update:

As expected the sleet line is pushing west towards Route 495 and will be causing areas with all snow to mix with and perhaps change to all sleet. This will cut down on snow amounts.

The precipitation can be traced all the way down the coastal plain until just north of Washington, DC.

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The highest snowfall totals will be in the higher elevations of Worcester County. The sleet will last until a few hours before midnight and then change to snow before ending. Since sleet is so much heavier and denser than snow the snow won't pile up as high as it could in northern areas of Worcester County and southern New Hampshire.

Cape Cod Rain

Wind and rain will continue for a few hours over Cape Cod and the Islands. A dry slot might end the rain for a few hours later this evening, but the wind will continue. Wind could gusts up to 50 miles per hour and a scattered power outage is possible.

Here are some of the higher snow totals as of early evening.

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Earlier Update

I updated the snow map a bit for the latest conditions scroll down to see the latest predictions.

As of late morning snow was falling from Washington, DC to just west of Philadelphia to New York City and western New England. The blue areas on the radar map are snow.

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Here's a radar projection for 7PM this evening. The blue area is snow the green is rain and the purple is a mix. The mix is actually expanding westward late this afternoon and this evening meaning many areas who are getting snow early this afternoon will actually change to a mix and amounts will be cut down.

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Earlier Blog Entry Below

Mild air is going to win out for most of this storm. This means across eastern Massachusetts and much of eastern southern New England, this is primarily a rain or mixed precipitation event.

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I was very concerned about the warm air yesterday and most of the models have now trended warmer, especially at the upper levels of the atmosphere.

Letís go through a series of maps which will help explain my thinking. The first map is the timing of the change to mix or snow. Just because you see snow mixing in doesnít mean it will accumulate. Many areas will waffle back and forth between rain and snow for many hours. At times you might see a slushy coating and then it could melt as the rain takes over. Some sleet pellets can also work into the system. Those are the little balls of ice many people call hail, but itís not, itís sleet.

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The next map shows how much snow I am expecting. If you asked whatís making me nervous this morning itís warm air coming in at the higher levels of the atmosphere and causing a flip-flop of rain and snow for so much of the storm very little snow ends up actually accumulating.

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In the Route 495 belt you might see the precipitation start as rain, flip to snow then back to sleet and finally end as some snow. All these changes to precipitation type mean the forecast is exceedingly difficult.

Iíll be updating on Twitter and here as I receive new data.

Warm Air Problems
This next map gives a temperature forecast at 10,000FT later today. The numbers are in degrees Celsius, so anything above 0 is above freezing. This means as the snow falls into this layer itís going to melt. Let see what it looks like below this level.

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This next image is for 850 millibars in the atmosphere or close to a mile high. At 5000 feet itís cold enough for snow, but since itís so warm above, the melted snow will refreeze into sleet. This means little ice pellets. Once a snowflake melts it canít become snow again no matter how cold it gets.

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As the storm pulls north of the region cold air will finally win out and the rain will end briefly as snow in most locations. As temperatures fall below freezing I expect some icy spots to develop late tonight and tomorrow morning. The rest of Thanksgiving will feature a lot of clouds, blustery and chilly readings and just the chance of a snow shower.

Black Friday is cold and dry and that weather continues into Saturday. On Sunday a milder flow of air will help boost temperatures back near 50F so those of you who do see snow accumulate will see much of it melt
Have a great day.

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