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Another winter storm is on tap for Sunday through Monday with snow, mixed precipitation and wind in the forecast. The overview has a storm moving to the coastline from the Ohio Valley during the day and then becoming a monster ocean storm Monday. The way this will unfold will bring a two-part precipitation event to the area: the first during the day and the second late Sunday night into Monday morning. The combination of these two precipitation periods will yield the snow totals you see forecast.
If the second event — the backlash snow on Monday — doesn't occur, or is weaker than expected, then the snow totals will be about half of what you see in Boston. If the backlash is stronger, my totals will be too low. Several of the models keep the backlash snow out at sea or have it occurring to a lesser extent. These situations are often very dynamic and need to almost be monitored hourly to really understand what is happening. The reason some forecasts have well over a foot of snow in Boston is due to their emphasis on the backlash snow. Others, including my forecast, are not discounting this but figuring it plays a lesser role. This is why my accumulation map may be under others.
Storm Part 1:
Snow begins Sunday morning, but won't become heavier until the late morning or early afternoon. I expect 3-5 inches of snow to have fallen by about 7 p.m. with 2-4 inches closer to the coast and perhaps as little as 1 to 3 inches over Cape Ann and Cape Cod.
Sunday evening a lull in the action will develop. This takes place as the storm originating over land transitions to the coastline and becomes more intense. As this is happening there will be a light mix of snow, sleet, rain or even freezing rain west to east across the area. I don't expect much accumulation.
Storm Part 2:
After 2 a.m. or 3 a.m. you will start to notice the wind. Radar will be picking up on new snow on the backside (western side) of the ocean storm. These snow bands will be intense and rotate through the North Shore, Boston and over Cape Cod. Do the bands hug the coast or penetrate back past Route 128? The westward extent of the bands will determine how much more snow you see Monday morning. All of this will end mid- to late-morning.
The most intense wind occurs Monday. The wind diminishes Monday evening and is actually quite light by Tuesday. Power outages are likely going to occur, but how widespread is still not known. Winds could gust over 60 miles per hour at the coast and into the 50 mile per hour range even inland.
There is a blizzard watch for the coastline. This doesn't include Boston. The watch will be converted to a warning later during the day Sunday if the chances of a blizzard increase to likely. Remember, blizzards are technical terms meaning visibility under 1/4 of a mile for three hours in a row or more due to snow and winds over 35 miles per hour.
I don't expect anything more than minor coastal flooding with this system. There will be some road closures and beach erosion but nothing out of the ordinary.
You can follow my updates on Twitter at @growingwisdom
Sunday: Snow redeveloping during the day. Rain along the coast. Rain-snow line will fluctuate. Several inches of snow.
Sunday Night: Rain changing back to snow at the coast. Snow inland. Lows 28-33.
Monday: Snow ending mid- to late-morning. Highs in the 30s.
Tuesday: Clearing and seasonable. Highs 35-40.
Wednesday: Clouding up, some light snow possible. Highs in the 30s.
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