The National Weather Service has issued a WINTER STORM WATCH for much of the area from tomorrow night into Tuesday afternoon. Be prepared for tricky traveling conditions and plowable amounts of snow in some areas during that period while warming leads to transitions into various types of precipitation in other areas. After the last several benign months of March which delivered little or no snow and much above average temperatures, this one is cold and snowy but not as harsh as March 1993 when a record 38.9″ of snow fell in Boston. Will this be winter’s last gasp on the last day of winter? Astronomical spring commences at the vernal equinox at 7:02am Wednesday.

In the meantime, as a sprawling high pressure area shifts eastward across Canada and ridges into the Northeast in the next 24 hours, it will deliver some unusually cold, dry air for this time of the year. This sets the stage for the approaching storm to crank out several inches of snow before warming in the various atmospheric layers leads to phase changes of the precipitation. There are no worries tonight through the daylight hours of tomorrow so both of the Monday commutes will have dry roads. Tonight’s temperatures will decline to minimums in the teens for suburban areas with lower 20s in downtown Boston. Today’s brisk cold wind will become light and the sky will be essentially clear. Sunshine will be prevalent as some streamers and filaments of feathery clouds appear tomorrow morning. It will become cloudier in the afternoon as the wind becomes northeast to easterly at 5-10 mph. Temperatures will max out near or slightly over 32.

The storm will be developing over Delmarva tomorrow afternoon with a projected track off the southern NJ coast tomorrow night and across Cape Cod Tuesday afternoon. The system doesn’t have a rich tropical moisture feed from the Gulf of Mexico but the dynamics for atmospheric lifting will be increasing significantly early Tuesday as an intensifying upper level disturbance closes in and the warmer, more moist air rides up over the cold, dry air at lower levels. Consequently, there should be a 6-8 hour period of moderate to heavy snow from about 2AM to 10AM on Tuesday along and north of the MA Pike. South of that axis, warming will turn the snow to rain along the South Coast and Cape Cod with a gradual shift northward with arrival near the MA Pike around noon. This warming will bulge into eastern MA inside the I-495 belt during the first half of the afternoon. There could be some bursts of heavier rain through the afternoon hours in these areas causing some street flooding in poor drainage locations.

As cold air damming remains entrenched inland thanks to the cold high pressure in the Canadian Maritimes, I’m expecting a coastal frontal boundary with cold northerly winds north of the front and a milder east-northeasterly wind south of the boundary. Presently, it appears that axis could set up somewhere near or south of Boston. In any event, there are indications that a belt of sleet and some freezing rain could exist for a few hours near and north of the MA Pike up toward Route 2 in the afternoon. North of that route, it should be mostly snow for the entire storm. As a result, I am predicting a coating possible over the islands with 1-2″ over Cape Cod and along the South Coast from New Bedford to Bridgeport. North of that zone, a strip of 2-4″ from northern Plymouth County, northern Bristol County across much of RI into southern CT. Above that, a belt of 4-8″ runs through the Boston area across northwestern RI, northern CT, along and a several miles north of the MA Pike up across Cape Ann. From northwestern Middlesex County, northern Worcester County and the Berkshires into southern NH, I am expecting 8 up to 12″. Most of the rest of northern New England will receive 12″ or so with less in shadowed areas and more in the mountains of western ME into northeastern NH and over a few of the VT summits. High temperatures on Tuesday will range from the lower 30s well northwest of Boston to upper 30s near Boston to lower 40s on the South Shore to middle to upper 40s on Cape Cod. The precipitation will be ending from southwest to northeast later Tuesday afternoon. I am not expecting any significant backlash snows to roll back into the Boston area Tuesday evening. There are numerous factors weighing in on the accuracy of this forecast. Slight changes in some of the parameters may force some tweaking of the forecast on the next 24 hours.

The good news is there should be little or no coastal flooding thanks to this being the time of the month for neap tides. The 5-6 AM & PM high tides on Tuesday should not be a concern. Nevertheless, the seas will become rough and some more beach erosion is inevitable. The wind will increase along the coast to 25-45 mph with less wind inland.

Looking ahead, the storm will exit the area Tuesday night but occasional spells of snow will linger over the northern mountains much of the rest of the week which is great news for the skiers and riders. Over the rest of the area, there will be varying amounts of clouds and sunshine with a gusty breeze on Wednesday through Saturday. Temperatures will be close to a half-dozen degrees below the average for mid-late March. This is in sharp contrast to the highs of 74, 74, 67, 78, 83 and 76 degrees on March 18-23, 2012.

Melissa Mack posts her latest WBZ AccuWeather Forecast in the morning and Todd Gutner follows later in the day.

Make it a great week!



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