Low pressure will race northeastward toward the area tonight, spreading a shield of snow into Southern New England later this evening…with precipitation moving rapidly across the area during the overnight hours and shifting offshore Sunday morning.
Here on the Cape, while the atmosphere will initially be cold enough to support snow, with time somewhat milder air will try and move in off the ocean – allowing snow to mix with and changeover to rain in spots later tonight. Accumulations should range from about an inch or so on the Lower and Outer Cape to maybe as much as 4 inches near the Canal.
Further to our north and west, where colder air will hang on throughout the storm, a more meaningful snow event is anticipated…with totals of 6 inches common.
The Cape – as is often the case – is a bit of “wildcard” zone with this system as we will be right on the edge of the snow/rain line throughout the storm. Some model guidance suggests the atmosphere remains cold enough to support a mainly snow event while other available tools show just enough mild air invading our area to cause the majority of the steadier and heavier precipitation to fall as rain.
There are reasons to believe both: The atmosphere itself is only marginally cold and the set-up is not particularly conducive to a big snow event – which lends credence to the rainier solutions. On the contrary, the storm is relatively weak and fast moving so it won’t have a strong onshore wind (or much time) wrapping in milder marine air. Consequently, once the precipitation starts and temperatures have fallen back to the freezing mark…they will tend to hold steady or only slowly tick upward. Likewise, bursts of heavier precipitation will attempt to keep the atmosphere cooler.
With the above-mentioned factors in mind…I’ve taken a fairly middle of the road approach with the snowfall forecast – anticipating a period of snow, which could fall moderate to heavily for a time, followed by some rain…with the best odds for prolonged rainfall on the Lower and Outer Cape.