From the National Weather Service:
An intensifying ocean storm now appears it will track close enough to the coast for a period of heavy wet snow and strong winds to Nantucket and the outer Cape, primarily from Hyannis eastward. Unfortunately this remains a complex forecast as a small change in the storm's track will have a significant impact on snow totals. In addition, with temperatures near or slightly above freezing, precipitation may flip back and forth from snow to rain. As of now it appears 2-4" of heavy wet snow is likely across Nantucket to the outer Cape with less snowfall over southeast Massachusetts and little if any snow elsewhere. However if the storm tracks closer to the coast isolated amounts of 5 to 6 inches would be possible across Nantucket and the outer Cape. This scenario would also increase the risk of heavy wet snow bringing down tree limbs and power lines resulting in isolated power outages. Conversely if the storm tracks farther out to sea only a slushy coating to an inch would be possible. Strong northeast winds are more certain with gusts up to 60 mph across the Cape and Islands.
URGENT - WINTER WEATHER MESSAGE National Weather Service Taunton MA 357 AM EDT Sun Mar 19 2017 MAZ022-024-191600- /O.NEW.KBOX.WW.Y.0015.170319T0900Z-170319T2100Z/ Barnstable MA-Nantucket MA- Including the cities of Chatham, Falmouth, Provincetown, and Nantucket 357 AM EDT Sun Mar 19 2017 ...WINTER WEATHER ADVISORY UNTIL 5 PM EDT THIS AFTERNOON... The National Weather Service in Taunton has issued a Winter Weather Advisory for heavy, wet snow, which is in effect until 5 PM EDT this afternoon. * LOCATIONS...include the Outer Cape and Nantucket. * HAZARD TYPES...Heavy, wet snow. * SNOW ACCUMULATIONS...Of around 2 to 4 inches, with a low risk of heavier amounts up around 5 to 6 inches, mainly across the Outer Cape (Hyannis eastward) and Nantucket, with around 1 to 2 inches on the Upper Cape towards the Cape Cod Canal. Mainly on non paved surfaces, however with more intense snow with rates up to an inch an hour we`ll likely see accumulations along area roadways. * TIMING...Developing towards sunrise, continuing through midday and concluding into the afternoon hours. * IMPACTS...Heavy, wet snow combined with strong to damaging northerly winds will result in possible downed tree limbs and power outages. Visibility at times may fall as low as a half a mile. Again, with more intense snowfall we will likely see snow covered roads resulting in hazardous travel. * WINDS...Northeast 20 to 30 mph with gusts up to 50 mph. * VISIBILITY...As low as half a mile. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Winter Weather Advisory for snow means that periods of snow will cause primarily travel difficulties. Be prepared for snow covered roads and limited visibilities, and use caution while driving.