DAYS 1-5 (DECEMBER 4-8)
A cold front slips by today and low pressure develops on this front to our southwest, quickly organizing and strengthening as it tracks northeastward through Saturday, the center of a rapidly deepening low likely passing just southeast of Cape Cod Saturday night. For us, this will be a quick-hitting but fairly potent late autumn / early winter storm, starting as rain for all, from the South Coast this evening northward overnight into Saturday morning. As the storm center deepens and makes its closest pass then starts to pull away toward the Gulf of Maine, colder air will be drawn in from the north, and additional cold air will be generated aloft by the deepening process and brought toward the surface by the process of dynamic cooling (in which moderate to heavy precipitation drags the cold air down with it). This will change the rain over to snow, first during the midday hours of Saturday in the hills of southwestern NH and north central MA, then toward lower elevations and southeastward so that most areas with the exception of Cape Cod, the Islands, and the immediate South Coast will see snow before the precipitation exits in the early hours of Sunday. The highest snowfall amounts are likely to occur in areas that changed over first, as well as a band of more intense snowfall where the right combination of “just cold enough” and heaviest precipitation occurs. As the storm exits and moves away during Sunday, we’ll see windy and cold weather with a few snow showers possible in an otherwise blustery sun/cloud mix kind of day. Winds will quickly drop off Sunday night and early Monday as we get into a very weak ridge of high pressure between the departed storm and an evolving storm south of New England, which may graze the region Monday night and early Tuesday with some precipitation, although most indications are that this system will remain largely offshore. Still, we should keep an eye on it as it would not take much to “happen” in the atmosphere to draw it closer to this area. Later Tuesday, that storm will also be pulling away, leaving us with dry and chilly weather.
TODAY: Partial sun through lots of clouds morning. Cloudy this afternoon. Highs 48-55. Wind SW 5-15 MPH, gusts 20-25 MPH.
TONIGHT: Cloudy. Rain South Coast evening, spreading north overnight. Lows 40-47. Wind SW 5-15 MPH with higher gusts, shifting to N.
SATURDAY: Overcast. Rain all areas morning, changing to snow from northwest to southeast in all but the South Coast region during the afternoon. Temperatures falling to 28-35, coldest in southern NH and central MA, by the end of the day. Wind NE to N 10-20 MPH except 15-30 MPH Cape Cod with higher gusts possible in all areas, but especially coastal areas and higher elevations.
SATURDAY NIGHT: Overcast evening with snow, possibly heavy at times, except just rain mixing with snow South Coast, ending from southwest to northeast late evening and overnight followed by partial clearing. Accumulation of snow – slushy coatings South Coast, 1-3 inches Cape Ann southward along the immediate shoreline through Boston to the South Shore westward to Providence, 3-6 inches from the NH Seacoast down the northern portion of the I-95 belt to I-90 then westward from there into south central MA and eastern CT as well as northwestern RI, and 6-9 inches from the Merrimack Valley and interior southern NH through north central MA. Lows 25-32. Wind N to NW 10-20 MPH with gusts 25-35 MPH.
SUNDAY: Cloud/sun mix. Passing light snow showers possible. Highs 33-40. Wind NW 15-25 MPH, higher gusts.
SUNDAY NIGHT: Mostly clear. Lows 18-25. Wind NW diminishing to under 10 MPH.
MONDAY: Partly to mostly cloudy. Highs 31-38. Wind variable up to 10 MPH.
MONDAY NIGHT: Cloudy. Chance of snow/mix/rain favoring the South Coast. Temperatures steady in the 30s. Wind NE 5-15 MPH.
TUESDAY: Cloudy start with a chance of snow/mix/rain favoring Cape Cod, then clearing. Highs 35-42. Wind N 10-20 MPH.
DAYS 6-10 (DECEMBER 9-13)
High pressure brings dry but seasonably chilly weather for December 9. Disturbance from the northwest brings a rain/snow shower risk December 10 with a brief shot of milder air then a shot of colder air with dry weather December 11. A frontal boundary and possible low pressure system brings the threat of unsettled weather back for late in the period, December 12-13, but this is low confidence based on questionable performance of guidance.
DAYS 11-15 (DECEMBER 14-18)
Keep this a low confidence general outlook for a somewhat active pattern with 1 or 2 precipitation threats and variable temperatures averaging near to below normal.