DAYS 1-5 (JANUARY 18-22)
This weekend marks the in-your-face portion of a weather pattern shift. Today will be a milder day with a southerly air flow freshening ahead of an approaching cold front, which will result in rain showers for our region late in the day and this evening. A period of partial clearing and the start of a chill down follows this overnight into Sunday, setting the stage for the second round of unsettled weather from late afternoon Sunday to early morning Monday. This will come as a batch of precipitation associated with a wave of low pressure moving swiftly northeastward along the frontal boundary that will then be offshore. The low will be starting to deepen fairly quickly as it passes by, and this combined with its precise track results in a tricky-to-forecast rain/snow line to start and a range of snowfall amounts. The low’s track will be close enough for the precipitation to start as rain from the South Coast of New England to the South Shore of MA, and snow elsewhere, but with the rain/snow line then shifting southeastward so that the areas that start as rain flip over to snow. To the west of the I-95 belt where there is nothing but snow and the atmosphere is coldest, snow amounts will be greatest, and areas that start as rain then turn to snow will have lesser overall snow accumulation in the end due to less time to accumulate, and wetter snow when it is snowing. If you have read my previous commentary you may have seen my initial snowfall forecast for this system was widespread 3 to 6 inches with 1 to 3 inches over Cape Cod and the Islands. The update today makes a few changes to this since we’re close to the event and can pinpoint a little more. I’ll trim back the eastern portion of the 1 to 3 inch area to limit accumulation to about 1 inch over Outer Cape Cod and Nantucket, 1 to 2 inches for Martha’s Vineyard and Lower Cape Cod, 2 to 4 inches for the remainder of the South Coast region up through the MA South Shore, 4 to 6 inches in the I-95 belt, and a bump-up in expected snow amounts to 6 to 8 inches west of the I-95 belt. This event wraps up first thing Monday morning as the last of the snow exits the coast around sunrise. This will be followed by plunging temperatures with a surge of arctic air that comes in Monday and lasts into the middle of next week, but with dry weather. Another low center will pass not-too-far southeast of New England by Wednesday, but the snow shield from that stays offshore.
TODAY: Limited morning sun, then cloudy. Rain showers arrive from southwest to northeast late-day. Highs 40-47. Wind S increasing to 10-20 MPH, higher gusts at times especially South Coast and higher elevations.
TONIGHT: Overcast with widespread rain showers and areas of fog evening. Breaking clouds, dissipating fog overnight. Lows 33-40. Wind S 5-15 MPH shifting to W.
SUNDAY: Limited sunshine in the morning, thicker overcast afternoon. Snow arrives by late-day except rain southeastern MA / South Coast regions. Highs 35-42. Wind W up to 10 MPH shifting to N.
SUNDAY NIGHT: Overcast with snow except rain/mix changing to snow southeastern areas. Expected snow accumulation by dawn – coating to 1 inch Nantucket and Outer Cape Cod, 1 to 2 inches Martha’s Vineyard and Lower Cape Cod, 2 to 4 inches remainder of South Coast to MA South Shore, 4 to 6 inches I-95 belt, 6 to 8 inches west of I-95 belt. Lows 17-24 except 24-31 far southeastern areas. Wind N 5-15 MPH, a few higher gusts eastern areas.
MONDAY (MLK JR DAY): Sun/cloud mix. Highs 25-32 early, then falling through 20s. Wind N to NW 10-20 MPH, higher gusts.
MONDAY NIGHT: Clear. Lows 3-10. Wind NW 5-15 MPH, higher gusts.
TUESDAY: Sunny. Highs 13-20. Wind NW 5-15 MPH, higher gusts.
TUESDAY NIGHT: Mostly clear. Lows 2-9. Wind NW 5-15 MPH.
WEDNESDAY: Sun and high clouds. Highs 15-22. Wind NW 5-15 MPH.
DAYS 6-10 (JANUARY 23-27)
While the coldest air eases early in the period the pattern holds below normal temperatures in place. An additional snow threat exists in the January 24-25 window and again about January 27. Magnitude of threat(s) and details TBD.
DAYS 11-15 (JANUARY 28 – FEBRUARY 1)
One or two additional opportunities for snow in a continued cold pattern to end January and start of February.