DAYS 1-5 (FEBRUARY 15-19)
A winter storm will impact the region for the vast majority of this 3-day weekend in a variety of ways. There are a lot of parts and interactions here so I’ll break this down the best way I can for you to understand my expectations. First, we have high pressure across a good portion of central and eastern Canada, with an extension down across New England to start today. The main center of this high will remain in central Canada, with a weaker extension to the east. This limits the influence it can have on our upcoming system, but it will be strong enough to hold cold air in at the surface, away from the immediate coast, which will be a significant player. The weaker southward extension of the high allowed it to get quite cold overnight (generally 10s to lower 20s for low temps), and this high also allows us to start the day with filtered sunshine. But as low pressure makes a trek out of the Ohio Valley / eastern Midwest toward the interior Northeast, and a warm front extends ahead of it, to our south, we’ll have an increasing and thickening of the overcast as the day goes on. From the end of the afternoon through early evening, a snow shield will spread from west to east across the region. It will at first bit a little patchy, having to overcome dry air, but this process will actually chill the atmosphere a bit more, assuring several hours of accumulating snow across the region before the next phase of the storm begins. That phase will be a mid level jet stream bringing in warmer air aloft, where the precipitation develops. As this takes place, a change over from snow to sleet / freezing rain / rain will occur from south to north, starting at the South Coast in the overnight hours, and progressing northward. The atmospheric temperature profile determines sleet vs. freezing rain vs. liquid rain, and the overall outlook of how this goes hasn’t really changed from yesterday’s outlook. I do think we’ll see a ribbon of sleet for most areas initially, but this will likely be for a limited time as the warming aloft is substantial enough to erode the cold air low enough to prevent full freezing of rain drops after a short period of time. The key then becomes the surface temperature as the rain area expands. Across the South Coast, Cape Cod, and up along the coast of the MA South Shore, I expect the surface temperature to rise above freezing to prevent a freezing rain situation. This should also happen up the coast from Boston to the MA North Shore, but may be delayed for a while, so that a period of freezing rain can occur here. As soon as you go inland, and especially progress further inland, the freezing rain will be more prevalent, and may continue for most of the event. There are areas that may never get above freezing – these favoring the elevated valleys of northern Worcester County, maybe western and northern Middlesex County of MA, and interior southern NH. The warm front associated with the primary surface low, which by the early hours of Sunday will be entering NY State, will be the focus for a secondary low pressure area, developing in the vicinity of the South Coast of New England. As this takes place, the only place that likely gets into the warm sector of the system will be Cape Cod and the Islands. The colder air will never have been eroded efficiently enough elsewhere to allow that boundary to progress to the north, and once the secondary low forms, and moves east northeast, it will drag that boundary back to the southeast anyway. The structure of the storm associated with the primary low will remain fairly intact, however, even as the low itself decays. This may send a dry slot into southeastern MA and RI, limiting some precipitation during the plain rain portion of the storm. But one last burst of moderate to heavy rain will cross the region later Sunday as the occluded / cold front passes. This burst should be in liquid form for the majority of the region, but in those valley areas to the northwest there is still the potential for this to be in the form of freezing rain, which would add enough ice accretion for tree damage, if it should occur this way. Will watch for that. A little wrap-around moisture can send some sleet and snow showers back across the region as the cold air returns quickly behind the departing storm, as the new low takes over in the Gulf of Maine and starts to intensify rapidly. I don’t think much in the way of sleet/snow accumulation will occur with this parting shot, but a quick coating can occur in some areas. And no, I did not forget to talk about the pre-change-over snow accumulation forecast. That remains basically unchanged from my previous discussion. The expectation is 1 to 3 inches across the South Coast, least on Nantucket / Outer Cape Cod – with much of this melting away on Sunday as this is the area most likely to enter the warm sector briefly. Elsewhere, expect a general 3 to 6 inch snowfall from the MA South Shore to interior RI and northward from there, with much of this becoming compacted by rain and temps in the 30s to lower 40s, or further inland compacted and acquiring a coating of ice where freezing rain occurs. Exception remains some 6 to 8 inch snowfall potential across interior southern NH and north central MA, particularly the higher elevations, where the snow will be less wet and last longest before any change-over, but sleet and freezing rain compaction will occur in these areas as well. Post-storm, we have a wind event to deal with on Monday. The low pressure area will become a powerhouse as it moves from the Gulf of Maine into Atlantic Canada, and its circulation, in contrast with central Canadian high pressure extending into the Great Lakes and Ohio Valley, will create strong northwesterly winds here, with gusts above 45 MPH likely in much of the region, including the potential for wind damage and scattered power outages. Areas with ice on the trees will be particularly vulnerable. This will come along with the return of a pretty cold air mass too. While the wind eases slightly Tuesday, it will continue to be quite gusty, making the already below normal temperatures feel even colder, though the weather will be dry. Wednesday will also be a cold, but more tranquil day, as high pressure dominates.
TODAY: Filtered to dimmed sun as high clouds thicken up in the morning. Lowering overcast afternoon – late day snow likely, especially west of I-95. Highs 23-30. Wind N up to 10 MPH.
TONIGHT: Overcast. Snow evening into overnight with accumulation of 1 to 3 inches South Coast and 3 to 6 inches elsewhere except 6 to 8 inches in some locations of southern NH and north central MA. Snow to sleet to freezing rain / rain transition begins south to north late evening / overnight with icing conditions first away from the immediate South Coast up to the I-90 belt with higher probability to sleet to the north. Temperature rising slightly to 28-35, mildest along the South Coast. Wind N up to 10 MPH evening, staying that way over interior valleys and shifting to E 5-15 MPH elsewhere, especially coastal areas, overnight.
SUNDAY: Overcast. Precipitation continues – transition from freezing rain to non-freezing rain works from South Coast into the I-90 belt but takes longest in valleys, sleet to freezing rain in areas to the north with a lower chance of getting to non-freezing rain, resulting in additional sleet accumulation and ice accretion. Rain may taper to just drizzle / few showers southeastern MA and RI for a time during the afternoon hours. Highs 30-37 southern NH & interior MA, 38-45 eastern coastal MA & RI, 45-52 Cape Cod / Martha’s Vineyard / Nantucket. Wind E to SE 5-15 MPH coastal areas, variable under 10 MPH inland areas, briefly becoming S 10-20 MPH Cape Cod region and variable 5-15 MPH elsewhere before shifting to W from west to east end of the day.
SUNDAY NIGHT: Cloudy evening with one more burst of widespread rain showers except potential icing interior elevated valley locations early evening and potential sleet/snow showers late evening. Breaking clouds overnight. Lows 15-22. Wind W to NW increasing to 15-25 MPH, higher gusts.
MONDAY (PRESIDENTS DAY): Sun/cloud mix. Slight chance of a passing snow flurry. Highs 25-32. Wind NW 15-30 MPH, gusts 35-55 MPH.
MONDAY NIGHT: Partly cloudy. Lows 11-18. Wind NW 15-25 MPH, higher gusts.
TUESDAY: Partly sunny. Highs 21-28. Wind NW 10-20 MPH, higher gusts.
TUESDAY NIGHT: Mostly clear. Lows 8-15. wind NW 5-15 MPH, diminishing.
WEDNESDAY: Mostly sunny. Highs 26-33. Wind N up to 10 MPH.
DAYS 6-10 (FEBRUARY 20-24)
Watching a snowstorm potential in the February 20-21 time frame – leaning toward an offshore evolution and more of a side-swipe than a bigger hit, but the latter cannot be discounted as a potential. Fair weather returns after. Temperatures below normal.
DAYS 11-15 (FEBRUARY 25 – MARCH 1)
Watching the February 26-28 period for a potential winter storm impact. Temperatures below normal.
… Wednesday will be another cold day, but more tranquil as high pressure replaces the northwest air flow of the previous two days. Then, attention turns to Thursday’s storm threat. The key for this event is the track of a low pressure area developing down the coast. This system takes on more of a “classic” look as it forms and moves seaward, and at this point I am still leaning more toward a side-swipe rather than a direct hit. Further elaboration on this system will begin with tomorrow’s update.