All week long, we've been watching how a developing coastal storm and a weakening clipper system would interact. More interaction early on would have led to a decent thump of snow for much of New England. Instead, these two systems will only interact a little, bringing light snow showers and light accumulations to parts of the region. This will occur throughout the day Friday, but snow showers will become the most widespread later in the afternoon and evening.
As for specific timing, ocean-effect rain and snow showers will be possible along the Massachusetts coastline throughout the day. Snow showers across the interior from the clipper system will likely arrive in the early afternoon. The outer edge of precipitation from the coastal storm will likely arrive around mid-afternoon and last through the evening as it takes an outside-the-benchmark track.
Below: HRRR showing potential weather around mid-afternoon today:
This evening is when snow will likely be the most widespread. The immediate coast and South Shore will likely see rain showers or mixing at the start before the rain/snow line begins to drop south and back toward the immediate coast. Snow will wrap up in the evening from west to east for much of New England. Maine will see snow from the coastal storm in the evening through the first part of the overnight.
Below: HRRR showing potential weather this evening (1st image) and late tonight (2nd image):
When all is said and done, a widespread coating to 3 inches of snow will likely have fallen across New England. The areas with the best potential to reach that 3 inch mark will be interior eastern Massachusetts and Downeast Maine. Southeast New Hampshire is a bit of a wild car and could end up with more than an inch, though we've kept them in the up to 1" zone due to the uncertainty. This will be a light and fluffy snow for most, with ratios of 15-20:1 across the interior. It will be a wetter snow near the coast.
There are some uncertainties in the snowfall forecast, but no matter how these factors end up going, it will be a minor event. These uncertainties include how far inland the higher moisture from the storm can push and the timing of colder air rushing southward during the day. If the cold air rushes south too quickly, it will dry out the air and lessen snowfall rates for southern New England. If it takes too much time, most of the event will be rain and mixing.
Across Maine, the exact track of the nor'easter will be critical in how close the heavier snow gets to Downeast Maine. The storm will be well south of the Maine coast, but it is a big storm in regards to size. As the storm heads northeast into Nova Scotia, some of the precipitation will likely wrap around the storm into eastern Maine. The question is how much and far east the snowfall can push back into eastern Maine.
Below: Probability of at least 4 inches of snow across Maine:
Another factor to watch will be the potential for a period of enhanced snowfall rates across interior northeast Massachusetts and southeast New Hampshire. A coastal front will set up in this area this afternoon, separating the sub-freezing air from the above freezing air. The front will collapse southward as the evening goes on.
This coastal front could provide increased forcing for snow showers with more snow falling near the front as opposed to areas farther north and farther south from it. The area along this front early this evening will have the best chance at 2-4 inches of snow. This area appears to be interior northeast Massachusetts.
Once this system passes, it will swing the door wide open for very cold air to sweep into New England. Broad cyclonic flow will allow for continued scattered snow showers on Saturday, mainly across interior New England. Strong Canadian high pressure builds for later Saturday into Sunday, helping to usher in the arctic temperatures.
The coldest day of this stretch will be Sunday. Temperatures around 5,000 feet will be in the -5 to 0° range, which will support surface highs in the low teens across the north to low 20s in southern New England. Both Saturday night and Sunday night will be very cold, with single digits, on either side of zero, likely across the entire region. Sunday night into Monday morning may be the colder of the nights due to optimal radiational cooling conditions. Lows in the -10s will be possible across the north.
Before the high pressure system takes hold for New England, a breeze will remain in place after the storm. This will drive wind chills below zero for much of New England Sunday morning. Interior northern New England could see feels-like temperatures in the -15 to -25° range.
After this coastal storm and ensuing Arctic blast wrap up, another clipper system may be on the docket for Christmas Eve. Clipper systems have been the dominant winter storm type so far in this young winter season for New England. This clipper is poised to bring some light snow showers to New England during the daylight hours on Christmas Eve. This does not look like a major event and will likely provide light accumulations or festive flakes flying for the holiday.
Below: Current weather map for Tuesday morning (December 24):
Christmas Day/start of Hanukkah currently looks to be in the clear with seasonable temperatures and quiet weather after the clipper system's departure. With that said, there is a spread in how the upper-level pattern sets up and how systems next week will track, so we'll need to watch the trends. Large-scale, impactful storms are not in the picture.
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