Low pressure will take shape off the Carolinas on Monday and move northeastward while intensifying Monday night and Tuesday. The storm center will pass east of Cape Cod during the day on Tuesday and then lift into Nova Scotia by midweek. The strengthening nor’easter is expected to give us another round of strong winds and heavy precipitation Monday night into Tuesday, with a sizable snow event possible.
Timing: It looks as though precipitation will overspread the region Monday night and continue – heavy at times – through Tuesday morning before gradually winding down Tuesday afternoon and ending by Tuesday evening. Model guidance is once again pumping out in excess of an inch of precipitation around the area, with some products yielding nearly 2 inches of total precipitation (rain and/or melted snow equivalent) yet again.
Wind: This will be yet another very deep storm system in the western Atlantic, with surface pressures dipping perhaps as low as 970 mb (28.64″) as the system passes by the region Tuesday morning. Thankfully, the core of the resultant northeasterly low level jet is not as strong as the system last week (peaked at close to 95 knots at 925 mb vs 60-70 knots) so we should not see a repeat of the widespread 80-90+ mph gusts we endured in the early March powerhouse storm. Instead, frequent gusts of 45 to 60 mph appear most likely. Winds of this magnitude would cause some localized tree and limb damage, which could be exacerbated by any heavy wet snow that falls (see below).
Snowfall: I’ll work to fine tune the snowfall forecast today and tonight as details of the low level temperature profile and extent of the moisture field become more certain. At the current time, it looks as though the atmosphere will be cold enough to support a mostly snow event across the region, although here on the Cape – and most especially on the Lower and Outer Cape and over the Islands – temperatures in the lowest 1000 feet or so of the atmosphere will be marginal (low and mid 30s) through the first half of the event, before turning colder.
Consequently, precipitation-type is a question for a time. It’s possible that precipitation falls as rain, a back-and-forth mix of rain and snow or just a tough-to-accumulate-wet-snow for the first half of the storm over our area. Unfortunately, this aspect of the forecast comes down to a matter of a couple of degrees. Quite literally a degree or two can make the difference between a sloppy coating of slush and a few inches of heavy wet snow over a matter of an hour or two. Extend that out over a 6 to 12 hour period and you’ve got a wide range of possible snowfall totals. Likewise, some model guidance suggests that precipitation falls as heavy rain and then flashes over to heavy snow about half way through the event.
With that said, I suspect the Mid and Upper Cape stand the best shot of seeing over 6 inches of snow…and if the atmosphere proves cold enough…upwards of a foot of snow would be in reach. Further inland, a solid 6″+ snow event seems likely and if we don’t see guidance tick back eastward some, locations from Boston to Providence could be looking at a foot of snow as well.