Snow: While this storm will be a fairly long duration event – kicking off a bit before midnight (though perhaps preceded by some ocean effect flurries and snow showers today) and likely lingering through the entire day on Thursday and into Thursday night – a lot of the snow from this upcoming weather system is going to fall in a relatively short period of time here on the Cape. Expect several hours of moderate to heavy snow – perhaps 1 to 2 inches per hour – to develop around midnight and to continue into the pre-dawn hours. I wouldn’t rule out a flash of lightning / rumble of thunder as well.
This heavy band of snow is being driven by extreme low and mid-level “frontogenesis” – basically a fancy way of describing, in this case, how a strong push of warm air is punching into an existing cold air mass. Once that region of strong frontogenesis lifts to our north, a lot of the “good” dynamics for heavy precipitation production will weaken and our snow will become lighter. At the same time, warmer air will begin to infiltrate the low and mid levels of the atmosphere and we should see a mix with sleet and rain develop in the pre-dawn hours…with an eventual transition to all sleet and maybe all rain in spots (Outer Cape especially).
This will be the general theme of the day on Thursday (light rain, sleet and snow), until low level cold returns and flips us back over to snow and flurries in the afternoon hours…which will linger thanks to some ocean effect into Friday morning. When all is set and done…snowfall totals should look something like this…with the best bet for picking up greater than 6 inches being on the Mid to Upper Cape.
There are two other concerns with this incoming nor’easter. One is wind (and any associated issues) and the other is coastal flooding.
While this storm won’t pack the punch of our historically big ones, it will certainly have enough to work with to create some strong wind gusts. The combination of a tight pressure gradient and favorable mixing because of the temperature profile will yield a strong northeast wind with gusts over 50 mph likely…perhaps nearing or even topping 60 on parts of the Outer Cape. That, combined with snow that is likely to be rather heavy and wet, is going to lead to some scattered power outages overnight. The wind won’t really calm down much until Thursday afternoon and evening.
Tides are astronomically high thanks to the recent new moon. High tide at Barnstable Harbor Thursday midday (1:03PM) is predicted to be 11.44′ without any surge. At Sesuit Harbor it’s 11.77′. The lengthy period of strong onshore flow will most certainly pile some water up into Cape Cod Bay and should bring a surge of 1 to 2 feet. That, combined with wave action, will be enough to bring some minor coastal flooding and very likely some substantial beach erosion to the vulnerable northern shores inside of Cape Cod Bay. This shouldn’t be a “memorable” coastal flood situation but there will certainly be some impassable roads and inundation of low-lying areas.