Bitterly cold air – particularly by mid-March standards – has settled into the region and is going nowhere fast. Temperatures held in the lower and middle 20s across most of the Cape on Saturday and fell well down into the 10s overnight…and will only climb to the middle 20s once again today. All the while strong winds will persist, creating low wind chill values as we close out the weekend.
Cold air will hang on over the area on Monday, with highs only in the upper 20s and lower 30s – well below the average for this time of year.
While the unseasonable cold is certainly headline-making, all weather-eyes are on a storm system expected to impact the region on Tuesday.
Low pressure will develop off the Southeast US coast on Monday and lift quickly northeastward Monday night into Tuesday, strengthening into a strong nor’easter as it makes the journey northward. The storm will pass near New England Tuesday and Tuesday night and lift away from the area on Wednesday.
The system is likely to bring a variety of weather hazards to the Mid-Atlantic and Southern New England, including heavy snow, strong winds and areas of coastal flooding and beach erosion – in fact, there is high confidence in this forecast, resulting in good lead time for forecasters to get the word out.
That said, there is one area where forecast confidence is low: right here on the Cape.
While the air mass is very cold over the region – and most certainly supportive of snow – the storm is going to wrap milder marine air westward (as these low pressure areas always do) on its northern flank as very strong east and northeast winds develop ahead of it. How far westward the milder air can travel – and thus where snow will transition to rain – will be directly related to the exact evolution of the low pressure center and its track.
It’s clear right now that the Cape and Islands will be right on the edge of the marine influence – but unclear as to whether that air mass overtakes the area or remains just to our south and east.
The closer the approaching system tucks in to the Cape and Nantucket, the better the odds that warmer air will intrude into the region for a longer period of time, resulting in more rain versus snow. Conversely, the further southeast of the area the system tracks, the longer the cold air will hang on and the more snow will fall. Quite literally the difference of tens-of-miles can, and likely will be, the difference between at least 12 inches of snow and just a few inches of snow followed by heavy rain.
With that in mind, it’s very difficult to say just how much snow falls on the Cape and Islands and over extreme Southeast Massachusetts. Precipitation should start out as snow and fall heavily Tuesday morning and quickly accumulate to several inches. From that point, forecast confidence drops notably.
Does strong surface high pressure to our north, combined with a rapidly deepening storm to our south, hold winds in a more northerly than easterly direction and prevent the marine air from penetrating westward? Or… does the strong low pressure system, driven by a very potent upper air environment, simply overcome the anomalous cold and get tugged right up and over Nantucket? Such a scenario would ensure mild air in the lower several thousand feet of the atmosphere pivots into the area.
I will work to fine tune the Tuesday forecast over the next 24 hours and iron out these details…but even now it’s safe to say that a rather high impact storm is expected for the area with some rough conditions for at least part of Tuesday.