It was the best of times, it was the worst of times. Another near blizzard strikes New England, and we’re left to explain the “inconsistencies” in the forecasts. For what it’s worth, the forecast did pan out in some spots (much of Greater Boston), but like the previous two storms, there were lessons to be learned and snow lines to be adjusted.
The clear culprit in the storms: ocean effect snow. Whereby the cold air sweeping in from the ocean gathers moisture, forms clouds and deposits (fluffy, dry “sugar” snow) over land.
(Kinda Dick and Jane, but you get the idea.) This stuff piles up fast, is independent of the storm (key factor here!) and is unrelenting – just ask the folks in Boxford after New Year’s and the folks in Norwell and Duxbury today. What complicates matters is the source for this type of snow: arctic air. It played both accomplice and antagonist in last night’s drama.
Arctic air is inherently dry. It’s thirst for water vapor is what distinguishes it from other airmasses. It robs moisture from your skin, your workplace, your home and, in this case, the ocean. When it interacts with a storm, depending on which direction the wind is blowing, it can dry up advancing snow (last night north & west of Boston) or conspire with the ocean and hammer the coast with ocean effect.
Why couldn’t we see this? See “key factor” above. Two separate snow-producing entities (ocean effect and the actual snow around the storm) are immensely difficult for the models to resolve. They heave, they hiccup, they blur the lines. It’s because of the scale: small for ocean effect, large for storm. We mention the possibility for the heavy snow bands, but we have a hard time pinpointing their EXACT location. Not unlike forecasting thunderstorms in summer. And the sharp cutoff in snow amounts? Overlooked by the models, which like to smear the snow across an area in uniform, graduated amounts. Hardly is that ever the case in real life.
In any event, it’s time to turn the page and face the cold. Weather maps have a great handle on it, and don’t see it letting go for the rest of the month. Prepare for some bone-chilling cold in the next few mornings, with the possibility of a bump up in the numbers by Saturday. That will settle that 12-16+ inches of snow on the South Shore perhaps to a measly 6″ mainly because it’s mostly air and very little moisture.