Textbook storm

As Paul Kocin, who literally wrote the book on snowstorms with Louis Uccellini, wrote a couple days ago in the National Weather Service’s extended forecast discussion, “The mechanisms coming together for a major snowfall are textbook.”

But how have meteorologists been able to be so confident so far in advance that a big snowstorm will happen?

One reason is how far in advance the forecast models locked onto the pattern which will produce the storm.

Model “ensemble spaghetti,” which is one tool that can give an idea of predictability vs. uncertainty, showed much more consistency starting 5–6 days in advance, depicting a deep, strong mid-upper level trough conducive to a large storm, and slow movement resulting a long duration. Plus, the storm is developing over land, not like, say, a hurricane coming from the ocean and angling toward the East Coast in a way such that just a slight swerve could result in a miss.

But what about snow? Well, it’s as easy as A, B, C.

There are two necessary fundamental ingredients.

A

COLD AIR

For this storm, there’ll be a fresh bountiful supply coming in from the north side …

… as an arctic high pressure system arcs around the cyclone.

+B

MOISTURE

Plenty available, coming from both the Gulf of Mexico and the Atlantic Ocean.

=C

SNOW

And a lot of it across a broad swath. That’s what we’re sure of. There are tricky parts of the forecast details such as exactly where a sharp northern edge of the heavy snow sets up, including in the New York City metro area, and also there’ll be ice on the southern fringes of the snow zone.

And…

A couple more things.

A tight pressure gradient between the cyclone (low) and anticyclone (high) will produce strong winds capable of bringing power outages, plus coastal flooding & erosion.

Sea surface temperatures (SSTs) in and near the Gulf Stream are much above average. This is not the cause of the storm, which would be major regardless, but everything else being equal adds a bit extra octane in a couple of ways.

The combination of all of these “textbook” ingredients, along with severe thunderstorms on the warm side of the storm, will create a number of hazards— STAY SAFE!