Rick Atterberry, EDEN Immediate Past Chair, writes about the weather.
The east coast blizzard that started Monday evening, January 26 and continued in some places into the early morning hours of Wednesday, January 28 provides us an opportunity to discuss a couple of related items.
What is a blizzard? Contrary to popular perception, the official definition of a blizzard has more to do with the wind and visibility than an exceptional amount of snow. According to NOAA, a Blizzard Warning is issued when the following conditions are expected over a minimum three hour period:
- Sustained winds or frequent gusts of 35 miles an hour or more along with considerable snow or blowing snow.
- Visibility of ¼ mile or less in snow or blowing snow.
People in many parts of the country are familiar with a concept called a “ground blizzard.” That occurs after a recent snowfall has ended but when the wind picks up and the snow begins to blow around to the point that visibility is restricted. This blowing snow often causes as much traffic danger as the original snowfall. In a ground blizzard you may actually be able to look straight up and see the sun while visibility in front of you is a near white-out.
Why was the specific forecast for New York City so wrong? Well, it was and it wasn’t. Veteran forecasters will tell you that winter weather, particularly snowfall amounts, is very difficult to forecast. Specifically in this week’s scenario, the storm tracked farther east than had been anticipated moving NYC out of the heaviest snow. Although it should be pointed out that snow amounts reported in the boroughs ranged from almost 9 inches to about a foot, not an insignificant snowfall. Out on Long Island, the weather did play out as forecast as it did to the north through Connecticut, Rhode Island, Massachusetts, New Hampshire and Maine. Snowfall in excess of two feet was common.
One way to look at the difficulty of forecasting snowfall amounts is to consider a typical summer storm system. Do you really notice much of a difference between a half-inch and an inch and a half of rainfall? Unless it falls all at once, probably not. Now, using the common moisture ratio of 10:1 that would mean a snowfall range of between 5 and 15 inches! Most of us would find that an important distinction. So, being able to accurately determine how much moisture is available in a particular location and the actual ratio, which varies widely, are key to nailing a snowfall forecast. Add in the fact that this storm was pulling moisture from the open ocean waters and other variables such as “banding,” where heavy snow sets up in rather narrow bands, and you can understand the difficulties forecasters face.
This week’s storm had many of the characteristics of a classic Nor’easter. Heavy snow, high winds and coastal flooding. In fact, from early news reports, it is probable that most of the damage from this storm is the result flooding of homes, businesses and infrastructure. Wind gusts of 70+ miles per hour were reported , including a few of hurricane strength. At times, the monster waves created by this storm hit at high tide, greatly increasing the possibility of damage.
So the “Blizzard of 2015” had dangerous elements beyond just the snowfall…high winds, flooding, falling trees, etc. Were the warnings overdone? (I almost said overblown but that would be a very bad pun, indeed.) I don’t think so. People prepared. They stayed off the roads which makes snow removal MUCH easier. Deaths and injuries were few. In short, the warning system achieved its intended goals, protection of life and property. I won’t quibble about precise snowfall amounts. But if you’re interested, check out the New York NWS and Boston NWS reports of storm totals and maximum wind speeds.