Science Lessons from a big snowstorm

By Jack Williams ©2015

Like any big weather event the storm that spread snow from Tennessee and North Carolina along the East Coast to New England on December 18-21, 2009 is a good source of real-world science lessons.

With this storm, as with most winter storms, some of the most appropriate lessons revolve around how meteorologists produce forecasts and how people should use weather forecasts.

Since I live in the Washington, D.C., area I had a strong personal interest in both the forecasts and the storm itself.

Jack Williams perpares to begin digging out from the Blzzard of '09 as the snow is still falling. Photo by Darlene Shields.

Jack Williams prepares to begin digging out from the Blizzard of '09 as the snow is still falling. Photo by Darlene Shields.

Following the forecasts and watching the snow fall  made me think of the March 12-15, 1993 “Storm of the Century,” which brought 13 inches of snow to Washington’s National Airport, and much heavier snow to places from the mountains of North Carolina to New England and western New York.

(The 2009 storm brought more snow to Washington, but didn’t affect as large an area or as many people.)

The forecasting chapter of The AMS Weather Book opens with an account of the successful forecasting the  1993 storm in comparison with the failed forecast for the famous Blizzard of 1888.

By the way, the big December 2009 East Coast storm in general did not meet the National Weather Service definition of a blizzard: Winds of 35 mph or faster, low temperatures, and sufficient snow in the air to reduce visibility to less than 0.25 mile, lasting three hours or longer.

For example, at Washington’s National Airport on Dec. 19 the average wind speed for the day was 17 mph with the highest reported speed of 28 mph. Visibility fell to 0.2 and 0.1 miles from 10:20 a.m.  to 2:52 with but wind speeds between 16 and 18 mph.

This information is from the Weather Underground National Airport weather history page for Dec. 19.

The story that opens the forecasting  chapter of the AMS Weather Book is built around the experiences of Louis Uccellini, who at the time headed the National Weather Service division that produced forecasts based primarily on interpretation of all of the available numerical weather prediction models.

(Uccellini is now Director of the NWS National Centers for Environmental Prediction.)

He describes the 1993 forecast as “a seminal moment in the whole forecasting enterprise.”

This is why I used his story to open the forecasting chapter, which has a strong focus on how computer models are the core of today’s weather forecasting.

The “Explorations: The 1888 and 1993 Northeast Storms” page on The AMS Weather Book’s supplemental Web site has links to more detailed information on these two important Northeast snow storms. In addition, this Web site’s “Sources for Chapter 7″  page will help you learn more about several aspects of weather forecasting, including its history.

One of my main sources for Washington forecasts is the Capital Weather Gang on The Washington Post Web site. I like it because those who run the site don’t hype evens, especially snow storms before the odds are at least 30% of the event occurring, as Jason Samenow, the site’s chief meteorologist, wrote on Saturday, Dec. 12.

His comments could help spark a good discussion in a high school or college class, especially in a college course for students who aren’t majoring in meteorology, on the role of television meteorologists as reliable sources of important information who are sometimes under pressure to hype major events.

On Monday, December 21, the Washington Weather Gang published How Did This Happen” — a detailed look at the meteorological background of the storm beginning with the role of global weather patterns, including the Arctic Oscillation and El Niño. Chapter 5 of  the AMS Weather Book explains these and other weather patterns.

A more detailed and technical source of background information on storms like the December 2009 event is Northeast Snowstorms by Paul J. Kocin and Uccellini. It includes both information about the effects of most important storms and the meteorology of the storms.

I conclude Chapter 7 of the AMS Weather Book with a brief discussion of the need for meteorologists to do a better job of communicating their level of confidence in particular forecasts and how to use predictions that are probabilities.

In the book I cite the Capital Weather Gang for giving the forecasters’ confidence in their predictions. For winter storms, the site also gives the probabilities of various amounts of snow.

In the AMS Weather Book I describe a March 2001 East Coast storm forecast that didn’t bring the predicted snow to big cities, but that many television stations had hyped. That prompted a National Research Council workshop on “Communicating Uncertainties in Weather and Climate Information.”

The report of this workshop, which is available as a free PDF download, would be good material for a class discussion on how to use weather forecasts.

In 2006 the National Research Council published an extensive study entitled Completing the Forecast: Characterizing and Communicating Uncertainty for Better Decisions Using Weather and Climate Forecasts. It is available for purchase as a book or as a free PDF download from the National Academies Press Web site.

(Further links will be added to this page when reports other than breaking news stories become available.)

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