It’s not too often that still-falling leaves can be seen on top of snow in the Mid-Atlantic/Northeast US as that would require an early snowfall during the latter part of October or November which is certainly less likely than during the winter season. This week’s abnormally cold and stormy weather pattern across the much of the eastern half of the nation has resulted in some unusual snowfall observations for the month of November. In fact, wintertime snowfall has actually been in a relatively long-term upward trend across the entire Northern Hemisphere with some of the snowiest winters recorded taking place during just the last decade.
The unusually cold and stormy weather pattern of this past week has resulted in some unusual snow observations for the month of November all the way from the Deep South to the Northeast US. Earlier this week, many spots in the southern US recorded their earliest measurable snowfalls ever (e.g., Houston, Texas, Monroe, Louisiana, Arkansas Post, Arkansas). Yesterday’s accumulating snow was centered on the Mid-Atlantic region and Northeast US and it too resulted in some impressive early season snowfall statistics. For example, the 1.4 inches of snow recorded at Reagan National Airport (DCA) in Washington, D.C. was their first measurable November snow accumulation since 1996. The 8.1 inches recorded in Allentown, Pennsylvania (Allentown Lehigh Valley Airport) was the heaviest November snowfall there since records began in 1944 (source EPAWA, twitter). In New York City, the measurement of 6.4 inches at Central Park was the most on any November day in 136 years and the earliest ever for a reading of 6 inches or more. Finally, Penn State University in central Pennsylvania recorded 11.5 inches which was their fourth highest November snowfall ever.
One way to monitor the frequency and intensity of snowstorms in the Northeast US is to use a ranking methodology known as the Northeast Snowfall Impact Scale (NESIS) which was created at NOAA by Paul Kocin and Dr. Louis Uccellini (currently NWS Director). This scale is used to rank high impact Northeast snowstorms and is analogous to the Saffir-Simpson and Fujita scales which are used to categorize hurricanes and tornadoes respectively. The NESIS scale has 5 categories that range from “notable” to “extreme” and factors meteorological measurements and population statistics to provide an indication of a storm’s impact on society. The NESIS scores are a function of the amount of snow, the area affected by the snowstorm and the number of people living in the path of the storm. The aerial distribution of snowfall and population information are combined in an equation that calculates a NESIS score which varies from around one for smaller storms to over 10 for extreme storms.
The latest decade that runs from the winter of 2008/2009 to last winter features far and away the most “NESIS” storms in the Northeast US going back to the 1950’s. In fact, there were 29 impact northeast winter storms in this particular 10-year period and no previous decade had more than ten storms.
In addition, the entire Northern Hemisphere has actually experienced an upward trend in wintertime snowfall going all the back to the 1960’s. In fact, data from the Rutgers Snow Lab shows that some of the snowiest winters ever have taken place in just the past ten years or so. This winter season of 2018-2019 is off to a fast start in terms of Northern Hemisphere snowfall when compared with the last several years - many of which were on the high side normal.
Meteorologist Paul Dorian