Northeast Snowfall Trends
By David Kroodsma, Climate Central
The past two winters have been extraordinarily snowy in parts of the Northeast and Mid-Atlantic. But exactly how snowy has it been? And how much snow can the region expect in future decades if the climate continues to warm?
You can use the graphics below to find out. The first is an interactive map with weather stations represented by snowflakes. Click on one to see the total winter snowfall for that location for each of the past 31 years. The average yearly snowfall during the past three decades at each location is shown by the gray line, and projected average annual snowfall at the end of the century by the red. (See the caveats on this calculation further down in this post).
|Link to Source Spreadsheet: Source Data|
The second graphic shows the same data in a different format: each row represents the winter snowfall for three decades at each of the 98 weather stations on the map. On the color scale, yellow represents a below-average year and dark blue represents a year with heavy snowfall. The far right column is what climate models suggest an average year may look like by the end of this century. You’ll see that, for each station included in this analysis, the least snowy year over the past three decades is projected to be a typical year in the future.
Keep in mind that the end of the century data consists only of projections, and model simulations of regional snowfall have significant uncertainties.
These data have been provided by the Northeast Regional Climate Center. The weather stations on the map represent a small percent of the weather stations in the Northeast. That’s because many stations were missing data for some years, so we show only those that had nearly continuous snowfall information. Even the stations on the above map were missing up to two years of data, we used data from nearby stations to fill in the missing years. You can see data from all 1,816 weather stations in this Excel file.
How Snowy was the 2010-2011 Winter?
It was a year of heavy snow, but not a record-setter in most locations. Our data includes snowfall through only the beginning of March—so more records may still be set—but just three of the 98 stations analyzed here indicate that the winter of 2010-11 was the snowiest year of the past three decades. By comparison, during the winter of 2009-2010, 13 locations, mostly in the mid-Atlantic, set records for the heaviest total winter snowfall.
Total winter snowfall for 98 locations in the Northeast and Mid-Atlantic during the past 31 years. each row represents the winter snowfall for three decades at each of the 98 weather stations on the map. On the color scale, yellow represents a below-average year and dark blue represents a year with heavy snowfall. The far right column is what climate models suggest an average year may look like by the end of this century. For each station included in this analysis, the least snowy year over the past three decades is projected to be a typical year in the future.
For most locations, it would take another month of heavy snowfall to come even close to the 1995-96 winter, when almost half of the above stations set records. On the graphic above, that winter looks almost like a dark blue vertical line – which indicates that the heavy snowfall was widespread across the region. That winter featured the Blizzard of ’96, which dropped as much as four feet snow in some spots in early January, and was followed less than a week later by another large snowstorm.
The color grid above shows that one winter may be particularly bad in one part of the Northeast and Mid-Atlantic, but only average in another. Last year for example, the Mid-Atlantic endured record snows, but parts of New York and northern New England had a below-average year. Headlines are often skewed toward population centers: if it’s snowy in New York City but not elsewhere, people might get the false impression that it’s been a record year for snow.
Is Climate Change Making Snowstorms Worse?
The short answer is “maybe.” Average seasonal snowfall can come from many small storms or fewer, bigger ones. The past two winters have seen an abnormally high number of major storms — storms that drop more than 10 inches over large areas. Both 2009-2010 and 2010-2011 had three winter storms that qualified as at least a “Category 3” based on the Northeast Snowfall Impact Scale (NESIS). Even the 1995-96 winter didn’t have that many storms of this ranking, and you’d have to go back to 1960-61 to find as many high-scoring winter storms in a single season as we saw in each of the past two years.
However, it should be noted that the NESIS scale also factors in whether the storm struck populated areas, so large storms that hit unpopulated northern New England would not register at the upper echelon of this scale.
In the short run, climate change could actually mean more heavy snowstorms. A warmer atmosphere means that the air can hold more water vapor, and this can result in more storms with heavy precipitation. In fact, scientists have already documented an increase in heavy precipitation events. If it is cold enough to snow, these storms can drop heavy snow instead of rain. However, the possible links between climate change and heavy snowfall is an area of active scientific research, with no definitive answers yet. And many credit the past two years of heavy snow to the North Atlantic Oscillation, and not necessarily to climate change.
The Long Run: Less Snow
Evenif heavy snows increase over the next few decades, many climate scientists say that a warmer climate will eventually mean less total snowfall for the northeastern states, as more precipitation falls as rain.
That pattern probably won’t be true in other cold regions. Siberia, Alaska and Northern Canada may experience more snowfall even if temperatures increase. That’s because these places are so cold in winter that even with a ten-degree warming, average temperatures will still be below freezing.
The Technical Details
The estimates of future snowfall represent a simple modeling analysis. Climate models predict that snowfall will decrease in the Northeast and Mid-Atlantic, but they don’t all agree by how much, so we averaged the results of 19 climate models to estimate the expected change in snowfall (we got the climate model output from the WCRP CMIP3 Multi-Model Dataset Archive at PCMDI. We calculated the average change in snowfall between the beginning and the end of the century for each climate model, and got a percent change for each model. We then averaged these percent changes, to get a “best guess” for how much snowfall will decrease later this century.
The climate models, though, don’t produce the same type of output as the “total snowfall” measured at the weather stations on the map. What the climate models measure is the amount of water that falls as snow in a given place. Because wet snow is denser than dry snow, the amount of water that falls as snow doesn’t always exactly correlate with the inches of snow on the ground. We assumed that it did correlate, and we simply subtracted the percentage change in snowfall predicted by climate models from the average winter snowfall over the past three decades for each station. Because warmer snow is wetter and packs more densely, we might have underestimated the change; the warmer snows of the future might bring even fewer inches of snow.
The climate model data are available for numerous different “scenarios” that make different assumptions about how much carbon dioxide and other pollutants humanity will add to the atmosphere. We chose output for a scenario called “A2.” This scenario assumes that humans will continue to use fossil fuels almost unabated, and climate models predict that the earth will warm, on average, between 3.6 and 9.7°F this century, with 6.1°F being the “best guess.”
This scenario seems reasonable given recent emissions and climate trends. Several analyses have shown that if nations limit emissions by the amount they pledged as part of the Copenhagen Accord, the Earth could still warm by more than three degrees Celsius, which is only slightly less than what the A2 scenario predicts.
Here’s another caveat: Climate models are relatively good at projecting temperature change, but they are less skilled at accurately projecting changes in precipitation. And predicting snowfall is especially tricky, as it requires getting both temperature and precipitation details right. As a result, our findings—that seasonal snowfall will decrease between 30 and 60 percent in the Northeast and Mid-Atlantic states by the end of the century—should be taken with a grain of salt.
Of course, scientists have already documented the effects of climate change in the Northeast. Since 1970, the region has warmed by about two degrees Fahrenheit, and winter temperatures have increased even more. One study found that, using a fifty-year data set, almost all weather stations in Maine had already reported a decrease in the winter snowpack. Projecting into the future, the same study estimated that winter temperatures in the Northeast could warm, on average, about 6.5°F this century (using the same A2 scenario), and that the first frost in autumn will come 20 days later. A report on how these changes will affect the economy and society in the Northeast can be found here.