CNN
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As the United States prepares for a winter heavily influenced by the first strong El Niño Over the years, scientists at the National Oceanic and Atmospheric Administration have published maps that provide insight into where snow might accumulate.
El Niño – a natural model of ocean and weather in the tropical Pacific – is expected to reach the highest level since a very strong El Niño in 2015-2016 favored the the warmest winter on record across the contiguous United States, according to NOAA.
Although no two El Niño winters are the same, the phenomenon generally results in wetter and cooler weather in the southern United States, while the north becomes drier and warmer. And it’s exactly what is expected this winter.
However, wetter weather does not necessarily mean more snow. And when it snows, the amounts can vary greatly from place to place.
This is where the new cards They show where snow is more or less likely during El Niño winters compared to average.
There’s just one caveat: These maps are historical guides, not forecasts, to how snow will develop during the season. A real forecast of snowfall account for a variety of atmospheric and climatological factors, not just El Niño.
“El Niño tips the balance in favor of certain climate outcomes, but never guarantees them,” explained Michelle L’Heureux, one of the two scientists behind the new maps, in a NOAA blog post.
NOAA Climate.gov
Snowfall during all El Niño winters (January-March) compared to the 1991-2020 average (after removing the long-term trend). Blues indicate more snow than average; browns indicate less snow than average.
The map above shows the amount of snow that differs from average during all El Niño winters, regardless of El Niño strength. The drier trend that is typical in the northern United States appears well in beige and brown shades, while the wetter, snowier trend in the southern United States appears in blue shades.
This trend comes from the jet stream shifting south, pushing storms across the southern part of the country at the expense of the north. And an increase in storms in winter means snow is more likely.
The stronger an El Niño phenomenon, the greater its impact. The map below shows the same data for stronger El Niño winters. Pronounced darker hues represent more extreme changes in snowfall during a strong El Niño compared to an average episode.
NOAA Climate.gov
Snowfall during all stronger El Niño winters (January-March) compared to the 1991-2020 average (after removing the long-term trend). Blues indicate more snow than average; browns indicate less snow than average.
The big snow winners are the Mid-Atlantic, the higher elevations of the Southwest and California, and the South, although with one important caveat.
It still has to be cold for snow, so the chances don’t vary as much from normal in parts of Texas and the Southeast, which tend to stay too warm for the flakes to fly.
The jet stream effect of El Niño is especially noticeable in the higher areas of the West, where cold and snow are generally not difficult to find. The mountains of the Southwest and California thrive while the Northwest is absent due to fewer storms.
Storms that affect snow chances in the mid-Atlantic typically take a path along the spine of the Appalachians or move away from the coast and become northeast storms.
These northeast winds can be “boosted” by abundant tropical moisture during El Niño and cause “two to three large snowstorms” on average, according to Jon Gottschalck, chief of the Climate Prediction Center’s operational forecasting branch from NOAA.
That could lead to above-average snowfall in places like Washington, D.C. and Baltimore, where less than an inch fell last winter.
Although the Northeast typically lacks snow during a strong El Niño winter, it only takes one massive storm, like a “strengthened” Nor’easter, to skew snow totals for the entire season.
Snow lovers in the Northwest and Midwest will also have to join their counterparts in the Northeast in hoping for a big storm. Stronger El Niño events have caused less snow than average in the past.
NOAA Climate.gov
The number of years with below-average snowfall during the 13 moderate to strong El Niño winters (January-March average) since 1959. Red indicates locations where more than half of the years had snowfall snow below average; gray shows locations where below-average snowfall occurred in less than half of the years studied.
Removing snowfall totals from the map and focusing on the number of stronger El Niños with below-average snowfall helps identify outlier storms.
In the map above, darker reds indicate areas that experienced more years of below-average snowfall during moderate to strong El Niño winters.
Parts of the typically snowy Midwest and Northeast that also suffer from snowfall deficits stand out clearly, a sign that may be where El Niño steals the most snow, most often.