A large Nor’easter or coastal storm can make or break the ski season on the East Coast. They often produce heavy snow of 1-4ft and can be major contributors to the snowpack from the Mid-Atlantic to New England. These storm systems are powerful and unique to this part of the United States. Here I will cover the basics of how Nor’easters form, what type of weather they bring, and what that means for your skiing and riding.
Nor’easters get their name from the cold and strong northeast winds that often accompany heavy snow. Whether you are from the southern Mid-Atlantic or New England, where they call them Nor’eastah’s, these storms can bring heavy snow and blizzard conditions to a large area of the East Coast. They can also bring heavy rain and mixed precipitation, which can ruin a ski and ride season.
Nor’easters are often called ‘Coastal Storms’ by forecasters at OpenSnow and elsewhere in the weather world. Both names mean the same type of weather system - a powerful storm for the East Coast. I will use Nor’easter for the remainder of this article, but just know coastal storms have the same properties.
Not all storms along the East Coast are Nor’easters. What makes a Nor’easter is the comma-shaped cyclone head (image below), which characterizes a strong storm system, that brings the famous northeast winds.
NASA Earth Observatory images by Joshua Stevens, using MODIS data. January 4th, 2018.
How they form
Nor’easters form from a combination of a strong jet stream, cold air, and moisture in the atmosphere. All Nor’easters develop from a storm moving across some portion of the US or Canada. They move across the country and follow the track of the jet stream, which can bring them to the East Coast.
The angle and strength of the jet stream are very important. The jet stream needs to have a portion of it pointing north, which allows the storm to follow it up the East Coast and it allows cold air to move south. The jet stream needs to have strong winds, which allows the storm to strengthen.
The storm system will gain strength due to the jet stream and a temperature gradient (warm to the south and cold to the north). A strong south-to-north temperature gradient is called a baroclinic zone, which helps Nor’easters rapidly strengthen.
Once the storm system starts strengthening along the East Coast, it becomes a ‘Nor’easter’, and will further strengthen. Sometimes it becomes the famous ‘bomb cyclone’, where it undergoes bombogenesis where the storm drops its central pressure of 24 millibars in 24 hours. This means the storm is rapidly strengthening, which usually means very heavy snow is in the forecast.
Textbook Nor’easter examples from 1/30/1996 and 1/20/1978. Figures from Kocin and Uccellini 2004, “Northeast Snowstorms Volume I: Overview”.
A Nor’easter moves to the north or northeast and can take various tracks that bring it inland, along the coast, or off the coast. The jet stream helps steer the Nor’easter, and depending on its exact track, it will bring various types of precipitation and either weaken or strengthen further.
There are many tracks that Nor’easters take and they can be grouped into two categories. There are the Atlantic coast tracks and the coastal redevelopment tracks. The Atlantic tracks are usually associated with stronger storms that have more moisture with them and often produce more snow due to colder air to the north. The redevelopment tracks cause storms to move in many directions and are more likely to produce mixed precipitation.
Coastal storm track favorable for Nor’easters. Figure from Kocin and Uccellini 2004, “Northeast Snowstorms Volume I: Overview”.
Inland, redevelopment storm track favorable for Nor’easters. Figure from Kocin and Uccellini 2004, “Northeast Snowstorms Volume I: Overview”.
Types of Weather
From snow, sleet, freezing rain, to rain, Nor’easters bring the whole kitchen sink to the East Coast. Due to the temperature gradient that helps Nor’easters develop, temperatures during these storms can range from the 70s to the 10s or even lower. Different quadrants of Nor’easters will have different zones of temperatures and winds due to fronts.
MODIS satellite image from January 4th, 2018. Rough approximations of fronts and areas of precipitation.
The best area to be for snow lovers is the northwest quadrant where the heaviest snow bands develop. Snow can fall at rates of 1-4 inches per hour. Other areas on the western side of the storm can see snow as well but it will not be as heavy as in the northwest areas. Areas on the eastern side of the storm are most likely to see mixed precipitation and or rain.
The eastern areas see warmer temperatures because of the warm front. The warm front brings warm air over cold air, which causes sleet and/or freezing rain. To the south of the warm front, rain will likely fall. The fronts in a Nor’easter affect precipitation type and intensity, which makes the track very important for snow accumulations. It is common for 10-30 miles to determine the difference between several feet of snow or rain.
There is always a dry area of a Nor’easter, which is typically in the southeastern quadrant. This area sees the warmest temperatures and is not where you want to be if you are a snow lover. Fortunately, this area is usually along the coast or over the ocean.
Finally, Nor’easters often bring very cold air behind them and can cause additional snow via lake effect snow around the Great Lakes. This can add even more snow to these areas if the weather pattern is favorable.
Radar imagery from 12 am to 3 pm on December 19th, 2020. This Nor’easter brought over 40 inches to the Binghamton, NY area and 2-3 feet in other parts of NY, MA, ME, NH, and VT.
What this means on the slopes
Nor’easters are usually a great sign for ski resorts and can make a season epic. Unfortunately, not all Nor’easters bring snow, and sometimes they can bring rain, or pass by waving hello with no precipitation at all.
The northwest quadrant of a Nor’easter sees the heaviest snow and is best for the slopes. Depending on the track of the storm, heavy snow can turn to mixed precipitation due to the warm front. The last forecast before a Nor’easter is key to finding the best areas for skiing and riding. A matter of miles can mean an epic day on the slopes and a snowpack that could last through the season.
Snow ratios can vary a lot depending on the physics involved with Nor’easters. Again, the northwest quadrant will have the highest ratios due to cold weather and favorable snowflake development. Other areas will see lower ratios and the surface temperature will have a major impact on how powdery the snow is.
Photo by OpenSnow meteorologist Luke Stone from March 14th, 2014 at Smugglers Notch, Vermont.
Keep tabs on the forecast for any coastal storm or Nor’easter. Forecasters can usually see signs of one coming about a week in advance. As always, the key to any good ski trip is planning several days in advance to make sure you and the forecaster know where the snow will fall.
Zach Butler, Meteorologist for the Mid-Atlantic Daily Snow.