Bitter Cold Blasts Northeast

While parts of the East are suffering from yet another deep freeze, the exact opposite is true for the other half of the country: much of the West is on track for one of its mildest winters on record.

Out of the 365 sites monitored by the Midwestern Regional Climate Center, nearly 30 have experienced their mildest winter so far on record according to their Accumulated Winter Season Severity Index (AWSSI).

The AWSSI is based on temperatures and snowfall for the entire winter season to date, and a lower score means milder temperatures and less snow. So for the cities that are making a run at the most mild winter on record like Salt Lake City, Albuquerque and Reno, Nevada, that means warmer temperatures and less snowfall.

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This is just a continuation of a trend that started with the beginning of meteorological winter in December - nine states across the West had their warmest December on record, according to a report by the National Centers for Environmental Information.

Lack Of Winter Is A Potential Long-Term Problem

The snowpack is also suffering across the West’s mountains.

Watershed basins from the Four Corners region to the Pacific Northwest have less than half of their typical snow water equivalent (SWE), which is a measure of snowpack, for this time of year. There are also numerous monitoring stations across the basins that have their lowest snowpack on record for late January.

Take this Colorado snow water equivalent map below from the Colorado Snow Survey Products. As you can see, it is the worst snowpack for Colorado on record.

The California snowpack is running about 57% of normal, as of February 1, according to the California Department of Water Resources.

But this is a bigger problem than just disappointment over a lack of winter weather and opportunities for outdoor winter sports.

The West relies heavily on the mountain snowpack that builds up over the winter as a source of water throughout the year which is steadily released into rivers and reservoirs as temperatures climb in spring and summer.

That means that a weak snowpack at the end of winter can cause long-term problems for the West due to a lack of water.

SWE values typically peak across watershed basins in the West in early to mid spring, so there is still time for the snowpack to increase, but conditions are already set for struggles with drought conditions for the warmer months.

What’s Going On?

Take a look at that AWSSI map again. Notice anything?

While the West is wondering where winter has gone, parts of the eastern half of the country have had an overabundance of it, especially in the Great Lakes and the Lower Mississippi Valley.

A ridge of high pressure has dominated the western half of the country, allowing for consistent warmer weather to prevail as well as causing the jet stream to steer storms further north, limiting snowfall for the mountains.

This trend is associated with the negative phase of the Arctic Oscillation (AO), a global circulation pattern in our atmosphere that indicates the strength of the polar vortex. When the AO is in a negative phase, the polar vortex is weaker, which allows for colder air to spill into the eastern half of the country while trapping the western half under warmer conditions.

Sara Tonks is a content meteorologist with weather.com and has a bachelor’s and a master’s degree from Georgia Tech in Earth and Atmospheric Sciences along with a master’s degree from Unity Environmental University in Marine Science.