polar vortex weather forecast

 

'Polar Vortex' event could bring extreme cold to the U.S. How that affects the forecast in NorCal

This pattern could hold through the first half of January.

While this polar vortex event will not affect Northern California, its presence in the central and eastern U.S. will have an impact on the weather pattern for the West Coast.

What is the polar vortex?

The polar vortex is a strong band of winds in the stratosphere that loosely trace the Arctic Circle in the Northern Hemisphere. This feature exists year-round.

The polar vortex is a band of strong stratospheric winds that loosely trace the Arctic Circle

When the polar vortex is strong and stable, bitter cold air stays trapped in the high latitudes.

As winter weather patterns evolve, the winds of the polar vortex change in strength. This can lead to a weakening of the polar vortex pattern.

                       When the polar vortex weakens, arctic air can plunge into the lower latitudes.

That weakening allows pieces of the polar vortex to plunge south and bring intense cold to the United States and other mid-latitude places in the Northern Hemisphere. Weather forecast models show this process beginning at the start of January.

What does this mean for NorCal?

Think of the U.S. temperature pattern during the first half of January as a see-saw. While arctic cold plunges into the central and eastern parts of the country, warmer air will rise to balance things out in much of the West.

Polar vortex patterns can be stubborn and linger longer than a typical cold snap. This means that while January will start off brutally cold with rounds of snow in the East, the West could see a long stretch of mild, dry weather.

The latest outlook from the National Weather Service shows a high probability of drier than average weather through mid-January across California, Oregon and Nevada.

This outlook from the National Weather Service shows that a dry weather pattern is likely to develop for much of the West in early January. 

As of Dec. 30, Sacramento and areas north have seen above-average rainfall so far this water year. The snowpack is right at average for the Central Sierra, including the Lake Tahoe region. The North Sierra has a well above average snowpack water content at 166% of normal. The snowpack in the South Sierra is below average at 79% of normal for the date.

The snowpack typically peaks in late March or early April. Spring snowmelt typically accounts for a third of California's drinking water during the summer and fall months.