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The polar vortex returns

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If you liked the polar vortex earlier this month, then you’ll definitely like its return this week. Although the polar won’t be quite as far south or quite as cold, it will still make its presence felt. By the way, the only thing of consequence about the “polar vortex” is that the media has discovered it. Meteorologists have known about its existence and characteristics for decades.

Unseasonably cold (sometimes sub-zero) temperature readings (even during the day) will affect large areas from the northern Plains to the Northeast and as far south as the Ohio Valley. Further to the south (e.g., Georgia, Alabama, and the Carolinas), warm weather early in the week will yield to much colder temperatures by midweek. For northern parts of the Gulf Coast states, look for readings only into the upper teens and lower twenties on some nights and upper thirties to lower forties by day.

Linked to the polar vortex will be a series of smaller weather systems, known as “clippers.” Typically originating in the area near Alberta, Canada, these small-scale features move southeastward along the western flanks of the upper-level polar vortex or eastern U.S. trough. A trough is u-shaped wind flow pattern in the northern hemisphere. It is easy to see the polar vortex (red L), the upper-level trough and the smaller scale features (brown lines) pin wheeling around it in a counter-clockwise spiral.

As each of the smaller-scale features advances to the southeast, it may bring a burst of snow with it (usually light), followed by a reinforcing blast of arctic or polar air. Once the feature reaches the warmer waters off the U.S. East Coast, it is not uncommon for the system to generate a significant coastal/ocean storm.

Right now, it appears that this cold weather pattern has about a week to go before it breaks down and allows weather systems to progress across the Nation.

While regions to the east of the Rockies are locked in a cold pattern, places to the west of the Rockies are in the throes of a very warm weather pattern and an associated, prolonged drought. An upper level ridge (shaped like an upside down “U,” helps to steer storms to the north of the region. It also leads to strong subsidence events with associated well-above temperatures and Santa Ana winds (much like what occurred in northern California in late November 2013).

Many places in the west are far below average in rainfall and/or snowfall. With snowpack at historic (within recorded history) lows, the governor of California proclaimed a state of emergency this past week due to the current and expected persistence of drought conditions.

© 2014 H. Michael Mogil

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