Jay Gallé: We're riding the temperature roller coaster

Published On: Jan 16 2014 10:11:54 AM CST   Updated On: Jan 16 2014 10:14:51 AM CST

Last week’s cold snap was so cold a few record low temperatures were broken in southeast Louisiana and parts of southern Mississippi. Then, before we knew it, we were back into the mid-70s by Saturday afternoon. That’s almost a 40-degree change over the course of four days.  And that’s the way it works in the wintertime along the Gulf Coast.

As soon as a blast of cold, arctic air descends upon the lower Mississippi river valley, winds shift and we warm up to near record high levels a few days later.  It’s as if we’re on the Zephyr, the popular roller coaster at the old amusement park, Pontchartrain Beach that used to be on a stretch of beach along Lake Pontchartrain at the northern end of Elysian Fields Avenue.

Watch: Today's forecast

Ironically, “zephyr” is an appropriate metaphor since it is a weather term referring to a type of wind.  But it is really only aptly applied when comparing the up and down motion of a roller coaster to that of our temperature regime in winter, because a zephyr is actually a gentle west wind.  The winds that bring cold air are not from the west (but can have a westerly component), and are anything but gentle. 

Gallery: Things freezing on u local

As the fast ribbon of air in the upper levels to our north, known as the jet stream, buckles, cold air from Canada and the polar region is sent southward on brisk northerly winds that ride down the back side of large low pressure troughs that can sometimes span the entire country.  Because of pressure differences created by contrasting temperatures, i.e. cold air from the north invading warmer air to the south, wind speeds can accelerate up to 25 or 30 mph, making the already cold air feel colder.

As we all know, these cold snaps are just that -- snaps.  It’s usually a quick and brief cold air invasion into a region where the average morning low in winter is 45, and the average daytime is high 65.  Last Tuesday we had a high of 36, after a low of 24!

Gallery: Freezing point of household items

The jet stream as buckled again and cold air is heading our way on the heels of little upper air disturbances known as “shortwaves” or “vorticity maxima."  They are the little swirls rotating around the big dip in the jet stream that you sometimes see on television if your eyes haven’t glazed over trying to understand a moving satellite image. These little impulses will drag frigid air from the polar region down to the Gulf keeping the area unseasonable cool with morning lows 3 -- 12 degrees below average, and daytime highs as much as 11 degrees cooler than normal depending on which day of the extended forecast you’re looking at.

So, buckle up and bundle up because we’re about to drop into one of those big dips on the temperature roller coaster!  If you don’t like the cold air, rest assured, we’ll be warming up before you know it -- or, just think ... August.



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