Weather's Ups & Downs

It has been like a roller coaster for temperatures since late October beginning with a freeze on the 26^th Columbia, SC, when the temperature dropped to 30°F.  This came after an exceptionally warm fall.  Here is a look at the ups and downs since October 26^th:

Month	Date	Temp
Oct	26	30°
	30	82°
Nov	4	38°
	6	77°
	9	32°
	10	72°
	14	23°	New Record Low
	18	85°	New Record High; Trace of Snow Evening
	19	38°
	22	76°
	25	22°
	26	71°
	28	23°
Dec	6	82°	Record High Tied
	13	25°
	21	81°	New Record High

The forecast for the 22^nd of December is for record high temperatures with much colder weather returning for Christmas Day.  Thus the roller coaster will continue for a while.

What is causing this?

A recent conversation with Mike Halpert, the Deputy Director of NOAA’s Climate Prediction Center, pointed to few short-term climate signals that would suggest the kind of weather we have been seeing.  In fact most of the signals indicate that we should be seeing warmer than normal weather.  This has been true in Columbia, SC with a December average temperature of 3.8° F above normal through the 20^th.  However, November averaged 2.1° F below normal.

It turns out that a weather pattern in the eastern Pacific has been influencing much of the weather since late October.  A ridge of high pressure has been persistent just off the west coast of the U.S.  When the ridge is in place it helps drive cold arctic air into the nation’s mid-section and when the ridge weakens a more zonal pattern results in moderates temperatures across the country with above normal temperatures in the Southeast.

The 500mb weather pattern for 12z on December 9, 2013.  Northwest winds aloft over the western part of North America were bringing cold Arctic air south.  Click on the image for a larger view.  Image Credit: WSI.

A strong ridge was in place off the West coast on the morning of December 9^th.  Some of the coldest air of the season was spilling into the U.S.  Much of the western and central U.S. was in a deep freeze.

Morning low temperature reading for December 9, 2013.  Click on the image for a larger view.  Image Credit: NOAA/NWS.

This pattern of ups and downs puts stress on the body and often leads to a rise in sickness especially colds and flu.  It may be nice to get out when it is warm, but we do pay a price for the extremes of temperature.  A more even temperature regime whether cold or warm would help, but that has not been the pattern this year.

If this pattern continues through the remainder of the winter, then we may yet see a warmer than normal winter.  However, we may also see more severe storms as the collision of extreme air masses leads to more active weather systems.  A more active winter tornado season in the South, like last winter, is certainly a possibility.