Thursday, September 26, 2013

The Cool, Wet Summer of 2013

This past summer (June 1-August 31) was a great relief from the past three scorching summers.  Remember that the summer of 2010 and 2011 were back to back the warmest summers on record.  Last summer wasn’t quite as hot, but we did see the all-time record high temperature for South Carolina broken when it reached 113 F in Columbia.

It was during this time that much of the region was also battling drought.  There was some rainfall during the normal wet season of summer, but there were few wet months beginning in 2010.  In fact there were only 8 wet months out of 36 ending in 2012.  It looked like it would never change.

However, the weather pattern began to change in February of this year.  Rains began to increase, but it also got colder.  There were shifting patterns throughout the spring, but it too was cool and wet.  Then summer began with a very sluggish pattern that dominated June and July.  It was not as dominate in August, but it was still enough to keep the month on the cool side.

This weather pattern persisted for much of June and July.  Click on image for a larger view.  Image Credit: WLTX-TV.

There were no 100 degree-plus days for 2013 which is the first time since 2004.  There is a relationship between wet summers and not seeing 100 degrees.  Eleven summers had no 100 degree temperatures of the 15 wettest summers.  However, only one summer escape 100 degree heat of the 15 driest summers and that was in 1946.

Here is how it shaped up for Columbia, South Carolina this summer:

A look at the summer of 2013 for Columbia, South Carolina.  Click on the image for a larger view.  Image Credit: Climate Central.

Note that is was a slightly cooler summer than normal, but it was the sixth wettest summer on record.  The irony is that the cooler than normal weather did not come from cooler air masses invading the region.  Low temperatures continued to be warmer than normal and averaged 1.1 degrees F above normal.  It came primarily from the wet weather which produced an abundance of clouds.  High temperatures averaged 3.1 degrees F below normal.

Summer nights have trended warmer for South Carolina since about 1970.  For an interactive version on this image click here.  Click on the image for a larger view.  Image Credit: Climate Central.

The trend in warmer summer nights is a trend that has persisted since 1970.  There is considerable variability from year to year, but the trend is unmistakable.  This is consistent with the rise in greenhouse gases which tend to affect nighttime temperatures more than daytime temperatures.

There have been projections of a colder than normal winter ahead.  However, at the beginning of September there were no climatological signals that would indicate what kind of weather to expect this winter.  Thus, it is still an open question.