Native Plants, Habitat Restoration, and Other Science Snippets from Athens, Georgia

Sunday: 24 November 2013

The Summer Just Past  -  @ 08:20:34
We had a remarkably wet (once in 30 years), somewhat cooler (once in 4-5 years), very humid summer in northeast Georgia.

Here are the usual temperature anomalies, this time for the 3-month period beginning Jun 1, at the National Weather Service Climate Prediction Center. Displayed is the mean temperature anomalies.

Click on the image for the high and low anomaly graphic on a new page:

Much of the eastern US was cooler than average this past summer, especially the central eastern US. Texas and the northeastern US were warmer than usual by just about the same 1-2 degF that the rest of the east was cooler. There were no really sharp gradients in change from place to place.

But the West was warmer to much warmer, by as much as 4 degF in parts of the West. There were unusual sharp gradients, though, in many places, especially in southern California, Arizona, and New Mexico.

The maximum and minimum temperature anomalies (click above figure) show a familiar pattern for much of the US: nighttime lows were warmer while the days were cooler. Often this is due to cloud cover, and certainly that was true for us.

Here is the National Weather Service Climate Prediction Center's anomalous precipitation plot for Jun 1-Aug 31.

West of the Atlantic states and their immediate neighbors, there were numerous areas with around 50-75% rainfall, interspersed with normal to slightly above normal summer precipitation. Central California was more intensely drought stricken, with rainfall amounting to 25% give or take. More abundant rainfall occured throughout the eastern Atlantic states and their immediate neighbors, sometimes up beyond twice normal.

For the Athens, GA area:

Our summer average temperature was 77.2 degF, not quite 2 deg below the long term 78.8 deg average. However, our average high temperatures were 3.1 degF below the usual summer high average of 89.3 degF.

So temperatures in our area were cooler than average, but not by very much. There have been quite a few cooler summers since 1920, somewhere around thirteen, with another dozen or so just about matching our average. So as far as temperature was concerned, ours was about a once in 4-5 years event.

The histogram below shows the breakdown of high and low temperature range counts from the summer of 1948 on. The error bars are just plus/minus one standard deviation, which I arbitrarily set as the limits outside of which are "significantly" anomalous.

The number of really hot days showed a significant decrease by 50% in the 90-100+ degF ranges, with most of those daily highs ending up in the 80-89 degF range. There were no really significant changes in the nighttime lows, though there was a similar trend for a decrease in the number of warmer nights, paralleled by an almost significant increase in the cooler nights.

And so that does bring us to the rain for our area: in short, lots and lots of rain. Official Athens rainfall was 23.08", almost twice as much as the 12.45" Jun 1-Aug 31 normal total. Out here in Wolfskin, we had 26.26".

These totals are greater than any summer since 1920 except for 1967 (27.1") and 1994 (29.4"). This was about a 1 in 30 years surplus rainfall summer.

In this histogram of summer precipitations by summer rainfall totals (1920-present) we are pretty close out there on the right extreme.

It was also, to my mind, a fairly miserable summer. Day after day we had very humid air flowing in from the south or east, with little in the way of cold waves to break up the humidity. With temperatures just somewhat cooler, there was little relief for three months.

Here is a "misery plot," showing the minimum daily humidities during the relevant part of the last three years. I also included a running average, and then colored in the anomalously high humidity days for 2013 in green.

You can see how the green begins just at the end of May, and then continues through August. (The same thing happened to a lesser extent last summer, from August on.) That green represents all those humid days, and I should know! I hiked 110 miles sampling box turtles from June through August, and spent at least 122 hours doing it.

Another way of looking at it is to count the number of points below the 30% humidity line. Between June 1 through August, you'll see no green points (2013), while there will have been plenty of red and blue points (2011, 2012). The usual cutoff for fire weather is 25%, so as you can imagine there were virtually no brushfires this past summer.

State of the Climate

NOAA's State of the Climate product for Summer 2013 is available. It gives a good summary of summer regionally across the US.

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