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

Sunday: 4 August 2013

The Month of July  -  @ 14:01:48
It's The Month of July, Number 90 in a series. Rainy conditions beginning in June accelerated in July, and a cool summer continued for us in the southeast.

Here are the usual temperature anomalies products, at the National Weather Service Climate Prediction Center. Displayed is the high and low temperature anomalies.

Much of the eastern US went from weakly warmer than usual in June to considerably cooler in July. In the West, temperatures were considerably warmer for the Pacific Northwest, and cooler for AZ and NM eastward. The northeast had warmer than usual weather in July.

Notice how the days have a deeper cool anomaly in the east, than the nights do. Cloud cover, rain, and high humidity kept us cooler during the day, but prevented cooling at night.

The most common explanation for this summer's unusual topsy turvy weather in the eastern US invokes the Bermuda (aka Azores) High pressure system off the east coast. Normally we in the southeast are covered by this throughout much of the summer, with dry and hot conditions resulting. With the system moving northward, the northeast US has received that weather, and we've had a constant flow of high humidity from both the Gulf of Mexico and the Atlantic Ocean. Cold fronts and diurnal heating have combined to produce an unusual amount of rainfall for us.

We find the National Weather Service Climate Prediction Center's precipitation plots here.

In June, very dry conditions spread northward and westward in the Southwest US. The direction of drought continued toward the Northwest, and became very dry in OR and WA. Rain did spill westward though, into the previously dry southwest. TX, OK, and KS received at least normal rainfall and a surplus in many parts of the states.

The Southeast had a surplus of rain in June, and that continued in an augmented fashion in July. Many locations in NC and GA had up to half their normal annual rainfall in June and July alone.

For the Athens, GA area:

It seems appropriate this month to put up this occasional feature - a combined temperature and rainfall plot for Wolfskin. You can click on it for a larger version in a new window, but the features are pretty clear here.

The blue line is a 25-point running average of temperatures here, so it spans 3-4 days for each average. We were above and below the smooth maroon average since late April, but beginning in June began to dip below that average curve. We've now been below average in July.

The dark green bars represent daily rainfalls in inches, and the lighter green curve above shows the enormous amount of rainfall we've had over the last two months. The dotted line is average rainfall accumulation.

Below is what I've finally come up with as a daily rain/temperature plot. The spiky lines are temperatures recorded during the days, and the lighter blue bars are Wolfskin rainfall measurements.

The black line is the normal average temperature, and you can see that we're now on the downside of summer.

One outstanding feature is the number of times, seven, that we had an inch of rain or more during a daily period. Overall this year, so far, we've had 19 such events, and that's an unusually high number of 1+" rainfalls.

The average monthly temperature for July was 77.8 degF, significantly below the 30-year average of 80.7F. Again, our average high was lower than usual, and our average low was higher than usual.

So it should come as no surprise that we had, again, 0 day more than 1 standard deviation above normal highs (5.2 normal). We had 3 nights with temperatures more than 1 standard deviation below normal lows (4.4 normal).

The monthly histogram below shows the breakdown of high and low temperature range counts from July 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.

As in June, we have significant deviations from the red bar averages, if you accept the 1 standard deviation bars as the threshhold. As already mentioned, we had very few 90-deg , and they ended up as significant additions of 80s days, 27 such, and significantly higher than the usual 14.

The right side of the figure above shows the same thing: more nights in the 60s, and fewer in the 70s, but deviations greater than one standard.

The figure below shows the Athens precipitation data which are official for our area. As usual the green line shows our actual rainfall, the red shows the average accumulation expected. The black dots are rainfall over the last 22 years, and the river of peach shows the standard deviation.

For the second month in a row, we had the welcome blue of surplus rain, greater than one standard deviation, for most of the month. The green line is Athens official, ending up at 9.19" for July. But here in Wolfskin, 15 miles away, we ended up at 13.20"!

Here are the remarkable stats:

Our total rainfall in June and Jully out here was 20.40", not quite half our usual rain for the year. It was the fifth rainiest July in Athens since 1920, but our 13.20" here exceeded any July since 1920. Overall, we have stayed above average rainfall all year since mid-February.

Finally, here is my cumulative rainfall plot. The blue line shows the difference in expected and actual accumulated precipitation since 2005. We've been in a deficit since Jan 2007, with a 2.5 year drought beginning then. There was some recovery in the latter half of 2009, a year of normal rainfall, and then back to drought conditions through last year.

This year we've gone from nearly 30" below the long term deficit to a recovery of 10" deficit. Of course much of that was runoff, but a great deal did soak into the ground here, at least.

Prognosticator stuff:

What is the neat prognosticator telling us? For us here in the southeast, it has been accurate over the last two months for temperature and precipitation. As of 3 Aug, it tells us that we can expect higher than normal precipitation over the next three months. Temperatures should be above normal for the next couple of weeks, then normal thereafter.

Temperatures will become increasingly above normal in the western US over the next three months. Precipitation is above normal in some places over the next couple of weeks, but otherwise normal over the next rhee months.

ENSO stuff:

The folks at CPC have a version of PDF or HTML that is much different from their previous presentations, but at least it's there and the link isn't broken.

As of Jul 29, ENSO neutral conditions continue, and are expected to remain neutral throughout the Northern Hemisphere fall. We've remained ENSO neutral now for over a year. The last such lengthy period was 10 years ago, 2003-2004. You can't use an El Niño or La Niña to explain extreme weather this year.

NOAA's Monthly State of the Climate product for June is available. And last year's annual report for 2012 regionally, nationally, and globally is also available.

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