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

Saturday: 4 January 2014

The Month of December  -  @ 14:20:28
Cold temperatures are moving in, as January progresses. We expect low temperatures here to fall into the single digits on Monday night. This is not something that we have seen in many years. But first!

It's The Month of December, Number 95 in a series. For us in northeast Georgia, somewhat warmer temperatures ruled for the most part. But the big news is that after a dry fall we had large amounts of rain in December, rounding out 2013 for the 10th highest annual rainfall since 1920.

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

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

Compared to November, more of the US was cooler than average. The upper midwest experienced temperatures 8 degrees F below normal, and combined with precipitation (see below), that meant a lot of snow and ice. Colder than normal temperatures stretched across the country in the north, and then a tongue of cold anomalies 4-5 degF below normal penetrated south through Texas.

For higher than normal temperatures, only much of California and a swatch centered in New Mexico and Arizona were warmer in the west. But a coverage of higher anomalous temperatures were the case for the southeast US, rising to 6 degF in Florida.

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

The incidence of higher than normal precipitation brought (or will bring, once the melt) relief to two major areas. The northern tier of western to midwestern states received a lot of what was probably snow. And in the southeast there was a broad brushstroke of much higher rainfall than we've seen in several months. The southern half of Florida continued its drier than normal weather seen in November. California is still in a drought period, to put it mildly, and that extreme extended up into the Pacific Northwest in November and December, at least. Much of the south west of the Mississippi was drier than normal, as was the central part of the country.

For the Athens, GA area:

Below is my usual daily rain/temperature plot visualizing the changes in temperatures and precipitation. The spiky lines are temperatures recorded roughly ten times a day, and the lighter blue columns are Wolfskin rainfall measurements.

The black line is the normal average daily temperature, and you can see that we've been both above and below that line in December. We had a long period of high temperatures in the first quarter of the month, some normality in the second quarter, and then another round of high temperatures for a few days in the third. The last quarter of the month was fairly normal in temperatures.

The real story here was the large amount of rainfall, starting with daily pissant amounts in the first quarter, and then nearly five inches of rain in a 24-hour period on Dec 22-23. Not inconsiderable amounts totalling 2.5 inches fell in the last few days of December.

On average, we were warm in December. The Athens area mean temperature during December was 2 degF above the average 45.4F. We broke one high temperatures record, on Dec 22, with 71F edging out 1948's 70F. We came close, within a degreeF, on Dec 6 and Dec 21.

We had 5 days more than 1 standard deviation above normal highs (average is 5.5 days), so the higher monthly temperatures were due not to high extremes. Rather, they were due to both duration - lots of days somewhat higher than normal - and record high low temperatures (at night). We only had 2 nights with temperatures more than 1 standard deviation below normal lows (average 4.4 nights). The number of events outside normality underscores the cooler temperatures the overall average reflects.

Let's look more closely at the breakdown in temperature ranges in December.

The monthly histogram below shows the breakdown of high and low temperature range counts from December 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 high temperature events fall within the error bars (except, perhaps, for the >= 70 degF days). It's the average, oddly, that's way above normal in significance. We had many more average days, and the small number of much more than average temperature days kicked us over the December average. Nighttime events, not so much significance.

The dry period that began in September, and continued throughout the fall, ended in December. The official Athens rainfall in December was 7.62 inches, more than twice the 3.73 inches average. Out here in Wolfskin we had 10.2 inches, nearly three times the December average rainfall.

And so that does bring us to the rain for our area: in short, a lot, a whole lot. 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.

We actually flirted a bit with exceeding the river of peach for much of the month, but in the last week or so we really exceeded it.

Here is a little taste of our 2013 rainfall accumulations out here in Wolfskin. Athens data may differ somewhat.

First, take a look at the following accumulations by month, for the years 2005-2013. The 2013 black line ends at the highest point in the 9-year period, at 64.44 inches for the year, 18 inches above average. It edges out the previous clear record set in 2009.

Now's an appropriate time to report our recovery from several drought periods. The figure below shows accumulated rainfall since January 2005 in green, plotted against the accumulated average in red. For years, we've been below the red.

The blue shows the difference, as indicated by the numbers on the right hand vertical axis. We're still below the zero point that would indicate we've achieved normal accumulations on a decadal scale. But we're back up to the levels we got to in 2009, and have eradicated the drought of 2011-2012.

I like the blue plot above - it clearly shows the two periods of drought, the 2005-2009 drought, the recovery in 2009, and the lesser but still significant drought of the last two years.

Prognosticator stuff:

What is the prognosticator telling us?

For us here in the southeast, it has been accurate over the last five months for temperature and precipitation, but its prediction of drier and warmer in the last half of December certainly failed for rainfall predictions.

So for what it's worth, as of 3 January, we'll have a higher than normal chance of precipitation for the next few weeks, then an equal chance, followed by a higher than normal chance of drier weather in the late winter and early spring.

Temperature-wise, it tells us in the Southeast that we can expect a couple of weeks of warmer temperatures (in the short term this is certainly not correct, and we might expect snow in the next few days). For the next three months (JFM), we'll have at least equal chances of being warmer than normal.

Take a look for your own region. In fact, there's now a very nice 2013-2014 winter outlook for everyone here.

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 30 December, ENSO neutral conditions continue, and are expected to remain neutral, now through the Northern Hemisphere summer. We've remained ENSO neutral now for 20 months. The last time we had such a lengthy period without an El Niño or La Niña must be at this point in the 1990s.

NOAA's Monthly State of the Climate product for November is available. There's a great map of significant weather events occurring during autumn 2013.

2012's annual report for is available regionally, nationally, and globally. Soon the report for 2013 will appear.

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