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Mar 18 2011

Cold winter + hot summer + cold winter = “normal” 2010

By Ian Millar

The coldest winter (December through February) in the last 140 years on Seabrook-Kiawah was 1977/78 when the mean temperature would have been 44.2 ⁰F (see chart). The mean temperature for winter 2010/2011 was 46.5 ⁰F. That made it the 17th coldest winter in the last 140 and made it just slightly colder than the 2009/2010 winter. Breaking winter down into its components, we see that the mean temperature for December 2010 was an extremely chilly 42.6 ⁰F (the third coldest December) and that its counterpart for January 2011 was a very chilly 44.2 ⁰F (the 19th coldest January) whereas the mean temperature of February 2011 was a more typical 52.6 ⁰F. This past December was so cold that we set two new daily low records of 26.6 ⁰F and 22 ⁰F for December 8 and 14, respectively.

However, we had plenty of company being chilly! According to the records it maintains back to 1895, NOAA (the National Oceanic and Atmospheric Administration) reported that the state of South Carolina had its third coldest December, as did North Carolina. The same report highlighted that the states of Georgia and Florida had their coldest Decembers on record.

With one eye on what next winter may hold for us, it’s worth pointing out that winter mean temperatures here can vary significantly from year to year and that the temperature history shows we have not experienced more than two very cold winters in a row (see chart). After our experience of two very cold winters in succession, it may be reasonable to expect that next winter will be warmer.

These past two winters’ unusually cold temperatures contrasted with our 2010 summer (June through August) which we recorded as the second hottest Seabrook-Kiawah summer in the last 140 (see chart). Only the summer of 1998 was hotter. So what effect did an extremely hot summer and an extremely chilly January, February and December have on the mean temperature for the whole of 2010? Well, the annual mean temperature turned out to be 65.1 ⁰F (see chart) which was just slightly below the 140 year average of 65.3 ⁰F. In that context, it was a fairly normal year. Remember, climate is what we expect and weather is what we get.

Note: to establish the Seabrook-Kiawah temperature history, we use the data from three active weather stations on the islands of Seabrook and Kiawah. Those data go back no further than the year 2000. However, the various temperature relationships for each season and each month between Seabrook-Kiawah and Charleston’s downtown have proven to be consistent over the last 11 years. We apply those relationships to the Charleston City weather station data to impute a history for Seabrook/Kiawah temperatures before the year 2000. This allows us to take advantage of the Charleston City weather data, some of which go back as far as 1871.

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