The yardstick for comparing temperature and precipitation to what is normal for South Dakota has changed thanks to an updated set of long-term averages.
That means weather watchers scale for normal precipitation anticipates more rainfall than before at many locations across the state, a South Dakota State University expert said, while normal winter low temperatures are not as severe in many places.
Dennis Todey, South Dakota state climatologist for the South Dakota Cooperative Extension Service, said the change takes effect starting in July 2011 in many agencies that use weather data. Weather forecasters and others who track weather data will start using a new set of 30-year averages updated for the period 1981 to 2010.
The take-home message for most people is that with any kind of a program that is comparing to some sort of an average, those numbers are going to change now. Just be aware of that and make sure that if you need to compare to some sort of average that you are getting the most current set of data involved looking at those averages, Todey said.
Todey explained that the official averages that are used by the federal government and any kind of federal program are the 30-year averages that are calculated by the National Climatic Data Center, updated every 10 years.
Previously, we compared everything to the 1971 to 2000 averages, Todey said. The National Climatic Data Center has done very quick work this year and done the calculations on the previous data. As of July 1 they released the new version of the 30-year averages, or the normals, as theyre officially called, from 1981 to 2010.
The National Climatic Data Center has installed the new averages on their weather and climate products. The National Weather Service will be installing them on their products starting in July. South Dakota State Universitys state climate office will install them as soon as possible so that people can compare weather data to those normals.
Todey said once his office has had a chance to look more closely at the new normals, hell also have a better idea of how the 30-year averages are shifting around the state. But already the state climatologist has a pretty good idea about some of the general trends.
I fully expect well see some changes upward in precipitation, that precipitation averages will become higher than they were before. I did have a chance to look at the Brookings station and it did show a fairly big increase in Brookings, but weve not had a chance to look at those in detail across the state, Todey said.
Todeys initial expectation is that 30-year average temperatures will also change.
The changes that we know we have seen are changes upward in minimum temperatures, especially in winter.
Todey will know more once hes had a chance to look at the data, but he notes that the 1970s are dropping out of the 30-year average, and there were several cold winters then, compared to several more mild winters in the past decade. Summertime highs may have eased downward as well in at least parts of the state.
Summer temperatures are cooler for some stations, but not much change for others.
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