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Message from Sam TN
We use 1981-2010 to determine "average" now. A few years back it was 1971-2000. That got moved up. Obviously, we would not want to use 1971-2000 or 1961-1990 or we would always be above normal due to global warming. It's sensible to use the last 30 years as a delta t since the change in normals should dictate how often the new norm gets moved forward in time. Many tell me often,"oh the air is more polluted now!" because of all the standards that are violated. No...the air is much better now than 1970 when the Clean Air Act was established. Standards have tightened. Same thing here: air has warmed.When it gets below average now, it might only be average vs. where we were 30 years back.
"In the strictest sense, a "normal" of a particular variable (e.g., temperature) is defined as the 30-year average. For example, the minimum temperature normal in January for a station in Chicago, Illinois, would be computed by taking the average of the 30 January values of monthly averaged minimum temperatures from 1981 to 2010. Each of the 30 monthly values was in turn derived from averaging the daily observations of minimum temperature for the station. In practice, however, much more goes into NCEI's Climate Normals product than simple 30-year averages. Procedures are put in place to deal with missing and suspect data values. In addition, Climate Normals include quantities other than averages such as degree days, probabilities, standard deviations, etc. Climate Normals are a large suite of data products that provide users with many tools to understand typical climate conditions for thousands of locations across the United States."
I hope this helps some here.
FYI, this El Niņo will be the warmest ever in region 3.4 this week or the next likely. Update coming tomorrow from NOAA.
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