A comparison between the 1991–2020 normals and the 2011 version of the 1981–2020 normals would not recognize this change to the underlying temperature time series, and would give the incorrect impression that the station was getting cooler. The discontinuity adjustment assigned was -0.68☌ (-1.22☏) starting in April 2017, which was subtracted from previous Januaries in this example, until another discontinuity was found in 2003, causing a further adjustment.
#Daily precipitation totals by zip code series#
This process aligns the whole time series with current station site and instrument characteristics so that it can be compared to today’s measurements, but it also creates substantial differences between the 20 normals calculations.įor example, the maximum temperature record for the KOKC station developed a substantial warming deviation from other nearby stations during early 2017 (see KOCK Oklahoma City - January Maximum Temperature). However, station-based temperature comparisons based on this same set of station normals are not reliable, because the homogenization process that removes artificial discontinuities (station moves, instrument changes, etc.) from station temperature data applies those adjustments to the entire dataset. The 1981–20–2020 station normals use data that was homogenized at different times (2011 for the first time period, and 2021 for the second). The non-climatic differences arise primarily from the fact that the 1981-2010 normals were calculated from the 2011 version of NCEI’s data holdings, while the 1991-2020 normals are based on a version from early 2021 which incorporates additions and corrections made to the historical record over the previous decade. The large-scale climatic differences are illustrated by the comparison maps shown above for which the same set of monthly gridded data was used to calculate averages for both periods. There are both climatic and non-climatic causes of differences between the two sets of normals. Many long-time users of NCEI’s station-based normals wonder how the 1991-2020 values that were released in 2021 differ from the 1981-2010 values released in 2011. overall and the reduction of precipitation in the West and increase in precipitation in the East as anticipated by models of future climate change The patterns of normals changes are following spatial trends in climate circulation dynamics and surface feedbacks, but still demonstrate the warmer conditions expected in the U.S. While annual normals changes were generally consistent, the single months showed pattern shifts that indicate a relationship to repeated preference of certain upper air wind patterns and storm tracks that shifted north or south with the seasons. Precipitation normals were generally wetter east of the Rockies, and drier in the central and southern West. to varying degrees, most distinctly in April. Overall, the central month of each season displayed cooling normals in the north-central U.S. The East was warm and displayed alternating zones of wetter and drier conditions that were reminiscent of shifting storm tracks. The rest of the country was consistently warmer, but the southwest and south-central U.S. marked both wetter and cooler normals for 1991–2020 than 1981–2010. Monthly gridded climate normals are available for the contiguous U.S., see the Gridded Normals tab for more information.Ī strong zonal pattern in the western two-thirds of the northern U.S. Many other important economic decisions that are made beyond the predictive range of standard weather forecasts are either based on or influenced by climate normals. These data allow travelers to pack the right clothes, farmers to plant the best crop varieties, and utilities to plan for seasonal energy usage. Climate Normals are the latest in a series of decadal normals first produced in the 1950s. normals every 10 years in keeping with the needs of our user community and the requirements of the World Meteorological Organization (WMO) and National Weather Service (NWS).
The official normals are calculated for a uniform 30 year period, and consist of annual/seasonal, monthly, daily, and hourly averages and statistics of temperature, precipitation, and other climatological variables from almost 15,000 U.S. Normals act both as a ruler to compare today’s weather and tomorrow’s forecast, and as a predictor of conditions in the near future. Climate Normals are a large suite of data products that provide information about typical climate conditions for thousands of locations across the United States.
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