This Portable Document Format (PDF) contains information about the Hourly Climate Normals from 1981 to 2010.  The 1981-2010 Normals comprise all climate normals using the thirty year period of temperature, degree days, precipitation, snowfall, snow depth, wind, etc.  Data is organized into hourly, daily, monthly, seasonal and annual normals.  This document describes the elements and layout of the Hourly Normals which are derived from a composite of climate records from numerous sources that were merged and then subjected to a suite of quality assurance reviews.The hourly normals provide a suite of descriptive statistics based on hourly observations at a few hundred stations from across the United States and its Pacific territories.  Statistics are provided as 30-year averages, frequencies of occurrence, and percentiles for each hour and day of the year.  These products are useful in examination of the diurnal change of a particular variable.For temperature, dew point and mean sea level pressure an average hourly value as well as a 10th and 90th percentile of hourly values is given.  For heating and cooling degree hours, an average hourly value is given using a 65 degree F base.  Average hourly values are also given for heat index and wind chill.  Cloud cover statistics include percent frequency of clear, few, scattered, broken and overcast conditions.  Wind statistics include prevailing and secondary wind direction and percent frequency, average wind speed, percentage of calm winds and mean wind vector direction and magnitude.The statistics are computed from the ISD-lite dataset for which more information can be found.  262 stations were selected from the ISD-lite data, based on their completeness and membership in a list of what were known as "first order stations."  These are typically airport locations with the needed 24 hours/day observations to make hourly normals meaningful.  All stations had at least 27 of the 30 years represented.Each hourly normal is computed on the basis of 450 possible values.  This is the aggregation of the value for a particular date and time, plus and minus 7 days, over each of 30 years.  If fewer than 350 valid values are present, the output is given as the special value 9999.  No normals are computed for February 29, but data for February 29 is included in the 15 day window for leap years.  The original data has been shifted from Greenwich Mean Time to an end product in local standard time.For additional information, please contact the National Climatic Data Center (NCDC) at Health Datapalooza focused content that may interest you: Health Datapalooza Health Datapalooza

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