These data tables of meteorological elements outline the climatic conditions at major weather observing stations in all 50 states, Puerto Rico, and Pacific Islands. The data are from observing sites presently in use or include data from former sites that are comparable in exposure. Stations having less than three years of data for the current operating site are omitted from the tables of observed data. Data in this publication have been extracted from the Normals Means and Extremes table contained in the Local Climatological Data Annual Summary, published for individual stations.
The following gives a full explanation of all symbols and caveats used to explain the data values in the data tables.
I.Observed Data (Monthly and Annual) - These values are the means and extremes for the Period of Record (number of years) indicated. Period of record are documented in the Local Climatological Data annual publications. A. Temperature - Highest of Record, Degrees Fahrenheit (F) B. Temperature - Lowest of Record, Degrees Fahrenheit (F) The annual temperature entry for each station represents the highest or lowest observed temperature in any month. C. Mean Number of Days with Minimum Temperature 32 Degrees F or less. The mean number of days with a minimum temperature of 32 degrees F or lower indicates the frequency of occurrence of days with freezing temperatures. D. Mean number of Days with Precipitation 0.01 Inches or More This table shows mean number of days per month with at least 0.01 inch of precipitation. This is the smallest amount of precipitation numerically recorded, and includes the liquid water equivalent of frozen precipitation. The frequency of days with precipitation should not be considered as frequency of cloudy days. E. Snowfall (including ICE PELLETS and SLEET) - Average Total in Inches. NOTE: Beginning in April 1988 HAIL is also included under Snowfall. Therefore, some stations may show snowfall during the warm months. F. Wind - Average Speed (MPH) The average wind speed is based on the speed of the wind regardless of direction. G. Wind - Maximum Speed (MPH) This table expresses both a maximum wind speed for the stations and, where available, the direction (referenced to true North) from which it blew. Short gusts are listed only for stations denoted with a (G). If the direction is expressed as one of the 16 compass points (N, NNE, NE, etc.) the maximum speed is calculated from the minimum time during which one mile of wind passed the station. Note that some stations that report short gusts (G) may also use the 16 compass point reference for wind direction. If the direction is expressed numerically, the maximum speed is the highest one minute average value recorded by the observer. Direction is given in tens of degrees clockwise from true North. H. Sunshine - Average Percentage of Possible The total time that sunshine reaches the surface of the earth is expressed as the percentage of the maximum amount possible from sunrise to sunset with clear sky conditions. I. Cloudiness - Mean Number of Days - Clear (CL), Partly Cloudy (PC), Cloudy (CD) This table shows the mean number of days per category of cloudiness. The categories are determined for daylight hours only. Clear denotes zero to 3/10 average sky cover. Partly cloudy denotes 4/10 to 7/10 average sky cover. Cloudy denotes 8/10 to 10/10 average sky cover. J. Average Relative Humidity (percent) - Morning (M) and Afternoon (A) The relative humidity is expressed as a percentage measure of the amount of moisture in the air compared to the maximum amount of moisture the air can hold at the same temperature and pressure. Average humidity values are given for selected morning and afternoon observations. Maximum relative humidity values usually occur during morning hours. In this publication, the Local Standard Time (LST) of morning and afternoon humidities are shown below. Atlantic, Alaskan (M morning 8 A.M.) (Afternoon 2 P.M.) Eastern, Bering, 165W Meridian (M morning 7 A.M.) (Afternoon 1 P.M.) Central, 180E Meridian (M morning 6 A.M.) (Afternoon NOON) Mountain, 165E Meridian (M morning 5 A.M.) (Afternoon 5 P.M.) Pacific, 150E Meridian (M morning 4 A.M.) (Afternoon 4 P.M.) 135E Meridian (M morning 9 A.M.) (Afternoon 3 P.M.) II. Climatological Normals (Monthly and Annual) - these are the 30-year average values computed from the data recorded during the period 1961-1990. Normals are updated decennially, for the most recent 30-year period. If an instruments exposure was changed, mathematical adjustments are made to make the data representative of the current location. The values are statistically determined and cannot be recreated solely from the original record. A. Normal Daily Maximum Temperature, Degrees F B. Normal Daily Minimum Temperature, Degrees F. C. Normal Daily Mean (Average) Temperature, Degrees F. In A, B, and C above, the temperature data are the normal daily values for each month. They have been adjusted, as necessary. D. Normal Heating Degree Days (July-June) E. Normal Cooling Degree Days (January-December) Degree day data are used to estimate amounts of energy required to maintain comfortable indoor temperature levels. Daily values are computed from each days mean temperature (max + min/2). Each degree that a day's mean temperature is below or above 65 degrees Fahrenheit is counted as one heating or cooling degree day. F. Normal Precipitation, Inches The normal precipitation is the arithmetic mean for each month over the 30-year period, adjusted as necessary, and includes the liquid water equivalent of snowfall.
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