Jan Null, CCM
Golden Gate Weather Services

• Source: "Comparative Climatic Data", National Climatic Data Center, NOAA, 2001

The following gives a full explanation of all symbols and caveats used to explain the data values in the above 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 Maxium Temperature 90 degrees F or More 
              (70 Degrees F or More for Alaska Stations)

   E.       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.

   F.        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.

   G.        Wind - Average Speed (MPH)

             The average wind speed is based on the speed
             of the wind regardless of direction.

   H.        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.

   I.        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.

   J.        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.

   K.        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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