How to read the Preliminary Climate Data Report
(Form F-6)
The Preliminary Climate Data (Form F-6) has 18 columns of data and one row for each day of the month. There are several summaries and definitions at the end of the report. Many of the data elements are self explanatory. A brief description of each column follows this sample (courtesy of WFO Buffalo). Some of the contractions used may be confusing. Click here to view the list of contractions commonly used by the National Weather Service. If a column is marked as either M or N/A that means that the data could not be collected and is missing.
  PRELIMINARY LOCAL CLIMATOLOGICAL DATA (WS FORM: F-6)
  
                                            STATION:   PHILADELPHIA
                                            MONTH:     JULY
                                            YEAR:      2003
                                            LATITUDE:   39 52 N                   
                                            LONGITUDE:  75 15 W                   
  
    TEMPERATURE IN F:       :PCPN:    SNOW:  WIND      :SUNSHINE: SKY     :PK WND 
  ================================================================================
  1   2   3   4   5  6A  6B    7    8   9   10  11  12  13   14  15   16   17  18
                                            AVG MX 2MIN
  DY MAX MIN AVG DEP HDD CDD  WTR  SNW DPTH SPD SPD DIR MIN PSBL S-S WX    SPD DR
  ================================================================================
  
   1  87  70  79   3   0  14 0.00  0.0    0  7.3 14 300   M    M   5        17 260
   2  86  69  78   2   0  13 0.03  0.0    0  7.5 16 200   M    M   7 18     21 180
   3  81  69  75  -1   0  10 0.17  0.0    0  8.1 16  40   M    M   9 1      21  30
   4  94  70  82   5   0  17 0.00  0.0    0  8.7 17 270   M    M   4 18     21 220
   5  95  76  86   9   0  21 0.08  0.0    0  9.7 32 290   M    M   4 138    45 270
   6  93  75  84   7   0  19 0.13  0.0    0  9.2 18 230   M    M   6 138    23 230
   7  92  72  82   5   0  17    T  0.0    0  8.0 20 230   M    M   5 13     23 240
   8  91  77  84   7   0  19 0.00  0.0    0 10.4 21 310   M    M   5        24 320
   9  90  70  80   3   0  15 0.01  0.0    0 10.4 22 270 335   38   8        26 270
  10  71  67  69  -8   0   4 0.19  0.0    0 10.6 16  80   M    M  10 13     21  10
  11  90  69  80   2   0  15 0.01  0.0    0  9.5 23 230   M    M   8 138    26 240
  12  88  69  79   1   0  14    T  0.0    0 11.9 23 240 396   45   5        29 300
  13  85  68  77  -1   0  12 0.01  0.0    0  6.5 16 230   M    M   6        18 220
  14  80  69  75  -3   0  10 0.16  0.0    0  5.7 12 110   M    M   6 1      14  80
  15  85  67  76  -2   0  11 0.00  0.0    0  6.4 14 180   M    M   3 1      16 170
  16  92  72  82   4   0  17 0.00  0.0    0 10.8 20 290   M    M   7        23 250
  17  87  68  78   0   0  13 0.00  0.0    0  8.2 17 360   M    M   1        22 360
  18  88  67  78   0   0  13 0.03  0.0    0  7.0 18 340 320   36   7 13     22 350
  19  86  68  77  -1   0  12 0.00  0.0    0  7.0 14 320 730   83   6 1      17 310
  20  88  65  77  -1   0  12 0.00  0.0    0  6.9 15 190   M    M   4        18 190
  21  92  72  82   4   0  17 0.00  0.0    0 11.2 23 180   M    M   7 18     28 180
  22  92  74  83   5   0  18 0.32  0.0    0 11.5 21 240   M    M   8 138    25 240
  23  83  73  78   0   0  13 0.05  0.0    0  9.0 17 200   M    M   9 1      29 230
  24  85  71  78  -1   0  13 0.57  0.0    0 11.0 20 240 595   68   7 13     22 240
  25  89  67  78  -1   0  13 0.00  0.0    0  6.6 14 220   M    M   2        18 310
  26  91  69  80   1   0  15 0.00  0.0    0 10.0 20 240   M    M   4 18     23 240
  27  93  76  85   6   0  20 0.17  0.0    0 13.9 36 260   M    M   8 138    44 260
  28  86  70  78  -1   0  13 0.03  0.0    0  7.8 15 230   M    M   8 1      18 230
  29  85  68  77  -1   0  12    T  0.0    0  6.3 16  80   M    M   6        18  80
  30  81  66  74  -4   0   9    T  0.0    0  6.7 13  90   M    M   6 8      15  90
  31  83  69  76  -2   0  11 0.05  0.0    0  9.5 16  50   M    M   9 1      30  80
  ================================================================================
  SM 2709 2172         0 432  2.01     0.0 273.3         2376    190              
  ================================================================================
  AV 87.4 70.1                               8.8 FASTST  PSBL  %   6    MAX(MPH)  
                                   MISC ---->    36 260                 45  270   
  ================================================================================
  NOTES:
  # LAST OF SEVERAL OCCURRENCES
  
  COLUMN 17 PEAK WIND IN M.P.H.
  .
  PRELIMINARY LOCAL CLIMATOLOGICAL DATA (WS FORM: F-6) , PAGE 2
  
                                            STATION:  PHILADELPHIA
                                            MONTH:    JULY
                                            YEAR:     2003
                                            LATITUDE:   39 52 N                   
                                            LONGITUDE:  75 15 W                   
  
  [TEMPERATURE DATA]      [PRECIPITATION DATA]       SYMBOLS USED IN COLUMN 16    
  
  AVERAGE MONTHLY: 78.7   TOTAL FOR MONTH:   2.01    1 = FOG                      
  DPTR FM NORMAL:   1.1   DPTR FM NORMAL:   -2.38    2 = FOG REDUCING VISIBILITY  
  HIGHEST:    95 ON  5    GRTST 24HR  0.61 ON 23-24      TO 1/4 MILE OR LESS      
  LOWEST:     65 ON 20                               3 = THUNDER                  
                          SNOW, ICE PELLETS, HAIL    4 = ICE PELLETS              
                          TOTAL MONTH:   0.0 INCH    5 = HAIL                     
                          GRTST 24HR     0.0         6 = GLAZE OR RIME            
                          GRTST DEPTH:   0           7 = BLOWING DUST OR SAND:    
                                                         VSBY 1/2 MILE OR LESS    
                                                     8 = SMOKE OR HAZE            
  [NO. OF DAYS WITH]      [WEATHER - DAYS WITH]      9 = BLOWING SNOW             
                                                     X = TORNADO                  
  MAX 32 OR BELOW:   0    0.01 INCH OR MORE:  16                                  
  MAX 90 OR ABOVE:  12    0.10 INCH OR MORE:   7                                  
  MIN 32 OR BELOW:   0    0.50 INCH OR MORE:   1                                  
  MIN  0 OR BELOW:   0    1.00 INCH OR MORE:   0                                  
  
  [HDD (BASE 65) ]                                                                
  TOTAL THIS MO.     0    CLEAR  (SCALE 0-3)   3                                  
  DPTR FM NORMAL     0    PTCLDY (SCALE 4-7)  19                                  
  SEASONAL TOTAL     0    CLOUDY (SCALE 8-10)  9                                  
  DPTR FM NORMAL     0                                                            
  
  [CDD (BASE 65) ]                                                                
  TOTAL THIS MO.   432                                                            
  DPTR FM NORMAL    37    [PRESSURE DATA]                                         
  SEASONAL TOTAL   682    HIGHEST SLP 30.29 ON 26                                 
  DPTR FM NORMAL   -29    LOWEST  SLP 29.71 ON 22                                 
  
  [REMARKS]
  
Column Explanations -- Column numbers are in parenthises ()
(1) - Day of the month ("calendar day"). Note that the time period is different between Standard Time and Daylight Savings Time. The calendar day is midnight to midnight Standard Time, but 1 a.m. to 1 a.m. DST.

(2) - Maximum temperature. This is the highest temperature (F) recorded for the calendar day.

(3) - Minimum temperature. This is the lowest temperature (F) recorded for the calendar day.

(4) - Average temperature. The sum of the previous two columns, divided by 2, and rounded, gives the value for this column.

(5) - Departure from normal. This value is derived by subtracting the "normal" temperature from the "average" temperature (column 4). The "normal" temperature is the 30-year smoothed average for the date, supplied by the National Climatic Data Center.

(6a) - Heating Degree Days. The average temperature (column 4), subtracted from 65, yields HDD. The amount of energy used for heating is almost directly proportional to the number of heating degree days.

(6b) - Cooling Degree Days. Similar to (6a) above, CDD are derived in the reverse manner. Sixty-five is subtracted from the "average" temperature (column 4). Again, energy usage is the main application of this value.

(7) - Precipitation (Water Equivalent). This is the amount of liquid precipitation, in inches, to the nearest hundredth, that has fallen during the calendar day. If frozen or freezing precipitation (snow, sleet, freezing rain, etc.) falls, it is melted and added to the total of any liquid precipitation.

(8) - Snowfall. This total, where measured, is the amount of snow, hail, or ice pellets, in inches, to the nearest tenth, that falls during the calendar day. In this case, the frozen precipitation is not melted before measurement. Typically, snowfall is about 10 times its water equivalent (see column 7), but this ratio can vary dramatically when snow falls at temperatures above freezing - or well below freezing.

(9) - Snow depth. The depth of frozen precipitation (whether snow, ice, or hail) on the ground at 6 a.m. Standard Time (7 a.m. DST), in whole inches, is shown here. The value is the actual depth of the snow and ice, without including such things as grass underneath.

(10) - Average wind speed. The calendar-day average wind speed is shown here, in miles per hour, to the nearest tenth. This value is normally derived by dividing the total "distance" of the wind (as measured by an anemometer) and dividing by 24. Note that wind speeds during the daylight hours tend to be substantially stronger than those that occur at night.

(11) - Fastest 2-minute speed. The strongest 2-minute average wind speed that occurs during the calendar day is identified here. The units are miles per hour. By definition, this value must be less than the peak gust (column 18) and more than the daily average (column 10).

(12) - Fastest 2-minute direction. (See column 11 for information on the "fastest 2-minute wind.") This is the prevailing direction of the strongest 2-minute wind, expressed in tens of degrees. North is 36 (north could also be shown as 0, but 36 is used here); east is 09; south is 18; west is 27; and all other directions are in-between. Northeast, for example, would be shown as either 04 or 05, since it is 45 degrees clockwise from north.

(13) - Total minutes of sunshine. Where available, this value is the approximate number of minutes that the sun is detected as shining, according to a sunshine indicator.

(14) - Percent of possible sunshine. Where available, this is the ratio of the value in column 13 with the number of minutes between sunrise and sunset, expressed as a percent.

(15) - Sky cover. This entry is no longer available. It was previously used to show the number of tenths of cloud cover, as an hourly average through the daylight hours. This Not Available.

(16) - Weather occurrences. The numbers presented in this column are described in a chart at the lower right of the Form 6.

(17) - Peak gust direction. This is the direction associated with the strongest gust of wind measured during the calendar day. See the description of column 12 for details on the coding.

(18) - Peak gust speed. The strongest wind gust measured during the calendar day is recorded here, in miles per hour.