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Climatic Data OnLine (CDO)


Global Climate Station Summaries (TD3505)
ISD Summary – Sky Cover (Frequency of Occurrence) Help

Purpose: This summary shows percent frequency of occurrence per hour of the extent of sky coverage (by clouds or other obscuring atmospheric phenomena) at one or more weather station locations. The summary will differentiate between times of day for all sky cover amount categories. Users define weather station(s) by city, month(s) and the period of time with which to base the frequencies of occurrence.


Sky Cover Amount Abbreviations: Columns in the table are headed with abbreviations corresponding to the weather events defined below:

  • CLR = Clear (0 eighths of sky covered by clouds)
  • FEW = Few (1-2 eighths of sky covered by clouds)
  • SCT  = Scattered (3-4 eighths of sky covered by clouds)
  • BKN  = Broken (5-7 eighths of sky covered by clouds)
  • OVC = Overcast (Sky is completely covered by clouds)
  • W0X = Total Obscuration (Sky is not visible due to obscuring phenomena such as fog, smoke, etc.)
  • -X = Partial Obscuration (Sky is partially not visible due to obscuring phenomena such as fog, smoke, etc.)
  • #OBS = The number of observations in the time range used to determine the percentage values for each category

Date Restrictions

Choosing Date Range gives the user the available data over the period of record (e.g. between the selected dates).
Choosing Selected Dates gives the user the available data for the individual dates selected. Summaries will be generated over the entire range of years, days, and hours selected for each month.


Time Information: Time ranges in the table are located in the leftmost column and are represented by a number for the hour from 0 to 23 as follows:

  • 0 indicates from midnight through 12:59 am UTC
  • 1 indicates from 1:00 am through 1:59 am UTC
  • 2 indicates from 2:00 am through 2:59 am UTC
  • 3 indicates from 3:00 am through 3:59 am UTC
  • 4 indicates from 4:00 am through 4:59 am UTC
  • 5 indicates from 5:00 am through 5:59 am UTC
  • 6 indicates from 6:00 am through 6:59 am UTC
  • 7 indicates from 7:00 am through 7:59 am UTC
  • 8 indicates from 8:00 am through 8:59 am UTC
  • 9 indicates from 9:00 am through 9:59 am UTC
  • 10 indicates from 10:00 am through 10:59 am UTC
  • 11 indicates from 11:00 am through 11:59 am UTC
  • 12 indicates from 12:00 pm through 12:59 pm UTC
  • 13 indicates from 1:00 pm through 1:59 pm UTC
  • 14 indicates from 2:00 pm through 2:59 pm UTC
  • 15 indicates from 3:00 pm through 3:59 pm UTC
  • 16 indicates from 4:00 pm through 4:59 pm UTC
  • 17 indicates from 5:00 pm through 5:59 pm UTC
  • 18 indicates from 6:00 pm through 6:59 pm UTC
  • 19 indicates from 7:00 pm through 7:59 pm UTC
  • 20 indicates from 8:00 pm through 8:59 pm UTC
  • 21 indicates from 9:00 pm through 9:59 pm UTC
  • 22 indicates from 10:00 pm through 10:59 pm UTC
  • 23 indicates from 11:00 pm through 11:59 pm UTC
  • ALL indicates from midnight to 11:59pm UTC

Please note that all times are UTC (Universal Time Coordinate) and must be adjusted for local time if desired.