Go to National Environmental Satellite, Data, and Information Service Home Page. Go to National Oceanic and Atmospheric Administration Home Page.
NOAA Logo, National  Environmental Satellite, Data, and Information Service. National Climatic Data Center, U.S. Department of Commerce
DOC > NOAA > NESDIS > NCDC
Land-Based Data / NNDC CDO / Product Search / Help

Climatic Data OnLine (CDO)


Global Climate Station Summaries (TD3505)
ISD Summary – Relative Humidity Statistics Help

Definition: The relative humidity (RH) is a ratio between how much moisture is in the air to how much moisture it would have if saturated at the same temperature and pressure. It is always expressed as a percentage.

Purpose: This summary shows the percent frequency of occurrence of RH values greater than or equal to any of 10 humidity threshold values (every 10% between 0% and 90%)  for individual hour categories and all hours combined. Mean values of RH are also given for each hourly category along with the number of observations used to calculate the mean and frequencies. (#OBS). This number is based on the number of valid observations available in the ISD database for the chosen location-periods. Users define the weather station(s) by city, month(s) and the period of time with which to calculate the statistics.


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.