In the universe of sources of weather and climate data across the Earth, NOAA’s National Climatic Data Center (NCDC) in Asheville, North Carolina has to be the big Kahuna. This center is the official federal archive of all weather and climate information collected by the National Weather Service as well as many other official climate databases both in the United States and around the world. They have data going back in time to when surgeons collected weather data at the frontier forts on the edges of the developed United States (1820s to 1840s) and climate data for places as far off as Bhutan (I know because I’ve used it before). They are also the official source of “blue ribbon certified” weather data, which some states (but not all) require in legal cases. The data on the site is mostly free (except for the certified data) but it can sometimes be hard to find exactly what you want. But if it was measured and archived, then it is likely that it is available somewhere at NCDC.
NCDC has recently merged with two other NOAA data centers, the National Geophysical Data Center, and the National Oceanographic Data Center, to become the National Centers for Environmental Information. For now, NCDC can still be reached at http://www.ncdc.noaa.gov.
If you have trouble finding information on their web site, please feel free to contact me for advice on how you might be able to find what you are looking for. There are a number of other sources of the same official information from Regional Climate Centers (more on them next week) that are sometimes a bit easier to work with.