I need US monthly climate data for the years 1992-2012. It would be great to get down to a county level, but by state would be just fine. Every site that I go to inevitably kicks me to the NCDC, but I cannot make sense of their data.

For example: the .csv sample data for GHCN Monthly Summaries lists EMXT (extreme maximum temperature) for each month of 2010 in Petersburg, ND. July had an EMXT of 317. I've been through the documentation, but I can't figure out what that number is supposed to mean. I know it wasn't 317F or C in ND at any point. Did they add all the temps up? Was it around 10C every day of July 2010? But why would you do that? The .PDF data looks like actual temperatures, but I need a lot of data: .CSV is ideal; .PDF is really not useable for the amount of data I am going to manipulate.

What am I missing? Or is there another way to get this data?


The documentation linked from the datasets page states:

Air Temperature (all units in Fahrenheit on PDF monthly form and tenths of degrees Celsius on CSV or text)
EMNT - Extreme minimum temperature *
EMXT - Extreme maximum temperature *

The Petersburg data looks plausible under this interpretation (EMXT −3.9°C to 33.9°C over the year).

  • $\begingroup$ Well, that's embarrassing. I'm going to blame it on the brain-melting drugs I'm on for a dislocated vertebra. Do you have any idea why it would be in tenths of degrees C? Why not whole degrees? $\endgroup$ – Alanna Apr 5 '15 at 20:20
  • $\begingroup$ @Alanna We've all been there :). I wasted a good hour yesterday fruitlessly wrestling a data format because I somehow failed to see a vital bit of the extensive documentation. As to why they use that unusual unit, I have no idea. I think a tenth of a degree Celsius is around the accuracy you can expect from a typical weather station, but that doesn't explain why they don't just report it in degrees with one decimal place. $\endgroup$ – Pont Apr 5 '15 at 22:18
  • $\begingroup$ I've worked with one or two days sets that use tenths of a degree. Maybe it was felt that this would help prevent errors handling floats when the CSV was imported? Just a guess. $\endgroup$ – rensa Apr 5 '15 at 23:04
  • $\begingroup$ @Alanna: regarding the usage of tenths of a degree, it may be a continuation of an ancient data format from the early era of computers. Removing decimal points changes numbers to integers. In old computers memory capacity & calculating speed was an issue. In binary digits, integers are half the size of floating point numbers & a quarter the size of double precision numbers. Hence the use of integers speeds up calculations & requires less memory (disk drives, tape & RAM) than floating point numbers. In the old days, tape was used heavily as an external storage medium. $\endgroup$ – Fred Apr 6 '15 at 2:35
  • $\begingroup$ @Fred My advisor made his PhD student learn Fortran because so much climate data is still in that language. There are a number of reasons for this. I can see why, then, not having decimals, as you say, would make sense. Thank you so much! $\endgroup$ – Alanna Apr 6 '15 at 6:33

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