The YYYY_frost_depth.csv files contain frost depth measurements in terms of inches below the soil surface. 
Each file contains one hydrologic year's worth of frost depth data. A hydrologic year is a 12-month period between October 1st of one year and the next. 
For instance, the 2014_frost_depth.csv file will contain data from October 1, 2013 to October 1, 2014. 
 
The area of data coverage is limited to the National Weather Service North Central River Forecast Center service area. 

For data outside of this area of coverage, please contact the National Weather Service Weather Forecast Office (https://www.weather.gov/srh/nwsoffices)
or River Forecast Center (https://water.weather.gov/ahps/rfc/rfc.php) servicing your area of interest. 

Frost depth reports are commonly from frost tube instruments, visual reports from construction or cemetery sites, or other types of electronic probes.
The data in this file are pooled from a number of networks. Please note that the data collection instruments and methods may differ between networks. 

This data has not been quality controlled; Please use it with care.

If you have questions about this data please contact the North Central River Forecast Center at 952-361-6650 or w-ncrfc.webmaster@noaa.gov. 

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Data Fields: 
-nws_id = National Weather Service ID for the measuring site
-physicalelement = parameter code, where GD stands for "Frost depth, depth of frost penetration, non permafrost"
-extremum = Single-character descriptor which allows identification of maximum and minimum values
-datetime(GMT) = date and time at which the measurement is valid, in terms of Greenwich Mean Time (GMT)
-frostdepth(in) = frost depth measurement in terms of inches below the soil surface
-sitename = Descriptive name for the measuring site
-sitestate = Two letter acronym for the U.S. state in which the site is located
-wfo = Weather Forecast Office. This column contains the three-letter acronym for a National Weather Service Weather Forecast Office
-latitude = latitude
-longitude = longitude