Status and Version Information for U.S. Climate Reference Network Data

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Version change:     2.1 to 2.1.1
Commencement Date:  2017-06-20
Completion Date:    2017-06-30
Variables impacted: Precipitation

    Effective June 30, 2017, recalculation using the Official Algorithm
for Precipitation (OAP) 2.1.1 has been completed. The purpose of this 
recalculation is described in Appendix A of the OAP 2.1 documentation:
https://www1.ncdc.noaa.gov/pub/data/uscrn/documentation/maintenance/2016-05/USCRN_OAP2.1.Description_PrecipChanges.pdf

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Status change:      Correction
Correction Applied: 2017-05-01
Variables impacted: Precipitation for 3 stations
	
    From July 2016 until May 1, 2017, the precipitation values for 
the following stations and time periods were mistakenly missing on 
the website and in the FTP product files:
		NC Asheville 8 SSW          2004-05-01 to 2004-11-01 
		SC McClellanville 7 NE      2005-05-01 to 2005-11-01
		CA Stovepipe Wells 1 SW     2004-05-01 to 2005-06-01
Precipitation data for these stations/time periods that were downloaded
during the affected time period should be re-acquired. 

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Version change:     2.0 to 2.1 
Commencement Date:  2016-05-12 
Completion Date:    2016-06-13
Variables impacted: Precipitation
                    Relative Humidity (RH)
                    Temperatures from RH Sensor
                    Thermometer Shield Aspiration Fan Speeds
                    Air Temperature (when fan speeds are low)
                      
    Beginning May 12, 2016, USCRN changed the current data set to 
version 2.1 from v2.0. This version change was retroactively applied to 
all USCRN/USRCRN stations for their period-of-record 5-minute measurements 
from 2016-05-12 until 2016-06-13. [Note that during this period of 
reprocessing, data on the website and in these FTP products contained 
a mixture of v2.0 and v2.1 values.]
    Version 2.1 includes minor precipitation algorithm changes and 
changes/additions to the quality control ranges for acceptable 
relative humidity (RH) values, temperatures measured with the 
RH sensors, and for the speed of the fans which are used to 
aspirate the air temperature sensors. For precipitation, the Official 
Algorithm for Precipitation (OAP) v2.1 was implemented which  
addresses a minor correction to v2.0 that guards against
overally large (> 0.3 mm) precipitation residuals from one hour 
being transferred to the next hour. Further information can be found at 
http://www.ncdc.noaa.gov/crn/documentation.html.

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Version change:     1.0 to 2.0 
Commencement Date:  2015-08-17
Completion Date:    2015-09-15
Variables impacted: Precipitation

    The original Official Algorithm for Precipitation 
(OAP) version 1.0 was operational until August 17, 2015 and used a 
pairwise comparison and moving reference depth to calculate 
precipitation. Precipitation data accessed and/or downloaded 
prior to this date were calculated using OAP v1.0. 
    Beginning August 17, 2015, all precipitation data were 
calculated using a new processing algorithm, OAP v2.0. In addition, 
the v2.0 algorithm was retroactively applied to all USCRN/USRCRN 
stations for their periods of record (PORs) starting when 5-minute 
data began being collected. The reprocessing took approximately four
weeks to recalculate all station's existing values from v1.0 to v2.0
for their PORs and was completed on September 15, 2015. 
    OAP v2.0 marked a fundamental shift in the procedures used to calculate 
precipitation. The new algorithm uses a weighted average approach 
based on each sensor's noise level. It has greatly improved the 
network's capacity to detect lighter precipitation with greater 
confidence. For details, see Leeper et. al., 2015, 
(http://journals.ametsoc.org/doi/abs/10.1175/JTECH-D-14-00185.1) and
http://www.ncdc.noaa.gov/crn/documentation.html.

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