To construct the best historical drought atlas, the best weather stations needed to be used. To establish the best stations, criteria needed to be established for screening the available stations. Using precipitation records from the National Weather Service Cooperative data (COOP) that is archived by the Regional Climate Centers (RCC) in their Applied Climate Information System (ACIS) as the basis for the data, the following criteria were established for the Drought Atlas:
- The station had to currently be open and taking regular observations
- The station had to have a minimum of 40 years of data available, going backwards from 2009
- The station could not have more than 2 consecutive months of missing data at any time in the period of record
- A unique period of record (POR) was established for each station based on meeting the stated criteria
Using the 12,000+ stations in the COOP database, two screenings of the data were done. The first screening looked for stations that had at least 30 years of data in their record and had 80 percent or more of the data available. A report for each station was made showing the months that had missing data for each year. By looking at the most current data and going back in time, we determined for each station how far back the data met our criteria. Gaps in the records were investigated to determine if the data existed somewhere else. The National Climatic Data Center (NCDC) provided access to scanned copies of the COOP forms in their archive via the Web Search Store Retrieve Display (WSSRD) system, which has transitioned over to the Environmental Document Access and Display System (EDADS), for this investigation. By comparing the data that was available on paper with the gaps in the digital archive in ACIS, we identified 288 stations for which the data gaps could be rectified and entered into the digital ACIS archive. The High Plains Regional Climate Center (HPRCC) staff keyed in the data for the gaps we identified using WSSRD, and these stations were then used in the atlas project. After consulting with several experts, we determined that a 30 year record is good, but using 40 years of data would be best, so we adjusted the initial station query to include just the stations with 40 or more years of data.