Using the Software Program Surfer by Golden Software (version 8) a krig analysis was performed on the data. With 9 return periods and 9 durations, 81 distinct isohyetal plots were generated. This analysis was done in 2 steps using a VB program written specifically for this task.
Step 1 - Grid Creation Sheet.BAS - The first program (text file BAS extension) read the data from the spreadsheets for each return period and produced a Surfer grid file. The program also "blanked" ( Blanking.bln ) a section of the grid so that contours would only be drawn in certain parts of the final analysis. Nugget effect was applied with a variation coefficient of 0.25.
Step 2 Plot Creation.BAS - A second VBA application was run that read the grid files, formatted the plot, put the state background into the plot, and exported the results into a word doc file for viewing. The resulting srf files and doc files are included in the zip file.