Determine whether a NOAA NARR variable selected for download is a monolevel or pressure level variable. Monolevel variables are derived from https://downloads.psl.noaa.gov/Datasets/NARR/Dailies/monolevel/, and pressure level variables are derived from https://downloads.psl.noaa.gov//Datasets/NARR/Dailies/pressure/.
narr_variable(variable)
list with URL base and vector of months (blank for monolevel)
character(1). User-selected NARR variable