Seasonality of precipitation along a meridian in the western United States

We investigate seasonality of daily precipitation along a meridian in the Western U.S. using a nonparametric technique. The occurrence of daily precipitation is treated as a nonhomogeneous Poisson process and the time varying intensity function is estimated for every calendar day using a kernel estimator. The technique is fully data adaptive. We apply this technique to selected long record stations along a meridional transect spanning from Tucson, AZ to Priest River ID. Differences in the seasonality of precipitation occurrence and magnitude are revealed as a function of latitude and topographic factors. A monotonic trend in the seasonality of precipitation over the length of record is also observed.