Rainfall and Climate Variation over a Sloping New Mexico Plateau during the North American Monsoon

The distribution of rainfall and other climatic variables is studied over sloping terrain surrounding Los Alamos in northern New Mexico. Long-term rainfall records and over 10 years of data measured routinely from a raingauge array and several meteorological towers were analyzed. Results indicate that 36% of annual precipitation high on a plateau (at the base of the Jemez Mountains) falls during July and August, primarily from early afternoon convective showers. The showers typically begin around noon high on the plateau during July, while they are more evenly distributed during the afternoon and evening toward lower elevation (near the Rio Grande River valley). However, a secondary peak of rain intensity occurs during early evening high on the plateau and several hours later near the valley. Several possible reasons for the spatial and temporal variations are discussed. The showers also routinely influence afternoon insolation, temperature, and relative humidity, especially near the mountains. Downslope winds are more frequent in the afternoon, probably because of thunderstorm outflows.