It has recently been shown that under horizontally homogeneous conditions thunderstorm initiation locations during the summer in the central Rocky Mountain region are strongly influenced by the environmental winds (Tucker and Crook 2005). Thus, if the predominant direction and speed of the wind were known, there would appear to be potential for forecasting seasonal precipitation.

In practice, precipitation amounts are strongly influenced by the larger scale atmospheric conditions. Precipitation amounts and departures from normal are highly correlated. But some predictability does appear to exist for the departure of each station's precipitation from the regional average departure from normal.

In other words, if the mean wind directions and speeds are favorable for thunderstorms to initiate near a station but are unfavorable for a relatively nearby station, both stations may have above normal precipitation for the month but that of the former would be much above normal. These principles will be illustrated for stations in the central Rocky Mountain region for years with contrasting mean 500 mb wind directions using drainage basin means and average departures as a reference.

Tucker, D.F. and N. A. Crook, 2005: Flow over heated terrain. Part II: Generation of convective precipitation. Mon. Wea. Rev., 133, 2565-2582.