a. During wet winters in the Pacific North-
west and dry winters in the Southwest.
b. During dry winters in the Pacific North-
west and wet winters in the Southwest.
Figure 5. Positions of the North Pacific
high pressure ridge and atmospheric cir-
In general, precipitation from winter frontal storms makes up an increasingly
large portion of the total annual rainfall farther to the north in the study area
(Table 3). Flooding due to areally extensive and long-duration winter frontal
storms generally occurs in large drainage basins because all portions of the
drainage basin contribute to runoff. Rainfall intensities are generally too low to
impact smaller, steeper watersheds.