•Water from the Rocky Mountains drains eastward through a number of deep canyons.
•In summertime, either when weak low pressure develops on the plains southeast
of the
mountains, or high pressure develops to the northeast, the flow on the plains east
of the
Rockies become easterlies.
•Afternoon heating can combine with the moist easterly flow toward the mountains
to produce
towering thunderstorms that anchor over the foothills just east of the mountain peaks.
•When these storms remain near-stationary over the foothills, flash floods can be produced from these heavy rainfall events.