Downslope Afternoon Winds
During the forenoon, in the absence of an overriding general wind flow, local winds tend to be upslope and flow up the draws on both the west and east sides of the Coast Ranges. Usually, the flow through gaps and saddles is easterly because of the stronger heating on the east side in the forenoon. The two flows meet in a convergence zone on the west side of the ridge. By midday the flow up the west slopes has increased, most likely because of the sea breeze or a strengthening of the monsoon circulation due to intensification of the thermal trough. The convergence zone has moved eastward across the ridge, and the flow through the gaps has changed to westerly.
Waves form in this westerly flow, which first remain aloft on the lee side of the mountains, and later surface to cause strong downslope winds on the east side. Downslope afternoon winds are commonly three times as strong as the forenoon upslope winds. In some areas, downslope afternoon winds occur nearly every day during the warm season, while in other areas they occur only occasionally. The time of the wind shift from upslope to downslope on the east side may vary from late forenoon to late afternoon, but most frequently it is around noon or early afternoon. On some days, upslope winds redevelop in late afternoon as the mountain waves go aloft. On other days, the downslope afternoon winds diminish and change to the normal nighttime drainage winds.
Encyclopedia ID: p414
