How Atmospheric Rivers Create Mudslide Conditions

Yet another atmospheric river is upon us.

Strong winds flowing across the Pacific Ocean create narrow bands of high moisture; the intensity of each atmospheric river depends on wind speed and direction. This causes heavy bands of rain along the coast, and lift along the mountains makes for heavier rain and even snow– like the rain we saw falling across the area Monday. 

Tuesday there will be a brief break in precipitation, and even some possible patches of sunshine. On Wednesday, a bit more rain is forecast and, and at higher elevations, snow– and it looks like a dusting a snowfall is possible pretty close to the coast.

Atmospheric rivers also bring with them the perfect conditions for possible mudslides. Topsoil over a more compacted layer of subsurface soil becomes saturated during heavy rains. Once the topsoil layer can’t hold any more water, it becomes unstable and can slide down a sloped surface.

Areas recently affected by wildfires are also at an increased risk of slides, as fire can leave behind a water repellent layer beneath the surface soil.  heavy rains can destabilize the top layer, leading to a flow of debris like ash and burned vegetation to slide down the slope. The California Office of Emergency Services advises drivers to take caution near hillsides and burn scars from past wildfires and warns drivers not to attempt to drive through a mudslide or debris flow.