A powerful, wet storm system called the atmospheric river is about to flood the San Francisco Bay area from Tuesday to Thursday, and Santa Cruz County officials are watching the forecast closely to determine whether to evacuate some residents in the mountains due to the risk of mudslides and debris flows.
“Our main goal is to get people out of the area so that we don’t have to rescue them because there is no way to stop the flow of debris,” said Armstrong. “We have been working on sending advance messages for weeks and months and making sure people know they are in areas with potential for debris flows. We told them to have an evacuation plan, to pack.”
The storm is expected to be the rainiest and strongest of the rainy season so far, with the heaviest rains from Tuesday night through Wednesday. Atmospheric rivers pull long clouds of water vapor into the atmosphere – on average, 250 to 375 miles wide – and are often called the river in the sky. On the west coast, they generally originate in the South Pacific and, as they travel from the tropics across the ocean, collect incredible amounts of moisture.
With the storm approaching, the National Meteorological Service estimates that the Santa Cruz Mountains could receive up to 25 centimeters of rain and that could create confusion in the 86,000 acres burned by the CZU Electrical Complex in August.
The weather service calculated the precipitation rate limits for the Santa Cruz mountain region and determined that mudslides and debris flows can occur if the rates reach 0.3 inches in 15 minutes, 0.5 inches in 30 minutes or 0.7 inch in 60 minutes.
“The areas of greatest concern in Santa Cruz are the two areas that have the greatest severity of burning at the head of steep drainages below the houses,” said Armstrong. “This is Swanton Road on the north coast of Santa Cruz County and the Boulder Creek community, especially as you go up the 236 highway corridor.”