Worrisome Rain Forecast Over The Next Week

Over the next week in California, it looks like we're going to be hit twice, pretty hard, by rain. Temperature-wise, the first storm will be kind of marginal - perhaps crushing roofs in the mountains as rain freezes on top of rooftop snow - but the second storm will be quite warm, and therefore more worrisome. With such a deep snowpack already present in the Sierra Nevada, warm rain will mean rapid melting and potentially flooding.

“We’re going to see rain on top of snow, and for elevations of say 2,000 feet to about 4,000 feet, a lot of that snow is going to melt,” said Carlos Molina, a meteorologist with the National Weather Service in Hanford, Calif. “We’re going to basically lose a lot of the snow that fell from the previous storms. We’re looking at potential for flooding.” 

Indeed, the highest likelihood of flood-related impacts are in lower-elevation areas with unusually deep snowpack, Swain said. Small rivers and streams in those areas will see significant potential for runoff issues, as will some urban areas — particularly in places where storm drains are already clogged by snow. 

There may also be problems at elevations above 5,000 or 6,000 feet, he said. Though snowpack in such areas is probably too deep and too cold to be melted by the incoming storm, it can become heavier as it absorbs more water. That could cause roof collapses and other structural issues. 

“If you can go out and try and remove some snow from structures that might be vulnerable, do it,” Swain said. The state has already seen a spate of roof collapses from mounting snow, including a grocery store providing critical supplies in snowbound Crestline. 

Scott Rowe, a meteorologist with the weather service in Sacramento, said the incoming low-pressure system is originating in the north but is expected to link with “very warm” subtropical moisture coming from Hawaii. Such storms are sometimes referred to as a Pineapple Express and are known to drop heavy moisture in California. 

“We’re essentially transitioning from one storm track to another, where the moisture origins are coming from a warmer, juicier location,” Rowe said.