Heavy rain will inundate coastal Oregon and northern California into early next week, threatening serious flash flooding, mudslides and travel delays and cancellations.
A Pineapple Express will help to fuel the heavy rain as a storm plows into the Pacific coast through Saturday. The heaviest rain will soak Northern California during the day on Friday.
“A Pineapple Express is a continuous surge of tropical moisture extending from near Hawaii all the way into a West Coast storm,” AccuWeather.com Senior Meteorologist Bernie Rayno said.
This pattern can significantly enhance rainfall and threats such as flooding. Recent burn scar areas in California will be especially vulnerable to flooding and debris flows, since rain water cannot penetrate scorched ground.
Widespread rainfall amounts of 2-3 inches are expected in western Oregon and northern California, including in the Bay Area. In far northern California, amounts may exceed 5 inches through Saturday.
Lengthy flight delays and cancellations are possible at San Francisco International Airport on Friday due to low clouds and excessive rainfall associated with the storm.
Motorists may face travel problems on the ground as rain mixes with oil buildup on roadways to create slick conditions.
A second storm will arrive along the West Coast Sunday into Monday, unleashing another round of heavy rain.
The rounds of rain follow after an extremely dry January for many locations.
“This is the first significant rain [for Northern California] since the middle of December,” Clark said.
January 2015 went down in the record books as the driest January on record for San Francisco with no rain recorded.
Meanwhile, mountain snowpack is an important resource for filling reservoirs and water supply for drought-stricken California. It is crucial to look at snowpack when analyzing the potential impact of storms on the ongoing drought. However, mountain snow is not likely with the upcoming storms, Clark said.
“Snow levels, because of the warm subtropical flow, will be very high, above 8,000 feet most of the time,” Clark said. “Therefore, while the rains are welcomed, though too much in some places is not good either, these storms will be no help in putting down a snowpack.”
Keep checking back with AccuWeather.com for updates on the Pineapple Express setting up and any potentially life-threatening flooding that may result.