Additional storms bearing rain, locally gusty thunderstorms and high-elevation snow will take aim at California and the balance of the western United States into the Memorial Day weekend. “A block in the jet stream is forcing storms to take a much more southern route onshore into western North America than usual for the latter part of May,” according to AccuWeather Senior Meteorologist Brett Anderson. The first storm in the series brought disruptive snow and record-setting rainfall to California last Wednesday into Thursday. The second storm brought more rain and mountain snow to California on Sunday. In the wake of this system, dry conditions will briefly take hold across most of the state on Monday.
Authorities reminded residents Sunday shelter from lightning as showers and scattered thunderstorms were forecast for Southern California. The storm was expected to move through the region Sunday night and all Monday, and bring dry and wet thunderstorms, according to the National Weather Service. Weather officials warned of dangerous lightning over land and water and reminded residents that conditions can change quickly, especially in the mountains.
The ominous gray clouds hovering above Los Angeles on Tuesday aren’t likely to produce much more than the occasional sprinkle for the region before summer-like temperatures return later in the week. The dash of moisture, which forecasters say will be mostly focused on the northern slopes of Ventura and Los Angeles counties, is the result of a low-pressure system known as an inside slider that’s moving over the inland portion of the state.
Want to know when the next hot spell is coming? It might help to look at the weather forecasts — a few thousand miles away. Summer heat waves in California’s Central Valley are almost always preceded by heavy rainfall over the tropical Indian and Pacific oceans, scientists at UC Davis and in South Korea determined in a recently published research effort. Researchers identified 24 heat waves that took place in California’s Central Valley during summer months from 1979 to 2010, and compared those heat waves to a weather pattern called the Madden-Julian Oscillation (MJO) that brings heavy rain to the tropical Indian and Pacific oceans.
A series of storms this week in the Bay Area, including a weak ‘atmospheric river’ system Friday expected to bring widespread rain to the region, should allow San Francisco and San Jose to reach their annual rainfall totals. Since the start of the water year Oct. 1, San Francisco has received 23.27 inches of rain, just shy of its annual average of 23.65 inches. San Jose has received 14.82 inches (annual average is 14.90) and Oakland 18.57 inches (20.81 average).
There’s no weekend reprieve in store for Northern California after a wet start to the week. In fact, it should only get wetter. National Weather Service says Friday and Saturday will see a “stronger, wetter” storm than the one passing through Monday and Tuesday, with as much as 1 to 2 feet of snow possible near summit passes this weekend. Rain and snowfall were expected to be light during this week’s first storm, but Caltrans and sheriff’s departments have reported a snow slide incident Monday afternoon and an avalanche Tuesday morning, both of which closed stretches of highways.
Another powerful storm is expected to barrel into California later this week, but once again, San Diego should be on the southern fringe and get very little rain. In the meantime, mild weather is forecast for the workweek in San Diego County, with minor fluctuations in temperature and the reach of the low clouds. Up north, it’s a different story. An extremely wet storm, with seven times the amount of moisture usually seen this time of year, is expected to pound the Bay Area Thursday through Saturday with a couple inches of rain. National Weather Service forecaster Joe Dandrea said the Sierra could get 4 to 6 inches — a welcome, late-season addition to the state’s water supply after a subpar winter.
Imagine a river flowing through the sky – and all of its water dropping down to earth. That’s kind of what happens during many winter storms on the west coast. A so-called “atmospheric river” is a long, flowing band of water vapor – typically a few hundred miles wide – that contains vast amounts of moisture. When it moves inland over mountains, the moisture rises, causing it to cool and fall to earth as rain or snow. Duane Waliser of NASA’s Jet Propulsion Laboratory says atmospheric rivers are often beneficial, because they provide about half of California’s fresh water supply. But strong atmospheric river systems can also be dangerous – especially when they stall, or produce rain on top of snow.
Another round of soaking winter weather is on the horizon for the West Coast, with a series of storms expected to impact the region through midweek. Dry weather has been rare for much of California over the past week, with Sunday acting as a brief respite before more rain arrived overnight. “Unsettled weather will continue across the West Coast this week as more rain and mountain snow targets Northern California, Oregon and Washington,” according to AccuWeather Meteorologist Max Vido.
The heaviest rain, heaviest snow and highest probability of thunderstorms accompanying the current storm will pass through Northern California at varying times Wednesday. Early morning showers were scattered, dropping heavier precipitation in the northern half of the Sacramento Valley while Sacramento stayed mostly dry as of 6 a.m., as National Weather Service radar images show. Rain in Sacramento will likely begin later Wednesday morning.