This month has been among the driest, warmest Marches on record across much of California, but a storm system moving through the state this week is expected to bring a modest amount of rain in the month’s final days.
As of Monday, a National Weather Service station in downtown San Francisco had recorded 0.06 inches of rain for the month, just above the record low for March of 0.03 inches, set in 1923. Across the greater Bay Area, rainfall totals have ranged from zero to around 0.20 inches — more than two inches below normal for the month, according to the National Oceanic and Atmospheric Administration.
Farther south, conditions have been even drier. There has yet to be any measurable rain recorded this month in downtown Los Angeles. The last time March passed without measurable rainfall there was 1997, and before that, 1959. Other notably dry Marches included years with only a trace of rainfall, such as 1972, 1956 and 1931, while just 0.01 inches was recorded in 2008, 1934, 1932 and 1885.
It has also been one of the warmest Marches on record. A heat wave this month pushed temperatures across much of the West 3 to 9 degrees Fahrenheit above average, according to the Climate Prediction Center, resulting in numerous daily and monthly record-highs across California.
In the Los Angeles region, 75 daily temperature records were broken, and 10 locations set new March records. At Long Beach Airport, the temperature reached 99 degrees on March 17, surpassing the previous record of 98 degrees that was set twice in March 1988. Burbank Airport also saw temperatures in March hit 99 degrees, exceeding its previous record of 98 degrees. In the greater Los Angeles area, Woodland Hills notched a high of 102 degrees, beating its top March reading of 98, also set in 1988.
The Bay Area saw similar extremes, with at least nine stations recording new highs for March. In San Francisco, temperatures hit 90 degrees on March 20, the first time the station there had ever recorded 90 degrees in March, an unusual temperature even for the height of summer. The previous record for the month was set in 2005, at 87 degrees.
Where the rain is expected.
A weather system that is expected to move across California is forecast to bring light rain to parts of the state between Tuesday and Thursday morning.
The heaviest rain is expected in the northern part of the state, where the Eureka office of the Weather Service forecasts two waves of rainfall. The first, from Monday through Tuesday, should bring lighter totals of up to 0.50 inches. The second, arriving Wednesday afternoon, is forecast to deliver more widespread rain, including a period of moderate to heavy rain along the North Coast.
In the King Range and in the mountains of Del Norte and northern Humboldt counties, totals could reach from 1.5 to 2.5 inches. Most of the rain will be beneficial there, where some places have been classified as “abnormally dry” by the U.S. Drought Monitor. But forecasters warned it could also lead to minor flooding, slick roads, rockslides and reduced visibility.
Most interior parts of the San Francisco Bay Area are likely to see 0.10 inches of rain or less, while coastal mountains could receive up to 0.25 inches. In the Los Angeles region, rainfall totals are expected to remain light as well, with 0.10 inches or less forecast.
Snow is also expected in the higher elevations of Northern California. In the northwestern part of the state, totals could range from around two to six inches, particularly over Scott Mountain Pass on Wednesday. Light snow may also fall over the highest passes. Farther inland, the greatest snowfall accumulations are expected near the highest peaks of the southern Cascades and the northern Sierra Nevada, where around four to six inches of snow could fall, mainly above 6,000 feet.
The cooler, wetter weather won’t last.
California’s snowpack, a critical water resource in the warmer months, was already below average after an unusually warm and dry winter. As of Monday, the statewide snowpack sat at roughly 18 percent of its normal level.
The snowpack in California’s mountains typically supplies about a third of the state’s water. But officials said the unusually warm temperatures in March accelerated the annual melting of the snowpack, much of which was already reduced after a warm storm in late February brought rain instead of snow to the highest peaks of the Sierra.
The rain and snow this week are expected to be short lived. By Friday, forecasters said a high pressure system was expected to move into the region, bringing a return to drier conditions and possibly warmer weather heading into the end of the week.
In the long term, officials are concerned for drought conditions later this spring. According to Brad Pugh, a meteorologist with NOAA, the below-normal precipitation, the low snowpack — combined with the early melt of what snow had accumulated — and the record heat in March could lead to expanding drought conditions as early as April across much of the Western United States.
Nazaneen Ghaffar is a Times reporter on the Weather team.
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