March storms give BIG boost to California's water supply
Thursday, March 29, 2018, 21:00 - The Atmospheric River that affected large portions of California between March 20 and 23rd brought significant amounts of precipitation to the state. The 3-day precipitation event was reinforced by a steady and impressive injection of moisture from the southwest, a Pineapple Express that was especially efficient across a large portion of Central California.
The Atmospheric River event in Numbers
Moderate to heavy precipitation was reported over central and southern California for about 72 hours. The highest precipitation amounts occurred along the windward slopes of the central coastal ranges with several thunderstorms forming and enhancing precipitation between March 22 and March 23rd.
Image courtesy of NOAA. NOAA Precipitation Summary
More than 10 inches where measured in the higher elevations of Big Sur and the southern Sierra Nevada´s. Further south, Thomas Fire affected areas in Santa Barbara and Ventura counties where able to soak in 5 to 6 inches of rain without suffering major flooding or landslide events. The Los Angeles Basin and higher elevation terrain of San Diego and Orange counties received anywhere from 0.75 to 3.9 inches. This Atmospheric River event produced nearly 7% of the normal annual precipitation over all of California. The largest 3-day precipitation accumulation of 10.24 inches was measured at the Three Peaks over Big Sur.
Comparison with all heavy precipitation years from CWWE
Rainfall Intensity Categories from CWWE
A considerable increase in the seasonal rainfall was noted across many California observatories after the Atmospheric River event took place. Paso Robles in central California boosted its rainfall totals for the season from a low 48% of normal to 86%. Even downtown Los Angeles got away with a 9% increase.
In Sacramento rainfall this water year has altered between dry and wet. The month of March however, has become the wettest March of all time for downtown Sacramento.
California Water Year Precipitation Update
Snowpack below average in the Sierra Nevada's but looking healthier
Despite being a warmer storm and with snow falling at higher elevations, March 27th data shows that snowpack increased across some areas of the Sierra Nevada´s. It is higher in the Central Sierra than in the northern and southern sections of the range, with 65% of normal for the date. Overall the statewide average is at 58%, a considerable increase with respect to values measured earlier in the month.
Regional snowpack as of March 29
Snow water content is still below average in all 3 monitored sectors of the Sierra Nevada's, but has shown a steady increase since mid-February. There is also a steep upward trend following the recent Atmospheric River event especially in the central and southern Sierra. It is especially great to see, that despite initially following the trend reported during the very dry 2014-15 season, the 2017-18 season has now shown signs of recovery, although the peak of the season is coming to an end, and in in no time the Precipitation season will come to an end.
Atmospheric River takes a bite at California Drought
Drought monitor maps updated this Thursday, March 29th show how overall California drought has been reduced. It still extends across much of the state, especially the southern half, but the extreme drought situation which affected portions of the Los Angeles basin is now only confined to the extreme southeast counties of the state.
Drought outlook as of March 29 c/o U.S. Drought Monitor
Despite the heavy rain collected in late March, severe drought does however persist from San Luis Obispo southward into most of the Los Angeles basin, but the area has shrunk considerably. Moderate drought continues to dominate across a large swath of the rest of the state, but it has been replaced in ample areas where just a week ago severe drought conditions where the norm.