Record Rainfall in Parts of Drought-Stricken California (RECAP)

Jon Erdman
Published: May 16,2015



 

After a winter and early spring yielding record low Sierra snowpack compounding a crippling multi-year drought, parts of California saw a strangely out-of-season soaking late this past week.
Record rainfall fell in southern California. On Thursday, showers and thunderstorms brought locally heavy rainfall to the San Diego area. San Diego International Airport measured 1.51 inches of rain in just about 90 minutes. A total of 1.63 inches fell on Thursday at Lindbergh Field, making it the wettest day in May on record.
This heavy rain brought flash flooding to the area with multiple water rescues reported. There was also a rain delay for the baseball game between the Washington Nationals at San Diego Padres on Thursday night. This is only the fifth rain delay at San Diego's Petco Park since opening in 2004.
San Diego is also experiencing its second wettest May as of Friday evening, with a monthly total of 2.35 inches. The current record for wettest May is 2.54 inches set in 1921.
Record rainfall also occurred in downtown Los Angeles on Thursday where a daily rainfall record of 0.69 inches of rain was set. LA broke the daily record rainfall again on Friday with an additional 0.16 inches. The previous record was only 0.03 inches set in 1902.

Satellite image and jet stream midday Thursday along the West Coast. Teal-shaded streamlines depict the strongest jet-stream level winds, illustrating the sharp southward plunge of the jet stream off the West Coast.

Pattern Change

You can thank the jet stream for this.
For much of this past winter and early spring, the polar jet stream had taken a large northward migration into Canada, keeping Pacific storms away from the West Coast.
Instead, late this past week, the jet took a sharp southward plunge over the eastern Pacific Ocean, steering vigorous upper-level disturbances into the West Coast.
While this precipitation may be considered "manna from heaven" in this sun-worshipping state, it is only a tiny drop in a massive bucket that is this multi-year drought.
Let's stick to the positive news, here. How unusual is this May rain?

How Rare is a May California Soaking?

January-April was the third driest such period on record in California, exceeded only by 2013 -- the state's record driest year -- and 1977.
From May through October, only 9 percent of the year's average rain fell in Los Angeles.
In May, that monthly average was a mere 0.26 inches of rain as the dry season started to set in.

Average rainfall in downtown Los Angeles in the wettest and driest six-month periods.

California drought monitor analysis from May 12, 2015. The darkest brown shading corresponds to the area of most exceptional drought.
(NOAA/USDA/NDMC)

You can understand state water managers completely throwing in the towel for the 2014-2015 water year by now.
However, L.A. picked up almost four times their average May rainfall in just a two-day time span this week (Thursday and Friday).
In fact, L.A. has only recorded 13 Mays since 1878 with at least an inch of rain, for an average return interval of once every 10-11 years. This last occurred in 2003.
In San Diego, this is even more unusual.
Only once since 1930 has this city synonymous with picture-perfect weather seen a one-inch rainfall in May -- May 8, 1977 -- when 1.49 inches was measured at Lindbergh Field.
Sierra snow isn't all that typical in May, either.
Tahoe City, California, only averages 2.3 inches of May snow. By this time of year, spring snowmelt of the heavy Sierra snowpack is well underway, replenishing the state's reservoirs, a prime source of drinking water.
Senior weather.com meteorologist Nick Wiltgen noted the winter storm warning issued for the Sierra earlier this week was the latest-in-season such warning by the National Weather Service in Sacramento since 2011.
To reiterate, this welcome May event is a tiny drop of drought relief.
(MORE: Strong El Nino Ahead?)
While often overstated and oversimplified to imply relief is certain, the developing El Nino may offer hope since the Pacific storm track may not be blocked from California as often next fall and winter, when the real wet season returns to a thirsty state.

MORE: California's Multi-Year Drought