What the Weekend Rains Did to Southern California—and What a Real Hurricane Could Do
By: Bob Henson , 3:07 PM GMT on July 21, 2015
The maxim “be careful what you wish for” comes to mind when pondering last weekend’s amazing rain across Southern California. After three years of fierce drought, some of the heaviest midsummer rains on record struck the region, facilitated by the remnants of former Hurricane Dolores. The spirit-boosting effects of the rain were accompanied by some [url=]rare disruptions[/url], including a bridge collapse along Interstate 10 in far southeast California and the first rained-out pro baseball game at Anaheim’s Angel Stadium since 1995. As unusual as the rain was, there could be even more to come in the next several months, as an already-strong El Niño event continues to gather steam. Records for Southern California from the past century show that the risk of impact from Pacific tropical storms and hurricanes is greater during El Niño years. History also tells us that we can’t rule out the possibility of a full-blown hurricane coming ashore: this apparently happened in 1858, long before the region was densely populated.
Figure 1. Emergency crews respond after a pickup truck crashed into the collapse of an elevated section of Interstate 10 on Sunday, July 19, 2015, in Desert Center, Calif. The bridge, which carries the eastbound interstate about 15 feet above a normally dry wash, snapped and ended up in the flooding water below, the California Highway Patrol said, blocking all traffic headed toward Arizona. Image credit: Chief Geoff Pemberton/CAL FIRE/Riverside County Fire, via AP.
A century’s worth of July rain in one weekend
As the circulation around ex-hurricane Dolores stalled southwest of San Diego over the weekend (see Figure 3), the flow around it contributed to a channel of rich moisture flowing northward across much of Arizona and Southern California. Dewpoints rose to sultry Southern levels as high as the upper 60s in Los Angeles and the low 70s in San Diego. Very light rain had been in the forecast along the southern CA coast, but the amount of instability proved greater than expected, and intense thunderstorms developed on Saturday afternoon and evening. Much of western San Diego County picked up an inch or more of rain on Saturday, with another 0.50” – 1.00” widespread on Sunday and some lighter amounts on Monday. San Diego’s Lindbergh Field measured a whopping 1.69” on Saturday and Sunday—more rain than in any other July in San Diego records that go back to 1850 (the runner-up was 1.29” in July 1865). Midsummer is typically bone-dry in San Diego, with June through August racking up a combined average of just 0.14”. Amazingly, the past weekend produced more rain in San Diego than the previous 100 Julys combined (1915 – 2014). This was also more rain than the year’s wet-season months of January, February, and March managed to cough up. Downtown Los Angeles notched 0.38” over the weekend, its greatest monthly total for any July in records going back to 1877 (the previous record was 0.24” in July 1886). In that entire 139-year period, the station recorded a total of 1.17” of July rain, with close to a third of it falling this year....
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