Bay Area Logs Especially Wet May

In recent drought years, some sunny January days felt like summer. But this year, the opposite was true.

The region was soaked with the most May rain it has received in 21 years.

“The weather pattern literally looked like something straight out of January, but it’s May,” said Daniel Swain, a climate scientist with UCLA. “This regression back towards winter like conditions is amazing. There was a significant amount of rain near the coast.”

It was San Francisco’s 12th wettest May on record, according to the National Weather Service. The agency’s records show 2 inches of rainfall collected at San Francisco International Airport in May, the most since 1998, when 2.37 inches fell there.

The cause of all the rain is an unusually strong jet stream located farther south than normal, Swain said.  The rain is even stranger, Swain added, because the region’s long-term trend is towards drier springs. “This May really stands out as an outlier from that perspective,” he said.

After a rainier-than-normal winter, there was an abrupt end to the rainfall in March and virtually no rain in April. That’s a major reason why this year’s pollen season has been so tough for people with allergies.

Swain said the pollen season will likely last even longer this year after all the rain. June’s forecast shows warmer than average days  on the horizon as the beginning of summer approaches.

Allergy sufferers can find KQED’s pollen forecast here.