Not a drop in the sky all month

San Mateo County historically averages 4.06 inches of rain in February.   

The last measurable rain in the county was on Jan. 28 when just .03 inches were recorded, bringing rain totals that month to 1.18 inches compared to the historic January average of 4.19 inches.

At this point in the water year, which begins Oct. 1, the county on average gets a total of 14.49 inches of rain, but this year has seen just 6.19 inches of rain, which comes out to 43% of normal.

That’s not too far from rain totals during the recent drought between 2011 and 2017. At this point in the year in 2012, for example, the county received 5.68 inches of rain and in 2014 just 5.03 inches.

“It’s very unlikely at this point that we’ll catch up to normal for the whole season because we’re in so much of a deficit,” said meteorologist Spencer Tangen. “It’d have to be an extremely wet spring to make up for the dry winter.”

According to a report published last week by the U.S. Drought Monitor, 59.9% of the state is now classified as “abnormally dry,” up from 46.1% the week before. “Abnormally dry” in part means active wildfire season has begun.

The entire Bay Area and the counties that have experienced devastating wildfires in recent years are part of the “abnormally dry” areas while a portion of Central California is experiencing “moderate drought” conditions, according to the report.    

But that definition of drought, which speaks to changing weather conditions, is different from the definition of drought used by public water agencies, which takes into account hydrology and water storage in addition to weather, explained Nicole Sandkulla, CEO of the Bay Area Water Supply and Conservation Agency, or BAWSCA.

Using the latter definition, Sandkulla said California is not yet experiencing drought and new water conservation measures are not imminent.

“We’re not saying this is an official drought,” she said. “What we’ll do is review where we’re at the beginning of May when we get to the end of the rainy season and make an official call for this year and if it continues to be dry we’ll say use water efficiently and please conserve 10%, but nothing mandatory. It’s way too early for that.”

To reach normal levels this year, an additional 8.3 inches of rain would have to fall during spring. While weather conditions are almost impossible to predict more than a couple weeks into the future, the spring months of March, April and May collectively see an average of just 4 to 5 inches of rain historically.

The dry conditions are due to a ridge of high pressure over the Eastern Pacific that has effectively blocked all storms from coming into California since the end of January, Tangen explained, adding that the pattern is expected to continue into March.

“All storms have gone over the top of the ridge into the Pacific Northwest or Canada and a few are undercutting the ridge and going into Southern California,” he said. “It’s unfortunate the storms are all going around us. Hopefully we’ll see a pattern change and switch from high pressure to low pressure.”

The dry weather up north has caused the Sierra snowpack, which provides about one-third of the state’s water supply, to shrink dramatically since last year from 202% of normal to just 58% of normal, according to the National Weather Service.

An especially wet winter last year replenished the region’s water storage system, which is designed to withstand a six-year drought with the help of rationing, Sandkulla explained.

 “We’re in good shape going into this winter,” she said, adding that recent weather patterns are by no means good news, but also aren’t unheard of in California. “Dry periods are something we deal with in California so while this has been an exceptional February, it’s not unusual to have dry periods even in the middle of winter. But it doesn’t make me comfortable.”

zachary@smdailyjournal.com

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