February brought county a big chill

Alexander Kunz moved to San Diego County from Germany in October 2010. He quickly became spoiled by Southern California weather.

“I remember hiking in February in shorts — and sweating,” Kunz said.

Not this year.

Kunz ran his heater at his home in Rancho Bernardo more in February than ever, sometimes day and night. Frost blackened the leaves of the bougainvillea in the front yard, and hail gathered in patches one day in his backyard.

On Feb. 22, Kunz, a professional photographer, drove out to Lake Henshaw to shoot one of his favorite scenes in the county.

“I went out wearing two pairs of pants,” he said. And he shivered. It was 26 degrees.

For much of San Diego city, it was a throwback February — a return to the chilly winter weather that hadn’t been seen in years but used to occur fairly regularly. San Diego ended the month 2.2 degrees cooler than normal, with both nights and days chillier than usual. But you only have to go back to 2008 to find a February just as cold.

Inland, however, February was bone-chilling and record-breaking cold. Final numbers aren’t in yet, but even with a slight warmup the last few days of the month, it appears Ramona had its coldest February on record, and Palomar Mountain, Vista and Campo all had their second coldest.

Greg Bowerman, who has lived in Pine Valley since 2001, can confirm. His personal weather station showed temperatures dropping into the teens six days during February. Normally, he said, he sees one or two days that cold in an entire year.

“I’m going through firewood like never before,” he said.

It was a kind of hybrid February, with a combination of weather elements rarely seen. Besides the cold, there was plenty of rain (most places received at least 150 percent of normal), low-elevation snow, a couple of very moist “atmospheric rivers” and a little bit of El Niño.

Add them up and you get an odd kind of perfect storm that was hard to foresee and decipher.

“Two things stand out,” said Alex Tardy, a meteorologist at the National Weather Service’s Rancho Bernardo office. “We had those atmospheric rivers, which typically don’t affect temperatures. They usually keep us mild. Then we had four outbreaks of our version of the polar vortex over Southern California.”

Cold storms with origins in Alaska or Canada usually descend on Southern California four or fives times an entire winter, Tardy said. Some winters don’t deliver any. San Diego County got four in one month.

Frost was widespread around the county Feb. 6 and 7, then again over several days between Feb. 18 and 23. San Diego had 14 days with lows in the 40s, and only one day topped 70 degrees all month.

Many winters, the county will get no atmospheric rivers, let alone two in one month. The rivers are long plumes of moisture a couple of hundred miles wide that can stretch out into the Pacific for a thousand miles or more. They can dump huge quantities of rain over a region.

Although neither river took direct aim at San Diego, the river on Valentine’s Day drew a bead on Palomar Mountain, which set its all-time, single-day rainfall record with 10.1 inches.

A week later, Palomar Mountain was blanketed in snow. That snow cover helped keep temperatures down on the mountain both day and night, Tardy said.

But in Vista, Ramona and Campo, snow cover had nothing to do with the chill. The month’s many storms were remarkably cold, and for the most part, they cleared out at night and left cold air behind.

“To get those really cold night temperatures, you have to have clear skies,” Tardy said.

Then there’s El Niño, the periodic atmospheric phenomenon that alters storm patterns around the globe and often delivers extra rain to Southern California. The Climate Prediction Center had been touting El Nño’s emergence for months, but it didn’t officially arrive until the middle of February.

“I think there’s been a mild influence of El Niño, at best,” said Dan Cayan, a climate researcher at the Scripps Institution of Oceanography. “The precipitation pattern is sort of the classic El Niño signature, with lots of rain in California and drier in the Northwest. But the circulation pattern doesn’t really look like El Niño. And El Niños have tended to be warmer in the West.”

The cold in February came after an unusually long stretch of warm weather. Since October 2013, a span of 63 months, San Diego had only one month cooler than normal: May of last year. And that month was just 0.5 of degree below normal. During that five-plus-year stretch, San Diego had its two hottest years on record and many months that set all-time heat records.

What changed in February, the first month to be more than 2 degrees cooler than normal since August of 2011?

“All of the sudden we’ve had this abrupt shift in the circulation,” Cayan said.

High pressure had dominated along the West Coast most of the last several years. Now a trough of low pressure rules the region, and that has allowed influxes of cold air from the north. Also, ocean temperatures along the West Coast that had been much warmer than normal returned to closer to their historic averages.

Cayan notes that it’s not as if cold has descended everywhere.

“There’s been a kind of redeployment of the air masses,” Cayan said. “If you charted the area of cold air masses and warm air masses, you’d find an equal amount of warm as cold.” Now unusual warmth can be found up in Alaska and the Southeast.

What’s next? The stormy local pattern, which actually goes back to early December, is not going away soon. Rain is expected over the weekend, and two more storms are forecast for next week. No heat waves are on the horizon.

Bowerman out in Pine Valley says the creek that flows under his driveway has already reached the highest level he’s seen since he’s lived there. Around the county, streams are flowing, vernal pools have filled and hillsides have greened up. The desert and backcountry appear primed for a delayed but prolific bloom season.

“We have not had a winter with this combination of cold and wet in a long time,” the weather service’s Tardy said. “We should see very good native plant growth this spring and summer. It should be one of the best springs we’ve had in a long time.”

rob.krier@sduniontribune.com

(619) 293-2241

Twitter: @sdutKrier

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