Warm spell hits 100 days - and counting

Streak fits with rest of toasty 2014

By Robert Krier8:19 A.M.AUG. 17, 2014
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Large thunderclouds produced localized showers in the east county of San Diego Tuesday from Campo to Mount Laguna and then the desert before departing. These monsoon rainclouds are typical of the month of August in San Diego County. — John Gastaldo



Call it San Diego’s 100 Days of Simmer.
Sunday was the city’s 100th straight day with warmer-than-normal temperatures. It’s a rare streak, the longest for San Diego in 30 years and the fourth-longest in city history.

The temperature pendulum has stopped swinging, and that has implications for backyards, energy use, even sleep patterns.

The streak fits with the rest of 2014, which has been one of the city’s warmest — and driest — years on record.

First, an explanation.

The National Weather Service calculates the average temperature for a day by adding the high and the low, then dividing by two.

For example, if the high were 80 degrees and the low 70, the day’s average would be 75. That 75 is then compared with the climatological average for the date.

Since May 9, which was exactly at the average mark, every day has been at least one degree warmer than the climatological average. In the past five years, the longest similar streak was 45 days. Usually, temperatures fluctuate between above normal and below normal every few days or weeks.

Which is not to say that every day during this current streak has been blazing hot. Other than a scorching, record-breaking five-day stretch in mid-May — at the time of several wildfires — and a three-day spell in early July, many of San Diego’s daytime highs have actually been fairly pleasant and near normal.

The one constant during the 100-day run? The nighttime lows have persistently been above normal. Only one day (June 19) didn’t have a low temperature that was above normal.

Through Saturday night, there had been 19 nights that never dipped below 70 degrees since early July. (The normal low temperature is 64 degrees in early July and 67 in mid-August.)

The nighttime warmth has caused many people to turn on their fans or air-conditioning systems when they get home from work — and then leave them on longer than they usually would.

San Diego Gas & Electric customers used 5 percent more energy from 5 p.m. to 10 p.m. from May through July this year than they did during the same period in 2013, SDG&E spokeswoman Erin Coller said. Energy use for all hours during the period this year was up by 3 percent.

The sultry nights also affect sleep. Researchers know that the ideal temperature range for sleeping varies widely among individuals. People used to sleeping in a house in the 60-degree range, however, can find it harder to fall asleep and stay in Dreamland when the temperature doesn’t dip below the low 70s.

Why the warmth?
Meteorologists point to a few factors that may be contributing to the uninterrupted stretch of above-normal temperatures.

For much of the 100 days, the ocean temperature off San Diego’s coast has been warmer than usual.

“Warmer water raises the baseline of how low our average temperature can go around here,” said Miguel Miller, a forecaster for the National Weather Service in Rancho Bernardo.

Warmer water reduces the contrast between the air and water, which makes the formation of cooling low clouds less likely.

“Also, we’ve had a pretty decent amount of high pressure over the area, and monsoonal flow. These things tend to keep us above normal,” said Ivory Small, science officer for the weather service.

During a monsoonal flow, warm, moist air from the east, south or southeast moves over the San Diego region. The effect appears off and on every summer, but it has been a more frequent visitor than usual this year, and it has often pushed farther west. In many summers, only the county’s mountains and deserts see the monsoon’s impacts.

More of the same
The late-spring and summer run of warmer weather is just an unbroken extension of what has been going on all year. Since Jan. 1, San Diego has had only nine days that were exactly normal, only eight days that were cooler than normal and 213 that were warmer than normal.

Every month of 2014, plus the first half of August, has been warmer than average. The first six months of the year were the warmest January-through-June period in city history. Temperature records in town go back to 1872.

All that warmth has affected what’s growing — and crawling — in backyards.

“Insects are cold-blooded,” said Vincent Lazaneo, urban horticulture adviser emeritus for the UC Cooperative Extension.

“The warmer the temperature, the faster their life cycle.”

Lazaneo said many gardeners are being hammered by pests like the tomato psyllid, an aphid-sized insect that was able to survive the winter in many yards because of a lack of cold nights. Also, many fruit trees that require cool winter nights for a bountiful crop are producing poorly this year.

Last but not least, the warm spell has had an obvious impact on the drought. Despite admonitions from the governor and various water agencies to conserve, water use in most areas of California — including San Diego — went up during the first half of the year.

“People are trying to keep their landscapes alive,” Lazaneo said.

Historical comparison
This current 100-day stretch still has a long way to go to catch up with 1984, San Diego’s warmest summer — and year — on record.

In ’84, the city went 168 straight days with above-average temperatures. Daily records for highest minimum temperature were set on 53 days from July through September of that year, including the two warmest nights in city history: 78 degrees on Sept. 9 and 17.

Small recalls that summer well.

"I remember seeing a lot of tropical sorts of influences moving into the area," he said. "I lived in the dorms at UCLA, and we had no air conditioning."

How long will the latest streak last? The forecast shows no sign of it ending soon, largely because the lows are expected to continue being a few degrees above normal.

If the streak lasts two more weeks, it will move into third place in San Diego history. If it lasts three weeks, it will become the second longest.

“It doesn’t want to quit,” Small said.

rob.krier@utsandiego.com • (619) 293-2241 • Twitter: @sdutKrier

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