Not good news for us here in San Diego: From the San Diego Union Tribune April 21st, 2018
San Diego has been exceptionally dry this year. Storm after storm has avoided or barely brushed the region.
Will this go down as the driest year in city history?
It’s a real possibility, although a bit of a longshot. The city has been this dry so late in the season only one other time since 1850, when rainfall records began in town.
The odds of breaking the dryness record are long, because there are still more than five months left in the season. But stranger things have happened.
Given the current rain-robbing, storm-deflecting weather pattern that stretches back 10 months and the city’s rainfall history, this could be the year when the longshot comes in.
The vast majority of the years, by this time, San Diego has already blown way past 3.33 inches of rain, the total in 2001-02, the record dry year. Average rainfall through April 30 is 9.95 inches; average for the entire rainfall year, which ends Sept. 30, is 10.34 inches.
This year, the season total after Thursday’s brief morning shower is just 3.19 inches. Only 2001-02, with 3.02 inches at the end of April, was drier.
To break the dryness record, the city would have to get no more than 0.13 of an inch of rain between now and the end of September.
Could it happen? There’s precedent. Seven times the rainfall total during that stretch was that low or even lower.
Three times the city has gone at least 164 days, starting in April and continuing the entire summer, without any rain at all. The city’s longest dry spell, 182 days, began on April 17, 2004, and it didn’t end until Oct. 16 that year.
The Climate Prediction Center, which makes long-range forecasts, sees no tilt toward either dry nor wet for Southern California as the summer approaches. But San Diego’s averages during the summer months are virtually zero, said Mike Halpert, the center’s deputy director.
Under El Niño conditions, when the waters in the equatorial Pacific turn abnormally warm, the chances of San Diego getting summer rain from the remnants of a tropical storm off the west coast of Mexico increase. But the prediction center doesn’t expect El Niño to emerge over the summer, Halpert said.
For the shorter term, through the next 10 days or so, no storms are on the horizon.
Annual dry run
San Diego is on the cusp of its annual, long dry stretch, which often starts in late spring and lasts until early fall. April is the transition month. Storms from the north usually still arrive, but they are generally less frequent and weaker.
Until last Thursday, San Diego had recorded no rain at all in April. Thursday’s total was just 0.01 of an inch.
The dry pattern emerged last year. San Diego had its driest June-through-December period on record. January and early March brought some rain, but both were drier than normal.
In late March, it went back to extremely dry, at least locally.
San Diego was initially forecast to be on the southern fringe of strong storm systems hitting California, but eventually the city missed out on even the fringe. A couple of “atmospheric rivers,” long plumes of moisture a couple of hundred miles wide and more than a thousand miles long, drenched areas to the north but left San Diego alone.
“With the last couple of atmospheric rivers, the long-range forecasts looked promising,” National Weather Service forecaster Mark Moede said. “But with each succeeding forecast model run, the rivers shifted farther north.
“We had been hyping it (the last atmospheric river) days in advance, and it ended up being a non-event.”
What caused those plumes of moisture to stay far from San Diego is the question.
In the normal weather pattern, a ridge of high pressure in the eastern Pacific, roughly west of the southern tip of Baja California, waxes and wanes as storms drop down from the north Pacific and move east across the continent.
This year, it appears that subtropical high amplified, Moede said, and that could have helped repel the storms from Southern California.
The last two weeks, a series of storms, weaker than the ones that soaked California in March, continued to deliver more rain and mountain snow in Northern California. Again, San Diego remained on the outside looking in.
Making it through April with very little rain is key to breaking the record. After April, which averages 0.78 of an inch in San Diego, the monthly rainfall averages drop way off. And those small averages are inflated by the rare, wet month.
About a third of the years, May has recorded 0.04 of an inch or less. In June, about three-fourths of years had 0.04 or less. Most of the city’s Julys, Augusts and Septembers have recorded no rain at all.
September can catch early winter storms, but only one September in the last 13 years recorded more than a tenth of inch of rain.
The Climate Prediction Center’s Halpert said it’s not too hard to break daily records for temperature or rainfall, but topping a record for an entire year is difficult. Even with the current dry trends and past long dry stretches, the odds are long that San Diego’s will break the dryness record this year.
And writing about it will likely jinx it.
“This story is the kiss of death,” Halpert said. “The record probably won’t happen now.”