Weather Watch

High temperatures broke records countywide in May

Hay bales in a field on Los Osos Valley Road. The dry conditions illustrate the low rainfall and high temperatures in May.
Hay bales in a field on Los Osos Valley Road. The dry conditions illustrate the low rainfall and high temperatures in May.

It will probably come as no surprise that this May was one of the warmest on record throughout San Luis Obispo County. Take a look at the numbers:

San Luis Obispo County Regional Airport averaged 64.8 degrees, whereas the usual average in May is 57.9 degrees.

Historically, the airport averages less than one day with maximum temperatures over 90 degrees in May. This May, however, five days exceeded that maximum, including two record-breaking days with temperatures reaching or exceeding 100 degrees.

In the North County, where Paso Robles County Airport normally averages 62.9 degrees in May, this May averaged 68.1 degrees, nearly breaking the 1997 all-time record of 71.9 degrees.

On average, Paso Robles has about six days of temperatures breaking the 90 degrees mark in May. This May, Paso Robles experienced 14 days of temperatures above 90 degrees and three days over 100 degrees.

The beaches experienced a nearly fog-free month, and Baywood Park in Los Osos hit 103 degrees on May 14.

The end of this month will mark the end of the 2013-2014 California rain season, which runs from July 1 through June 30. Unless we receive some kind of miracle June rainfall, Paso Robles will break its record for least seasonal rainfall.

So far, only 3.34 inches have been recorded in Paso Robles, breaking the 2007-2008 rain season’s record low of 4.2 inches.

The tipping bucket rain gauge at the Diablo Canyon Power Plant meteorological tower has recorded only 5.76 inches of precipitation, smashing the previous record of 7.89 inches set in the 1989-1990 rain season.

Cal Poly has recorded 10.61 inches this rain season, whereas it normally records over 22 inches.

This is the ninth driest rain season on record, the first driest being the 1897-1898 rain season when only 7.20 inches were recorded.

While the numbers are sobering, they don’t tell the full story. Unfortunately, this season was the third consecutive dry rain season. In fact, this has been the second driest three-year period on record at Cal Poly, recording a total of 39.56 inches of rain.

The first driest three-year period occurred from 1958 through 1960, during which only 38.80 inches of rain fell. No other three-year period is near these two.

The drought monitor map issued by the National Drought Mitigation Center indicates that most of California has moved into the extreme drought category. The worst category, “exceptional drought,” stretches across the entire Central Coast, encompassing all of Monterey, San Luis Obispo and Santa Barbara counties.

As the state heads into summer, the latest forecast from the U.S. Climate Prediction Center (CPC) predicted “above normal temperatures” for all of California through August and worsening drought conditions.

But not all the news is bad. The CPC is still indicating increasing chances for a moderate to strong El Niño event developing later this year — but keep in mind, historical rainfall data indicates no guarantee of drought-breaking rainfall in California during an El Niño.

In truth, weak and moderate El Niño events don’t seem to have much effect along the Central Coast. However, strong El Niño events on average produce about 140 percent of normal precipitation here.

Historically at Cal Poly, there has never been a period of four straight years of well-below normal precipitation. In my humble opinion, the 2014-2015 rainfall season could be very different than the last three we’ve experienced.

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