Rainfall amounts so far this season have dropped to about 33 percent of average for early February throughout the Central Coast. Not only has it been mostly dry since our last significant rain on Jan. 9, but also warm.
In fact, temperatures in the previous week have averaged 10 degrees warmer than typical at the Santa Maria Public Airport, 15 degrees hotter at the Paso Robles Municipal Airport and nearly 20 degrees above record levels at the San Luis Obispo County Municipal Airport. Since Jan. 28, eight daily high temperature records between these Central Coast airports have been recorded.
The combination of lack of rainfall and well-above normal temperatures has driven most of San Luis Obispo County into a D1 (moderate drought) condition and Santa Barbara, Ventura and Los Angeles counties into D2 (severe drought), according to the United States Drought Monitor.
So what has occurred to produce this dry and warm weather pattern? It appears that the “Ridiculously Resilient Ridge of High Pressure,” made famous by the previous drought, has redeveloped over California. Not only has this high-pressure ridge kept California dry but also has produced persistent northeasterly (aka Santa Lucia/offshore along the Central Coast) winds. Lately, we haven’t even seen the marine layer develop along the beaches due to this offshore flow.
The current La Nina condition is wrapping itself around the equator.
“The presence of a mild La Nina, the notorious ‘Diva of Drought’ present at the equator, doesn’t bode well for winter rainfall,” said climatologist Bill Patzert at NASA’s Jet Propulsion Laboratory. To make matters worse, the Pacific Decadal Oscillation (PDO) has turned neutral.
So why is this year's La Nina different from last year's, which produced record amounts of precipitation in Northern California and well-above typical rainfall along much of the Central Coast?
During the 2017 (July 1, 2016, through June 30, 2017) rainfall season, the PDO was positive. More importantly, there was a tremendous amount of warm water left over from the 2015-16 El Nino in the western tropical Pacific near Malaysia and to a lesser extent in the far eastern Pacific. If you remember, the 2015-16 El Nino events, one of the strongest ever seen, and many oceanographers would say it was the warmest. This condition caused the Variable Pacific Jetstream or the Southern Branch of the Polar Jetstream to shift southward toward California, which brought one storm after another last year. This year, the reinvents of the Godzilla El Nino have dissipated into the depths of the Pacific.
Another cause that continues to gain interest was put forth several years ago by Dr. Jennifer Francis, of Rutgers University. She hypothesizes that Arctic Amplification (the Arctic is warming at a quicker rate than the rest of the Earth) will increase the amplitude of jet stream waves. In other words, the upper-level winds are more likely to travel in a more north to a south pattern. You see, the polar jet stream often forms the border between the frigid air to the north and the warmer air to the south. As a rule of thumb, the higher the temperature differential between these two air masses the faster the upper-level winds will blow. The faster the jet stream, the more direct route it takes. The slower the jet stream, the more likely it will tend to change direction.
In California, the most advantageous pattern is for the upper-level winds to travel in a direct path across the Pacific to the coast; as the mid-latitude westerly winds increase the higher the likelihood of rain. Lately, the jet stream hasn’t had enough momentum (speed) to break through this ridge of high pressure and allowed the mid-latitude westerly winds to carry storms to the Central Coast. On a positive note, the long-range models continue to advertise the possibility of periods of rain starting around Valentine's Day and continuing through the end of the month. Of course, March can also produce massive amounts of rain, as evident by our Miracle March in 1991 and the floods of 1995.
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I will be with spatula on Valentine's Day, Feb. 14, to help raise funds for water wells in developing nations with food by Popolo Catering. The Well Worth It Campaign, launched by Cannon in 2010, will host a pancake breakfast fundraiser at its office, 1050 Southwood Drive, San Luis Obispo, from 7 to 8:30 a.m. Access to clean water remains an issue in many parts of the world. The Well Worth It Campaign has raised enough money to fund the construction of over 20 wells worldwide. Those wells help eliminate water-related illnesses, which are a severe health issue. For a $10 donation during the Fifth Annual Pancake Breakfast, you can enjoy unlimited pancakes, eggs, sausage, OJ and coffee (kids eat free with each paid adult). You won’t want to miss the special treat: chocolate chip pancakes!