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John Lindsey: March rains lift area from drought to dry

John Lindsey: March rains lift area from drought to dry

Rain, south of San Luis Obispo

Wolfgang Kaml took this photo of an “incredible sunset with the rainstorm moving across the grade” Thursday.

As a mostly dry January turned into a record-dry February — the heart of our rainfall season, which runs from July 1 to June 30 each year — precipitation amounts dropped to about a third of average throughout the Central Coast.

The lack of moisture in February drove most of California from the D0 abnormally dry to D1 moderate drought category by early March, according to the weekly U.S. Drought Monitor.

All of Santa Barbara and Ventura and much of San Luis Obispo counties were listed at D1 moderate drought level.

However, earlier this month, the Eastern Pacific high shifted into the Gulf of Alaska, which opened the storm door to the Central Coast, and our weather pattern changed drastically as a series of storms swept through our area and brought much-needed rain.

Typically, we receive about 2.6 inches of rain in Santa Maria, 3.2 inches in San Luis Obispo and 2.5 inches in Paso Robles during March.

This March, Cal Poly — home of climatology for San Luis Obispo — recorded around 6 inches of rain, while the Santa Maria Public Airport saw nearly 4 inches and Paso Robles Municipal Airport reported over 3 inches.

Overall, most Central Coast locations went from about a third of average rainfall at the beginning of March to one-half to two-thirds of typical by the end of the month.

That well-above-average rainfall in March dropped the drought level from D1 moderate drought to the D0 abnormally dry level, the lowest grade of drought, throughout the Central Coast.

I probably wouldn’t classify this month as a “Miracle March” like 1991, but perhaps a “Mimi Miracle March,” as the snowpack in the Sierra Nevada has significantly increased but still remains lower than average.

However, we are all grateful, especially our ranchers and farmers.

Looking forward, the northwesterly onshore winds of spring will return along the Central Coast.

Spring is a transition season in terms of weather conditions: not quite summer and not quite winter. At this time of the year, the Eastern Pacific high off the California coast strengthens and gradually shifts northward.

That condition frequently weakens cold fronts as they head down the California coastline, which diminishes the strength of the prefrontal southerly winds but tends to increase the postfrontal northwesterly winds.

The northwesterly winds of spring are further enhanced by the higher amount of sunlight as the days grow longer.

Let me explain: The longer days produce warmer temperatures in the inland valleys. As the valleys’ surface air is warmed, it expands and rises like a hot air balloon. That, in turn, produces lower pressure at the Earth’s surface. Meteorologists refer to that as a thermal low. Nature never likes anything out of balance, so consequently, the higher air pressure out over the ocean forces air inland in to fill the void left by the thermal low.

Those northwesterly winds will also affect our seawater temperatures.

This month, persistent southerly winds produced a northerly “Davidson” flowing current, which brought a warmer body of seawater to our coastline from the south. Also, the lack of northwesterly winds resulted in very little upwelling.

This month, seawater temperatures have ranged between 57 and 59 degrees at the Diablo Canyon Power Plant Marina, much warmer than typical at this time of the year. However, that’s about to change, and here’s why:

As the northwesterly winds blow along the coastline, the friction of the wind causes the ocean surface water to move.

The apparent Coriolis force turns the surface water to the right, or offshore, causing upwelling along the shoreline as very cold, nutrient-rich subsurface water ascends to the surface along the beaches.

At times like that, seawater temperatures can plummet to a bone-chilling 48 degrees.

As the winds blow across the cold seas, they are cooled like a gigantic air conditioner. Not only are the winds cold but, thankfully, they are also almost free of pollen along the coastline.

***

Pacific Gas and Electric Co. delivered a donation of nearly 1 million safety masks to the Governor’s Office of Emergency Services on March 22 amid the COVID-19 pandemic.

To lean more, visit www.pgecurrents.com/.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter @PGE_John.

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