SLO County saw above-average rainfall this month. Was it a Miracle March?

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 United States Drought Monitor. Much of San Luis Obispo County and all of Santa Barbara and Ventura counties were listed as D1 (Moderate Drought) level.

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

Typically, we receive about 3.20 inches of rain in San Luis Obispo, 2.50 in Paso Robles, and 2.60 inches in Santa Maria during March.

This March, Cal Poly in San Luis Obispo recorded around 6 inches of rain, while the Santa Maria Public Airport saw nearly 4 inches. Paso Robles Municipal Airport reported more than 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 rainfall by the end of this month.

This well-above-average rainfall dropped the drought level from D1 (Moderate Drought) category 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 the one we saw in 1991, but perhaps a “Mini Miracle March” as the snowpack in the Sierra Nevada has significantly increased but still remains lower than average.

However, we are all grateful for the extra moisture — 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.

This condition frequently weakens cold fronts as they head down the California coastline, which diminishes the strength of the pre-frontal (southerly) winds but tends to increase the post-frontal (northwesterly) winds.

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

The longer days produce warmer temperatures in the inland valleys.

As the valley’s surface air is warmed, it expands and rises like a hot air balloon. This, in turn, produces lower pressure at the earth’s surface.

Meteorologists refer to this as a thermal low. Nature never likes anything out of balance, and consequently, the higher air pressure out over the ocean forces air inland in to fill the void left by the thermal low.

These northwesterly winds will also affect our seawater temperatures.

In March, 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 March, seawater temperatures have ranged between 57 and 59 degrees Fahrenheit at the Diablo Canyon Power Plant’s marina — much warmer than typical at this time of the year.

However, that’s about to change, and here’s why.

As these northwesterly winds blew 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 and nutrient-rich subsurface water ascends to the surface along the beaches.

At times like these, seawater temperatures can plummet to a bone-chilling 48 degrees!

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

PG&E responds to coronavirus

PG&E delivered a donation of nearly 1 million safety masks amid the COVID-19 pandemic on March 22 to the Governor’s Office of Emergency Services. To lean more, please visit www.pgecurrents.com