This year’s abnormally warm waters in the Eastern Pacific — caused in part by an El Niño that continues to strengthen — has helped to produce more tropical cyclones than usual in the Pacific.
The Central Coast saw that with last weekend’s storm, which began as a tropical depression south of Cabo San Lucas on July 11. Fueled by ocean temperatures of 80-plus degrees, it rapidly intensified to a Category 4 hurricane as it traveled northwestward toward California.
Off the Baja California Peninsula, the hurricane hit a region of cooler seawater and gradually weakened — but not before reaching far enough northward to push copious amounts of rain over the Central Coast.
This monsoon moisture made for a very muggy night last Saturday, as towering cumulonimbus clouds moved northward toward San Luis Obispo. The air turned electric as flashes of lightning and rumbling thunder suddenly intensified by early Sunday morning, jolting awake most of the county. Unlike previous Central Coast lightning storms — such as those in August 2007 and September 2011 that produced electrical discharges for six to 12 hours — this system carried on for nearly 24 hours.
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While the other two squalls produced less than a third of an inch of rain, last Sunday’s system smashed rainfall records for July. Paso Robles received nearly 3.6 inches of the wet stuff. In fact, if you added up all the previous rain episodes in Paso Robles during July since 1948, the combined total would only reach about 1.5 inches. Adelaida got over 2 inches.
The previous record at Cal Poly was about a half- inch recorded on July 10, 1950. Last Sunday’s system bequeathed around 1.3 inches. Los Osos reported 2 inches.
According to the lightning tracker at SLOweather.com, thousands of lightning strikes were reported that Sunday. By early Sunday morning, strikes reached about 100 per minute.
Which leads to the question: What causes lightning? As relatively warm and moist air rises into the sky, it condenses and forms cumulus clouds that can tower over the earth. This condensation releases latent heat and, like turning on the burner in a hot-air balloon, it warms the surrounding air, which continues to rise at surprisingly high speeds. At times, it can reach more than 40,000 feet in altitude and actually break into the stratosphere.
The updrafts and downdrafts can create friction between rapidly moving ice particles and rain traveling in opposite directions. This wipes off electrical charges, increasing electrical pressure or voltage. The same effect can sometimes be experienced by rubbing your shoes across a wool carpet on a dry day and then touching a door knob. The shock you feel is the electricity discharged to the doorknob.
When electrical pressure or voltage becomes high enough, charges between parts of the cloud or between the cloud and the ground are released as lightning.
The majority of lightning strikes never hit the ground. When lightning does hit the ground, it starts with a relatively thin “leader” stroke from the cloud, followed immediately by a heavy return stroke from the ground.
Lightning discharges are incredibly powerful — up to 30 million volts at 100,000 amps. Just one bolt is more than six times hotter than the surface of the sun. The sudden increase in heat causes the air around the lightning bolt to rapidly expand, then collapse, causing the shock waves that we call thunder.
Lightning takes the path of least resistance and tends to hit the highest places. For that reason, never stand under a lone tree in an open field or on top of a mountain during thunderstorms. If you’re backpacking in the mountains and you feel your hair standing on end, get as low to the ground as you can and try to take cover.
Unfortunately, there really is no safe spot outside. As the National Weather Service will tell you, “When lightning roars, go indoors.”
On buildings, lightning rods allow electrons to stream off into the air or harmlessly to the ground. Wood structures and trees have high electrical resistance and can be heavily damaged unless grounded.
Did you know that PG&E delivers to its customers some of the nation’s cleanest electricity? More than 50 percent of the power comes from sources that emit no greenhouse gases, including Diablo Canyon nuclear power plant.