Weather Watch

Illuminating the mystery of St. Elmo’s Fire

While stationed aboard the USS Trippe in the Caribbean Sea in 1983, our ship’s weather radar showed an intense band of thunderstorms bearing down on our location. I recall thinking at the time that this would be a terrific opportunity to take some great time-lapse photographs, so I headed to the weather deck on top of the ship’s bridge.

Suddenly, I noticed the tip of the ship’s mast had a haunting bluish-white halo, with brush-like sparks of electricity discharging into the night sky. A salty old chief on board the ship referred to it as St. Elmo’s Fire.

The scientific name for this phenomenon is a corona discharge, and it often occurs before a lightning storm strikes.

In addition to masts of ships, St. Elmo’s Fire can also be observed on the wingtips, antennae, Pitot tubes and edges of propellers on aircraft in the vicinity of thunderstorms.

This atmospheric marvel is caused by severe turbulence, specifically updrafts and downdrafts found in thunderstorms, which can produce friction between rapidly moving ice particles and rain traveling in opposite directions. This wipes off electrical charges, which produce an increase in voltage.

Nature abhors an imbalance, so when electrical voltage becomes high enough on pointed objects in the atmosphere, a current of electrons will begin to flow outward. If enough current flows, the molecules of air near the object will ionize and explode with luminosity, creating St. Elmo’s Fire.

To use the garden water hose analogy, voltage is equivalent to the water pressure in the hose. If the pressure in the water hose becomes too great, small water leaks develop, allowing water to jet out in narrow streams.

Historically, sailors felt that St. Elmo’s Fire was a favorable omen and were thankful for its presence. However, if you see St. Elmo’s Fire you should take cover as lightning may strike.

A special thanks

With Thanksgiving Day approaching rapidly, here is a story I would like to share.

At last Wednesday night’s turkey drive for the Food Bank Coalition of San Luis Obispo County in front of Sierra Vista Medical Center in San Luis Obispo, Koby Wescom of Paso Robles stopped by with his parents and friends. About a week before, Koby’s parents asked him what he wanted for his ninth birthday and he said, “To make sure that every family had enough food to put on the table.”

He and 15 of his friends then proceeded to collect more than 450 pounds of food and donated it to the food bank that night.

Because of the actions of Kobe and his friends and family, many families will be able to celebrate the Thanksgiving season.

This week’s forecast

A cold front passed Diablo Canyon early Saturday at 4 a.m. and produced moderate rain followed by gusty northwesterly winds.

A 999-milibar low-pressure system will move south over our area this morning. This weather system is cold and convective in nature and will bring periods of moderate rain showers, strong to gale force (25 and 38 mph) southwesterly winds, and the chance of hail and thunder. Temperatures will only reach the mid-50s today.

Heavy snow will fall across the Sierra with as much as a foot of snow above 2,500 feet.

Rain showers and cloud cover will decrease later this morning with periods of sunshine developing by this afternoon.

However, scattered rain showers, especially over the mountains, could still develop during the afternoon and evening hours.

Expected precipitation totals should range between 0.33 and 0.75 inches with higher amounts in the coastal mountains by this afternoon.

Partly cloudy and cool weather is forecast tonight through Monday with only a slight chance for rain showers. Overnight lows will reach the mid-30s and afternoon highs will only be in the 50s throughout San Luis Obispo County.

Another cold band of light rain showers may cross the Central Coast from north to south early Tuesday morning. If it does rain, precipitation totals will be light. However, the system will produce additional snow in the Sierra down to 2,000 feet.

The Eastern Pacific high will develop off our coastline late Tuesday and a surface high will build over the Great Basin.

This condition will produce night and morning northeasterly (offshore) winds. This offshore flow will give dry, clear and warmer weather with plenty of sunshine Thanksgiving Day through Saturday.

Another cold front may produce rain showers next Sunday.

Surf and sea report

A 10- to 12-foot northwesterly (300-degree deep-water) sea and swell (with a 5- to 12-second period) is forecast to arrive along our coastline late this morning and will remain at this height and period through this afternoon.

Note: Wave heights will be higher at the offshore buoys.

Combined with this northwesterly sea and swell will be 5- to 7-foot southwesterly (225-degree shallow-water) seas this morning.

This northwesterly (300-degree deep-water) sea and swell will decrease to 8 to 10 feet by Monday morning, further lowering to 5 to 7 feet (with a 7- to 11-second period) by Monday night.

A 4- to 6-foot northwesterly (300-degree deep-water) swell (with an 8- to 17-second period) will arrive along our coastline on Tuesday, increasing to 5 to 7 feet Wednesday.

This northwesterly swell will rapidly decrease on Thursday to 3 to 5 feet, further lower to 1 to 2 feet (with an 8- to 10-second period) Friday and should remain at this height and period through Saturday.

Increasing swell from the northwest will arrive along the Central Coast Nov. 29, further building Nov. 30.

Conservation tip

Replace traditional incandescent holiday lights with Energy Star light emitting diode — LED — lights. For information, visit www.pge.com/my home.

John Lindsey is a media relations representative for PG&E. He’s a local weather expert and has lived along the Central Coast for more than 23 years. To subscribe to his daily weather forecast or ask him a question, e-mail pgeweather@pge.com.

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