October’s weather can get real screwy

This year it lived up to its reputation as a fire and ice month

San Luis Obispo - The TribuneNovember 3, 2012 

Looking back at this October, we found a mixed bag of weather conditions. San Luis Obispo County can experience wide fluctuations in temperatures at this time of the year.

October can easily produce triple-digit temperatures in the coastal valleys and even along the beaches. Nevertheless, it can also give the first frost of the season in the North County. Windrose Farm near Creston reported a morning low temperature of
30.7 degrees Oct. 24.

October lived up to its reputation as a fire and ice month.

Chronologically, an area of high pressure often builds at the surface over the Great Basin, producing northeasterly (offshore) winds. These winds flow from land out over the Pacific Ocean and bring a relatively warm and dry air mass to our shoreline, pushing the marine layer far out to sea. The average October high temperature in San Luis Obispo is
75.3 degrees. This October, the average high temperature was 76.5 degrees, warmer than normal.

This October started out hot, as gusty northeasterly (offshore) winds produced clear skies and high temperatures across San Luis Obispo County. The first day of October saw high temperatures reach the low 100s in many parts of the county. On Oct. 2, Cal Poly, home for climatology for San Luis Obispo, hit 96, breaking the record of
94 degrees set in 1995.

In 1987, a scorching heat wave developed in California, and San Luis Obispo was the warmest location for the nation, with 111 degree temperatures recorded at the airport for two days in a row.

Because of the warm overnight temperatures, many Cal Poly students who lived in the red brick dorms on campus slept outside, including me. The air conditioners were not operating and the dorms quickly warmed up like an enormous brick oven.

On Oct. 11, a storm hit the Central Coast and was unlike any other weather system that I’ve seen. A large and slow-moving cutoff low in the upper levels of the atmosphere moved south along the California coast and progressed into Southern California. This high-level system brought a 10- to 30-mile-wide band of moderate rain that stretched from Creston southwestward over San Luis Obispo toward Los Osos and out over the Pacific Ocean. This high-
elevation band of moisture dropped a surprising amount of rain over a narrow area as it stalled. Cal

Poly recorded 1.05 inches of rain, ending a long dry spell. This narrow band of rain produced 1.12 inches of rain at Mickey’s rain gauge in south Atascadero, while just six miles away the Templeton rain gauge at the Sheriff’s Office station near the intersection of Highway 101 and Main Street only recorded 0.04 inches of rain.

Normally in the month of October, San Luis Obispo receives nearly 1 inch of rain on average. This system produced above-
normal October rainfall for San Luis Obispo. However, areas in northern and southern San Luis Obispo County were well below normal.

By the latter half of the month, a more familiar October weather pattern developed with night and morning northeasterly (offshore) winds followed by afternoon northwesterly (onshore) winds. On Oct. 26, the northeasterly (offshore) wind gust reached 50 mph at Diablo Canyon.
These offshore winds produced warm temperatures along the beaches with late morning and early afternoon highs reaching into the low to mid-80s.

These offshore winds were so strong they generated rare northeasterly seas. Normally, the average wave height at the Diablo Canyon Waverider buoy during October is 4.6 feet, but this October the average height was 4.4 feet because of the lack of any storms. The highest average was 5.8 feet set back in 1986.

Seawater temperatures along our coastline reached the low 60s. Seawater temperatures usually average 57.7 degrees during October at the Diablo Canyon Power Plant Ocean Lab.

Overall, October 2012 in California was generally warmer than normal. Of course, the major weather story of October was Hurricane Sandy that struck the Northeast. This storm may become one of costliest natural disasters on record. When you look at the list of the costliest storms adjusted for inflation over the past hundred plus years, 6 of the 10 storms occurred between 2000 and 2010, according to the National Hurricane Center in Miami. Last week, PG&E sent 250 electrical system personnel, including four PG&E employees from San Luis Obispo County, to help restore power in New York City.

Today’s forecast

A ridge of high pressure over California and the Great Basin will continue to produce a pattern of moderate to fresh (13- to 24-mph) northeasterly (offshore) winds during the night and morning hours.

These winds will produce sunny, clear and warm weather. Today and Monday’s high temperatures will range between the low and high 80s throughout San Luis Obispo County.

The predominant wind flow will turn onshore by Wednesday. This condition should allow the marine layer to redevelop along the coast, producing night and morning low clouds and fog and cooler temperatures.

A strong and cold upper-level low-pressure system is forecast to move through California on Thursday into Saturday. The system will produce increasing northwesterly winds, scattered rain showers and much cooler temperatures. In fact, high temperatures on Thursday and Friday will reach into the high 50s. In other words, it’s going to feel much like winter. Snow levels could drop to 3,000 feet Friday and Saturday.

Today’s surf report

An intense storm developed in the Gulf of Alaska on Friday. A 4- to 6-foot northwesterly (310-degree deep-water) swell (with a 15- to 17-second period) from this storm will arrive along the coast later this morning, increasing to 6 to 8 feet with the same period this afternoon into tonight.

This Gulf of Alaska northwesterly (295-degree deep-water) swell will gradually decrease to 5 to 7 feet (with a 13- to 15-second period) on Monday, further lowering to 4 to 6 feet Tuesday.

A 3- to 5-foot northwesterly (290-degree deep-
water) swell (with an 8- to 13-second period) will develop Wednesday.

Strong to gale force (25- to 38-mph) northwesterly winds will generate a 5- to 7-foot (320-degree deep-water) sea and swell (with a 7- to 11-second period) on Thursday.

The northwesterly winds will further increase to moderate gale to fresh gale (32- to 46-mph) levels

Friday through Saturday. These winds will generate a 7- to 9-foot northwesterly (320-degree deep-water) sea and swell (with a 7- to 11-second period) Friday through Saturday.

Seawater temperatures

Seawater temperatures will range between 55 and 57 degrees through Wednesday, decreasing Thursday through next Sunday.

John Lindsey’s column is special to The Tribune. He is a media relations representative for PG&E and a longtime local meteorologist. If you have a question, send him an email at pgeweather@pge.com.

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