Weather Watch

November proves unpredictable

The weather in November can be tough to predict. It can be cold and stormy, but big swells often make it a surfer’s favorite time of the year. Offshore winds tend to dominate the weather patterns in November. Last month proved that statement true.

During the first part of the month, we saw high pressure build over the Great Basin. The pressure produced gusty, warm and dry northeasterly (offshore) winds. In other words, the winds flowed from the land out to the Pacific Ocean.

On one morning in November, the Diablo Canyon meteorological tower reported offshore winds reaching 29 mph with gusts to 47 mph during early morning hours. This kept temperatures warm, and later that day San Luis Obispo hit a high of 91 degrees at Cal Poly.

In addition to the sunny skies, a very long-period swell arrived along the Central Coast. This swell was generated earlier by a monster 940-millibar storm located in the Gulf of Alaska with hurricane force winds.

The waves reached 23 feet with 20 seconds between the wave peaks at both the Cape San Martin and Harvest buoys. These powerful waves produced a thick, salty haze along the shoreline as they crashed on the beaches.

Temperatures at the beaches reached the mid-80s. Combined with the salty haze, it almost felt like the Central Coast transformed into the barrier islands off the North Carolina coast during a low tide at summer.

After a sunny start, the month of November changed gears, and a series of cold fronts combined with a polar jet stream allowed modified Arctic air to filter into the Central Coast, cooling us off dramatically.

The North County experienced bone-chilling temperatures in the low 20s. Even the coastal valleys were cold with widespread frost reported.

“The wind machines were all running overtime during the morning hours to keep sensitive avocado trees above freezing,” said Bill Coy, who grows avocados near Cayucos.

Generally the average monthly temperatures were below normal throughout the Central Coast. Paso Robles usually averages 52.7 degrees; this November it was 49.6 degrees. Cal Poly, home of record for climatology for San Luis Obispo, normally averages 58.2 degrees; last month it was 55.2 degrees.

November also brought below-normal rainfall. During November, 1.85 inches of rain were recorded at Cal Poly or 75 percent of normal. On average, 2.47 inches of rain falls during the month.

Paso Robles normally receives 1.26 inches; this November it was 0.9 inches or 71 percent of normal.

The rainfall totals reflect the ongoing condition of La Niña (colder than normal ocean water in the equatorial and eastern Pacific).

The National Oceanic and Atmospheric Administration’s Climate Prediction Center in Camp Springs, Md., still indicates that the current La Niña will peak this spring.

That will bring cooler surface seawater temperatures in the central and eastern equatorial Pacific. So far this year, seawater temperatures at Diablo Canyon have averaged a few degrees below normal.

Jan Null, a former National Weather Service lead forecaster and PG&E meteorologist, is recognized as an expert on El Niños and La Niñas and their relationship to California’s weather.

According to Null’s studies (see his web page at http://ggweather.com/enso.htm), La Niña periods usually produce below-normal rainfall, on average about 87 percent of normal on the Central Coast and even less in Southern California as the storm track is shifted northward.

One final note: A few meteorological models are predicting the return of El Niño late next year. If this condition develops, it could mean above-normal rainfall for the 2012 rain season (July 1, 2011 through June 30, 2012). This week’s forecast

Yesterday saw cloudy skies and widely scattered showers with most rain gauges in San Luis Obispo County reporting several hundredths of an inch.

Increasing southerly winds and extensive cloud cover will produce mild temperatures this morning.

A 1,001 millibar surface low-pressure system about 200 miles west of San Luis Obispo will move toward the Central Coast today with widely scattered sprinkles or rain showers. Southerly winds will increase later today, especially along the coast and in northwest-southeast oriented coastal valleys.

The 500-millibar analysis charts are indicating good upper-level enhancement of the associated front, which should pass the Central Coast between 5 and 10 p.m. with strong to gale force (25 and 38 mph) southeasterly winds, with gusts to 45 mph, and moderate to heavy rain.

These southerly winds will produce decent orographic enhancement — an air mass forced from a low elevation to a higher elevation as it moves over rising terrain — especially along the southwesterly-facing mountain slopes.

Rainfall amounts should range between one half and 1 inch in the coastal valleys. The coastal mountains may see up to 2 inches of rain by Monday morning. Snow levels will remain high at 6,000 to 7,000 feet Sunday evening, dropping to only 5,000 feet late Monday evening.

This system will quickly move out of the area by Monday morning, leaving behind partly cloudy to clear skies, mild temperatures and areas of dense night and morning fog.

A series of vigorous weather systems will move through the Pacific Northwest this week. However, the Eastern Pacific High will take a position off our coastline and will keep the storm track north of our area, keeping most of the rain north of Monterey Bay.

However, a few showers may develop over our area Wednesday morning.

Increasing northwesterly winds are forecast on Thursday and Friday, followed by gusty northeasterly (offshore) winds next weekend.

These offshore winds will produce dry and warmer weather with sparkling clear visibilities.

Surf and sea report

Increasing southerly winds will give rise to increasing southerly seas. These southerly (190-degree shallow-water) seas will build to 5 to 7 feet (with a 4- to 6-second period) by this afternoon and will continue at this height and period through tonight.

A 5- to 7-foot southwesterly (240-degree deep-water) sea and swell (with a 7- to 11-second period) is forecast along our coastline Monday, decreasing to 4 to 5 feet Tuesday.

A 965-millibar Gulf of Alaska storm is expected to produce a 1,200 mile-long northwesterly wind fetch (distance of water over which the wind blows) later Monday.

An 8- to 10-foot northwesterly (300-degree deep-water) swell (with an 11- to 16-second period) is forecast to arrive on our coastline from this system Wednesday, increasing to 9 to 11 feet (with a 14- to 16-second period) Thursday. This swell will decrease Friday.

Seawater temperatures will range between 54 and 56 degrees through tonight, increasing to 55 to 57 degrees Monday and will continue at this range through Wednesday.

Conservation tip

The public is invited to see the refurbished PG&E Energy Education Center and learn about Diablo Canyon on Thursday, Dec. 16 from 4 p.m. to 7 p.m.

The center is at 6588 Ontario Road, which is south of San Luis Obispo and is in between the two Avila Beach exits on Highway 101.

John Lindsey is a media relations representative for PG&E. He is also 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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