Weather Watch

Oh, what a lovely dry month

It’s been dry, really dry. San Luis Obispo has only recorded 0.18 inches of rain since Nov. 21. According to rain records from Cal Poly, the official home of climatology for San Luis Obispo, December through January is approaching the driest ever. The records go back to the 1860s.

The driest December-through-January period occurred during the 1976 rain season, which recorded only 0.19 inches of precipitation at Cal Poly.

Hopefully, the expected rain later this month will keep the 1976 record intact.

We’ve also seen the least amount of prefrontal southerly winds on record during the December-January period according to wind records that reach back to 1976 at the Diablo Canyon Meteorological Tower.

This year has also seen endless cycles of night and morning northeasterly (offshore) winds. This offshore flow has produced a lot of cold mornings and mild and sunny afternoons. I can’t recall a January that’s produced more spectacular sunsets due to the mostly clear to partly cloudy skies.

This year’s La Niña cycle is probably the cause. La Niña cycles produce stronger-than-normal trade winds across the equatorial Pacific. This condition triggers a greater amount of upwelling along the North and South American Pacific coastlines, which gives rise to cooler surface seawater temperatures.

These cooler waters tend to keep a persistent ridge of high pressure over California that often forces the storm track toward the Pacific Northwest, leaving the Central Coast with less rain. While extensive upwelling is certainly good for fish that depend on the oceanic food web, agriculture, industry and households may need to conserve water to a greater extent.

So far this year, the La Niña cycle has kept the jet stream far to the north. In fact, so far north that it has brought record-breaking snows to many parts of Alaska. From July 1 through Friday, Anchorage received about 82 inches of snow, making it the snowiest period for Anchorage since records have been kept. East of Anchorage, Valdez has seen an amazing 318 inches or 26.5 feet of snow this season!

Farther south it’s a different story.

Historically, December and January produce a large fraction of total precipitation during the rain season. Recovery from this rain deficit will be difficult but not impossible.

Back in 1990, the rain season was the driest on record, with only about 8 inches recorded in San Luis Obispo. Hope for a wetter 1991 season faded as San Luis Obispo County moved into February with the driest rain season in its history.

After five years of below-normal rainfall throughout our state, California’s lakes and massive reservoirs were nearly empty. Both Santa Margarita and Nacimiento lakes were at 6 percent of capacity; Lopez Lake had fallen to 39 percent of capacity.

Communities throughout San Luis Obispo County and the state instituted water rationing and many coastal communities contemplated seawater desalination.

I remember the coastal mountains turned from the normal golden browns and red hues of summer to more of an ash gray color. Many of our streams and creeks stopped flowing and the local ranchers and farmers were at their wits’ end.

In January 1991, the seawater temperatures in the equatorial and eastern Pacific Ocean warmed, reaching a strong El Niño classification later in the year. The pressure block over the Hudson Bay in northeastern Canada dissolved and the high pressure ridge over California shifted, allowing the storm track to move over our state.

The skies opened in March and a pair of storms dropped more than 4 inches of rain in San Luis Obispo during the first week of March, more rain than almost anyone could have hoped for. The miracle rains of March continued as a series of storms swooped down from Alaska.

A vigorous and very cold low-pressure system produced up to 10 inches of snow on the Cuesta Grade and 2 to 4 inches of rain in the coastal valleys during the middle of the month. Parts of the North County turned into a “winter wonderland.”

Overall, nearly 13 inches of rain fell that March.

The Climate Prediction Center in Camp Springs, Md., is still advertising that the current La Niña will continue through the rest of winter and should continue to produce below-normal rainfall. We have never had above-normal precipitation in back-to-back years with a La Niña cycle.

Today’s forecast

An upper-level low pressure system will move over Santa Barbara County this morning with extensive clouds and sprinkles and maybe even a few light rain showers.

Today’s high temperatures will only reach the mid- to high 50s throughout San Luis Obispo County.

A cold front will follow producing strong to gale force (25- to 38-mph) north to northeasterly (offshore) winds tonight into Martin Luther King Jr Day.

A pattern of moderate to fresh (13- to 24-mph) northeasterly (offshore) winds developing during the night and morning hours, shifting out of the northwest during the afternoon hours, will begin Tuesday and will continue through Thursday. This cycle will give cold and clear mornings and mild and sunny afternoons.

The increasing midlatitude westerly winds across the Pacific Ocean will signal a major change in the weather pattern.

A significant weather event with potential moderate rain and strong southerly winds, especially across the coast range and Sierra with snow levels initially above 7,500 feet, is forecast to develop along the central coast Friday into next weekend. The models are indicating that the storm track will shift further southward the following week. This should give the potential for even for greater amounts of rainfall at the end of January.

Today’s surf report

Today’s 3- to 4-foot west-northwesterly (290-degree deep-water) swell (with an 11- to 13-second period) will remain at this height through this afternoon.

Strong to gale force (25- to 38-mph) northerly winds along the coastline will generate an 8- to 10-foot northwesterly (320-degree deep-water) sea and swell (with a 5- to 12-second period) tonight into Monday.

A 5- to 7-foot northwesterly (300-degree deep-water) swell (with an 11- to 13-second period) is forecast along our coastline Tuesday, decreasing to 3 to 5 feet with the same period Wednesday into Thursday.

Preliminary extended surf analysis:

This morning’s surface charts and models are indicating a series of intense midlatitude storms along with associated gale force westerly winds this week. If this condition develops as advertised, a series of high-energy west-northwesterly swell events may arrive along the Pecho coastline beginning Friday and continuing through Jan. 24.

The first in the series of these wave events is expected to peak Saturday at 14 to 16 feet (with a 15- to 17-second period). Wave heights at the offshore buoys may exceed 23 feet.

Seawater temperatures

Seawater temperatures will range between 53 and 55 degrees through this week.

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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 nearly 26 years. To subscribe to his daily weather forecast or ask him a question, email pgeweather@pge.com.

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