Weather Watch

Snow has fallen but not stayed

With Christmas just around the corner, people in our region often ask if it has ever snowed in San Luis Obispo.

Well the answer seems to be yes and no. Data from Cal Poly, which houses weather and climate records for San Luis Obispo, indicate no measurable snowfall has ever been recorded in town. Snowfall is measurable when there is at least one-tenth of an inch on the ground.

San Luis Obispo — with its low elevation and mild temperatures because of the strong marine influence from the Pacific Ocean — just doesn’t make a likely candidate for measurable snow.

However, over the years there have been reports of snow flurries in town along with some bone-chilling temperatures, but nothing that could be considered measurable snow.

For example, on Dec. 15, 1988, an intense storm from the eastern part of the Gulf of Alaska produced record amounts of snow in the North County (5 to 8 inches) and Santa Margarita (7 inches).

That day, San Luis Obispo reported 1.25 inches of rain, sleet and snow flurries with a low temperature of 35 degrees.

A few years later during December 1990, a strong southerly flowing jet stream from Alaska stretching southward to California moved a very cold Arctic air mass from the western Canada “Yukon express” down the West Coast.

There were reports of snowflakes in San Luis Obispo, and even Pismo Beach and Nipomo, on the night of Dec. 20, 1990, with overnight lows falling to the low 20s on the north side of the Cuesta Grade.

The next day, the meteorological tower at Diablo Canyon nuclear power plant reported sustained winds of 35 mph out of the north with gusts reaching 45 mph.

The temperatures dropped to the mid-30s right along the coastline. By Dec. 22, the winds at Diablo Canyon shifted out of the north-northeast with the temperature hitting the freezing point for the first time since Diablo Canyon started recording temperatures in 1976.

Gary Ryan, who was a meteorologist with the National Weather Service in Santa Maria, confirmed record-breaking low temperatures Dec. 22 and Dec. 23, 1990 throughout San Luis Obispo County.

Atascadero reached a bone-chilling 4 degrees while Templeton reached a numbing 9 degrees. San Luis Obispo reached 17 degrees. Even the coastline was cold, with Morro Bay reaching 25 degrees and Pismo Beach coming in at 29 degrees.

While the snowfall wreaked havoc on the community, the low temperature kept plumbers busy for days afterward repairing burst pipes and fixtures. In fact, many local hardware stores sold out of plastic and copper pipe and anything else to do with plumbing.

An Arctic air mass with very little moisture had moved over the Central Coast from Canada on Jan. 13, 2007.

The cold and dry airmass produced minimum temperatures in the mid-20s into the 30s along our coastline and in the teens in the North County. A few days later, an upper-level low passed over our area and produced rain and snow flurries at Diablo Canyon.

North of the Cuesta Grade, low-level cold air trapped in the valleys caused the rain to freeze on contact, a category of precipitation know as freezing rain.

While no official snowfall has been recorded in San Luis Obispo, that doesn’t necessarily mean it did not happen. Anyone with memories of a snowfall should drop me a line.

I received this e-mail from a reader named Ted about the December 1988 snow event: “It snowed on this morning — from Big Sur to Malibu — my son was born in Sierra Vista at 10:03 a.m. and I remember as labor was ending, the doctor commented on the rain and then snow!! and then Jesse was born !”

With that wonderful story, I wish everybody happy holidays!

This week’s forecast

A stationary 1,026 millibar eastern Pacific high centered 200 miles to the southwest of San Luis Obispo will give rise to gusty northeasterly (offshore) winds this morning.

These gentle to moderate (8 and 18 mph) northeasterly winds will come with higher gusts, especially in the eastern regions of San Luis Obispo, Cal Poly and the coastal canyons and passes. This offshore flow will produce clear, dry and warm temperatures.

Today’s high temperatures will reach the high 70s and maybe even the low 80s in the coastal valleys and along the beaches.

The record high in San Luis Obispo for Dec. 12 is 83 degrees, set in 1958. Cooler temperatures along with areas of morning fog will develop in the North County.

The winds will shift out of northwest later Monday. This condition will produce cooler temperatures Monday and especially Tuesday and Wednesday as night and morning fog and low clouds return along the coastline.

The longer-range surface and upper-level charts are indicating a major change in the weather pattern later this week.

A 1,010 millibar low pressure system is forecast to develop about 900 miles to the west of the Central Coast on Wednesday and intensify as it’s carried toward our coastline by an 100 mph westerly jet stream in the upper levels of the atmosphere.

Increasing southerly winds and the potential for moderate to heavy rain is forecast Thursday.

Surf and sea report

Today’s 3- to 4-foot northwesterly (295-degree deep-water) swell (with an 8- to 12-second period) will continue at this height and period through Monday morning.

Moderate to fresh (13 and 24 mph) with higher gust northwesterly winds will generate 4- to 6-foot northwesterly (300-degree deep-water) sea and swell (with a 4- to 11-second period) Monday afternoon through Tuesday.

A 988 millibar Gulf of Alaska storm will generate a 6- to 8-foot northwesterly (300-degree deep-water) swell (with a 12- to 14-second period) Wednesday.

Increasing southerly winds will produce a 7- to 9-foot south-southwesterly (200-degree deep-water) sea and swell (with a 5- to 9-second period) Thursday and will continue at this height and period through Saturday.

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

Conservation tip

You’re invited to the Diablo Canyon Power Plant Open House on Thursday, from 4 to 7 p.m. at the PG&E Energy Education Center. Light refreshments will be served.

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

For more information, please visit: www.diablocanyonpge.com

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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