Coldest December in SLO since ’71? Probably

This is proving to be the coldest December in San Luis Obispo County in 40 years, according to a new analysis of high and low temperatures by local weather expert John Lindsey.

The month is not over yet, he cautioned. Still, through Wednesday, this December is colder than any other final month of the year going back to 1971, which is the coldest December on record, Lindsey said.

His analysis of temperature readings taken at Cal Poly puts numbers to what many locals have been feeling: It really has been cold, especially overnight.

The average high temperature for the month based on record-keeping that started in 1948 is 64.5 degrees, Lindsey said. So far this month, the average high has been 61.5 degrees.

The average low this month has been 37.4 degrees. That’s well below the historical average of 42.1 degrees. If the highs and lows are put together and averaged, this month has had a temperature of 48.5 degrees, far off the historical average of 53.3.

Other highlights this December:

• The daytime high has not yet reached 70 degrees at Cal Poly. On Dec. 1 and again Dec. 17, the high was 68 degrees, the warmest so far. On Dec. 12, the high was only 52.

• Fourteen of 20 nights have had lows in the 30s. The coldest overnight reading occurred Dec. 4, when the thermometer dipped to 31.5 degrees.

Lindsey only analyzed temperatures taken at Cal Poly, because that is where official readings for San Luis Obispo are taken. Conditions in the North County and along the coast have been different. Lows in the North County, for example, have been in the 20s.

The reason for the cool conditions is also why it has been so dry: Pervasive high pressure is directing any chance of storms far to the north. In place of clouds and rain, the region has experienced cold nights and clear but cool days.

Today marks the first full day of winter and is also the day with the least amount of daylight. The winter solstice occurred at 9:30 p.m. Wednesday, the moment when the sun was at its lowest point in the Northern Hemisphere. From today on, the days will get progressively longer until daylight peaks on the summer solstice in June.

While ’tis the season of short days, the county can enjoy clear weather, at least south of the Cuesta Grade, through Christmas weekend. Thick valley fog will continue to sock in parts of the North County during early morning hours, said Lindsey, who has been forecasting Central Coast weather for more than two decades.

Lindsey, a community relations specialist with PG&E, said offshore winds could develop in the morning Friday and Christmas Eve and be strongest in coastal passes and along the eastern side of San Luis Obispo and near Morro Bay High School.

The National Weather Service is expecting offshore winds in areas of Ventura and Los Angeles counties as well. Daytime highs today and Friday will be in the low 60s countywide, then warm to the upper 60s in San Luis Obispo and Pismo Beach on Saturday and Christmas Day. Sunday will stay in the low 60s in the North County.

Overnight lows in Paso Robles will be in the upper 20s, while lows in San Luis Obispo will be in the 30s. Lindsey said the high pressure will weaken near the end of next week, but all the Central Coast can hope for are high clouds while storms blow through Northern California.

So far this month, it has rained only on Dec. 12, when 0.16 inches was measured at Cal Poly. The rainfall average for the month of December is 3.79 inches.