SLO County forecast calls for winter weather with crisp temperatures, clear skies
The Eastern Pacific High off the California coast may keep storm conditions away from Central California through at least the first half of December and possibly right up to Christmas.
Upper-level winds, which typically steer storms our way, are being pushed north into the Pacific Northwest, following a classic La Niña pattern.
This situation raises an interesting question: Has San Luis Obispo County ever experienced a completely dry December?
Yes, it has.
Both 1876 and 1989 recorded no measurable rainfall at Cal Poly, which has long served as a local climatology reference point.
Unsurprisingly, those rainfall seasons (from July 1 to June 30) finished well below average. The 1876 to 1877 season brought only 8.15 inches of rain, and the 1989 to 1990 season recorded 13.36 inches. Cal Poly typically receives about 23 inches of rain annually.
This week, San Luis Obispo County can expect dry weather with cool nights and mornings, followed by mild to warm afternoons. These conditions will persist through mid-December.
A strong 1,029-millibar Eastern Pacific High, located roughly 700 miles offshore, combined with a 1,025-millibar high over the Great Basin, will generate moderate to fresh (13 to 24 mph) and occasionally gusty Santa Lucia (northeasterly) winds during the night and morning. Winds will ease and shift out of the north-northwest each afternoon through next week.
This weather pattern will maintain clear skies, except for periods of high-level cirrus clouds and dry conditions.
However, prolonged dry spells in December often lead to the development of Tule fog in the San Joaquin Valley. Anyone living in or traveling through the Valley during winter knows how treacherous Tule fog can become, especially after rainfall.
Low temperatures will range from the low 40s in the inland valleys (such as Paso Robles) to the mid-to-upper 40s in the coastal valleys and beaches (like San Luis Obispo). Temperatures in the afternoon are likely to climb into the upper 60s to mid-70s throughout the area.
No significant rainfall is forecasted through the end of December.
Surf report
A 5- to 7-foot northwesterly (290-degree, deep water) swell (with an 8- to 15-second period) is forecast along our coastline through Wednesday, increasing to 6 to 8 feet (with a 7- to 17-second period) on Thursday into Friday.
This northwesterly swell will decrease to 3 to 5 feet (with an 8- to 12-second period) next Saturday and Sunday.
Seawater temperatures will range between 60 and 63 degrees through Friday.
On this date in weather history (Dec. 7)
1941: “A date which will live in infamy. The United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan,” Franklin D. Roosevelt said.
2010: An energetic front produced gusty southerly winds and periods of heavy rain. It’s worth noting that most areas of the county saw about 0.75 inches of rain on average. The southwesterly winds reached 36.7 mph sustained with gusts up to 55.5 mph at the Diablo Canyon meteorological tower.
2013: Low relative humidity levels, very cold air mass and clear skies combined to produce cold temperatures throughout San Luis Obispo County in the morning. The morning’s low temperatures reached 27 degrees in San Luis Obispo and 17 degrees in Paso Robles. Both Creston Elementary School and Windrose Farm hit a low of 11 degrees. Calvin reported a low of 9.7 degrees in Adelaida.
2020: A massive 941-millibar storm with hurricane-force winds developed in the Gulf of Alaska. The Ocean Station Papa CDIP Waverider Buoy in the Gulf of Alaska reached 41 feet.
This week’s temperatures
LOWS AND HIGHS, PASO ROBLES
SUNDAY: 40, 68
MONDAY: 41, 69
TUESDAY: 42, 72
WEDNESDAY: 44, 73
THURSDAY: 44, 74
FRIDAY: 44, 73
SATURDAY: 42, 70
SUNDAY: 43, 71
LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS
SUNDAY: 48, 73
MONDAY: 49, 73
TUESDAY: 49, 76
WEDNESDAY: 50, 76
THURSDAY: 50, 77
FRIDAY: 49, 75
SATURDAY: 48, 74
SUNDAY: 50, 75
John Lindsey is a retired PG&E marine meteorologist. Email him at JohnLindseyLosOsos@gmail.com or follow him on X @PGE_John.