SLO County has had more rain than normal this season — and more may be on way
The October thunderstorms, followed by a cut-off low-pressure system that produced rain from Nov. 13 through 20, and additional heavy late-December rainfall, have resulted in well-above-normal precipitation totals across the Central Coast for this time of year.
The highest percentages of above-normal rainfall occurred in the southern and eastern portions of San Luis Obispo and Santa Barbara counties.
As of Christmas Day, Santa Barbara has recorded 16.54 inches of rain, about 330% of normal. By the way, the Santa Barbara Airport receives an average of 17.25 inches of rainfall for the entire rainfall season (July 1 through June 30).
Santa Maria Airport has reached 229% of normal, reporting 8.76 inches. Paso Robles has measured 7.55 inches, or 212% of normal.
Along the coast, San Luis Obispo Airport has so far received 8.13 inches of rain, equating to 141% of normal. Rocky Butte, typically the wettest location along the Central Coast, has reported 16.23 inches of precipitation, about 113% of normal.
Persistent Santa Lucia (northeasterly) winds during the first half of the month, combined with atmospheric river (Pineapple Express) conditions that transported warmer air from the south, produced one of the warmest Decembers on record. The average temperature in San Luis Obispo reached 58.9 degrees, 6.3 degrees above normal.
Paso Robles averaged 4.2 degrees above typical, while Santa Maria finished 4.9 degrees above average.
In contrast, Hanford in the San Joaquin Valley reported near-normal December temperatures, primarily due to persistent Tule fog during much of the month.
Looking forward, moderate to fresh (13 to 24 mph) northwesterly winds and partly cloudy skies, along with areas of fog, will develop on Saturday.
A strong Eastern Pacific High (1,033 millibars) off the Pacific Northwest will keep the storm track far north of the Central Coast. At the same time, high pressure over the Great Basin will produce fresh to strong (19 to 31 mph) Santa Lucia (northeasterly) winds at times gusty during the night and morning, decreasing during the afternoon on Sunday through Wednesday.
This condition will produce mostly clear skies, except for areas of dense ground fog in the coastal and inland valleys overnight. Also, Tule fog may redevelop in the San Joaquin Valley.
High temperatures over this period will reach the mid to high 60s throughout the Central Coast, with overnight lows dropping to the low to mid-30s in the inland valleys (Paso Robles) and low to mid-40s in the coastal valleys (San Luis Obispo) and along the beaches. Heavy Frost will likely develop in the inland valleys.
An upper-level low-pressure system is forecast to move northward from Baja California with a chance of rain showers on New Year’s Day. Rainfall is projected to be between 0.10 and 0.33 inches, if any occurs.
Dry weather will follow on Friday into next weekend.
Another chance of rain is expected on Jan. 5 and 6.
Surf report
A 6- to 8-foot northwesterly (295-degree deep-water) swell (with an 8- to 13-second period) is forecast along our coastline on Saturday, decreasing to 3- to 5-feet on Sunday.
A 2- to 4-foot northwesterly (290-degree deep-water) swell (with an 8- to 14-second period) is forecast on Monday and will remain at this level through Friday.
Seawater temperatures will range between 59 and 61 degrees through Friday.
On this date in weather history
2011: In summer, the Central Coast often has a sharp temperature difference between the cool, foggy beaches and the hot, dry inland valleys. This December morning was the opposite. At 8 a.m. both Diablo Canyon and the Point San Luis Lighthouse reported morning lows of 60-degrees. At the same time, the Santa Margarita Fire Department reported it was 25 degrees. That’s a 35-degree temperature gradient between the beaches and the inland areas.
2020: A vigorous 539 dm upper-level low-pressure system produced gusty southwesterly winds and moderate to heavy rain. The Diablo Canyon Rain Gauge measured 1.80 inches of rain which was the highest 24-hour reading since Jan. 9, 2017, when 2.09 inches of rain fell.
This week’s temperatures
LOWS AND HIGHS, PASO ROBLES
SUNDAY: 35, 55
MONDAY: 34, 59
TUESDAY: 33, 64
WEDNESDAY: 36, 62
THURSDAY: 39, 60
FRIDAY: 37, 58
SATURDAY: 37, 61
SUNDAY: 39, 65
LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS
SUNDAY: 43, 62
MONDAY: 42, 66
TUESDAY: 44, 68
WEDNESDAY: 44, 68
THURSDAY: 44, 68
FRIDAY: 44, 68
SATURDAY: 44, 68
SUNDAY: 44, 68
John Lindsey is a retired PG&E marine meteorologist. Email him at JohnLindseyLosOsos@gmail.com or follow him on X @PGE_John.