Atmospheric river to bring another week of rain to SLO County. Here’s when and how much

Last week’s storms brought Paso Robles’ rainfall total to nearly 9 inches for this rain season (July 1 through June 30).

On average, by the end of January, the Paso Robles Airport has recorded about 7 inches of rain.

Cal Poly (home of climatology for San Luis Obispo) has reported around 11 inches of rainfall this season, or 1 inch below the expected average by the end of this month.

Meanwhile, the numerical models suggest a dynamic start to February. The initial 11 days of the month might witness substantial rainfall, ranging from 3 to 5 inches across most of the Central Coast, with higher amounts in the Santa Lucia mountains.

If the models verify, rainfall totals could reach well above normal levels throughout the Central Coast in a classic El Niño manner.

By the way, NOAA’s Climate Prediction Center is indicating the current strong El Niño condition will transition to a La Niña pattern, which typically produces below-average rainfall by next winter.

An upper-level ridge of high pressure over California will produce moderate to fresh (13 to 24 mph) Santa Lucia (northeasterly) winds during the overnight and morning and mainly clear to partly cloudy skies on Sunday through Tuesday.

Daytime temperatures will reach the mid-70s throughout the Central Coast, with overnight lows dropping to the mid-40s in the inland valleys (Paso Robles) and mid-50s in the coastal valleys (San Luis Obispo) and along the beaches.

This area of high pressure that produced Chamber of Commerce weather is forecast to weaken and move eastward on Wednesday, opening the door to a series of storms.

The first low-pressure system (973 millibars) will move toward the Pacific Northwest.

The associated cold front, strengthened by vigorous upper-level winds, will tap into a plume of subtropical moisture (atmospheric river) and move through the Central Coast Wednesday night into Thursday morning with strong to gale-force (25 to 38 mph with gusts to 45 mph) southerly winds and moderate to heavy rain.

This storm is expected to produce between 1 and 2 inches of rain, with higher amounts in the Santa Lucia mountains.

Strong to gale-force (25 to 38 mph) northwesterly winds, much cooler temperatures, partly to mostly cloudy skies, with scattered rain showers are forecast for Thursday afternoon into Friday.

Another storm is expected to arrive next Saturday and Sunday with gale-force winds and moderate to heavy rain.

This unsettled weather pattern, with storms passing on a three-day interval, will likely to continue through the following week.

Surf report

A 5- to 7-foot west-northwesterly (285-degree, deep-water) swell (with an 11- to 14-second period) is forecast along our coastline on Sunday through Wednesday afternoon.

Increasing southerly winds will generate a 6- to 8-foot southerly (190-degree, shallow-water) seas on Wednesday night into Thursday morning, followed by a 10- to 12-foot northwesterly (290-degree, deep-water) sea and swell (with a 5- to 14-second period) on Thursday afternoon into Friday.

Seawater temperatures will range between 58 and 60 degrees through Wednesday, decreasing to 54 to 56 degrees on Thursday into Saturday. .

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

John Lindsey is a retired PG&E marine meteorologist. Email him at JohnLindseyLosOsos@gmail.com or follow him on Twitter @PGE_John.