San Luis Obispo County’s topography plays an important role in our weather. The Santa Lucia mountain range helps to shelter many parts of the North County from the marine influence of the Pacific Ocean.
This condition regularly produces much greater temperature extremes in the summer and winter months than south of the Cuesta Grade.
As the northwesterly (onshore) winds blow horizontally across the Pacific toward the Central Coast, the air mass is lifted over the Santa Lucias, where it cools and eventually reaches its dew point temperature.
When this occurs, fog will develop on the windward side of the mountain, almost like a hand of white mist covering the top of the ridge.
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As the air mass descends down the other side of the mountain range, it warms and the fog disappears.
Nevertheless, when the atmospheric conditions are right, marine air can make its way from Monterey Bay, surging southward through the Salinas Valley toward San Miguel.
For those living south of Paso Robles, the Templeton Gap provides an excellent pathway for the marine air. The Templeton Gap is a series of passes through the Santa Lucia Mountain Range that are more or less near Highway 46 from Cambria. It allows marine air to flow toward Templeton and Atascadero.
The average maximum temperature at the Paso Robles Airport during July is 93.8 degrees, while the average maximum temperature in Atascadero in July is a much cooler 85.7 degrees, according to the Air Pollution Control District’s monitoring station there. These cooler summer temperatures in Atascadero are caused in large part by the Templeton Gap.
More interesting, there is less air pollution near the Templeton Gap. Ozone or smog is formed when the sun’s rays produce a photochemical reaction with oxides of nitrogen and reactive hydrocarbons, mostly from the exhaust of cars and trucks that are powered by fossil fuels.
Usually the peak ozone in the north county occurs during late summer afternoons when the sun is directly overhead and its radiation is most intense.
But often ozone levels drop dramatically in the middle of the day in Atascadero when the sea breeze makes its way through the Templeton Gap, bringing with it the clean ocean air.
This week’s forecast
The soundings from Vandenberg Air Force Base indicate a temperature inversion layer at more than 2,000 feet. This condition will allow the marine layer to move far inland this morning.
It will burn off from the interior and most of the coastal valleys by this afternoon, but will be stubbornly persistent along the coastline, especially the northwesterly facing beaches which may not see the sun at all today.
Today’s temperatures will range from the mid- to high 70s in the North County and the high 60s to low 70s in the coastal valleys. Temperatures along the coastline will mostly range from the high 50s to the low 60s along the northwesterly facing (Los Osos) beaches and low to high 60s along southerly (Avila Beach and Cayucos) beaches today.
The rainy season just seems to want to hold on a little longer.
The upper-level charts are indicating the storm track will shift southward toward our area tonight, producing a major change in weather.
A late-season 1,005-millibar low pressure system will move eastward over Monterey Bay on Monday. The associated cold front will pass our area Monday afternoon with moderate to fresh (13 and 24 mph) southeasterly winds, increasing clouds and rain. Rainfall amounts will range between 0.05 and 0.25 inches from Monday afternoon through Monday night.
Temperatures will cool significantly Monday, with maximum readings only reaching the low 60s.
Overall, the next week looks cool and dry after Monday. Temperatures will warm Tuesday through Wednesday with the interior reaching the low to mid-80s by Thursday.
Temperatures in the coastal valleys will mostly be in the mid-70s.
A different story will play out along the coastline as we move back into a spring type of weather pattern. Strong to gale force (25 and 38 mph) northwesterly (onshore) winds late Wednesday into Friday will produce a cooling trend along our beaches.
Surf and sea report
Today’s oceanographic conditions favors the surfers and those fishing but may not shine brightly on the scuba divers as the seawater visibility has become murky as a long period southern hemisphere swell arrives along our coastline.
Today’s 3- to 4-foot southern hemisphere (200-degree deep-water) swell (with 15- to 17-second period) will remain at this height and period through tonight, gradually decreasing Monday.
Combined with this southern hemisphere swell Monday afternoon and night will be 2- to 4-foot short-period (190-degree shallow-water) seas.
Increasing northwesterly winds along the entire California coastline will produce 3- to 5-foot (300-degree deep-water) sea and swell Tuesday afternoon through Wednesday morning, building to 5 to 7 feet Wednesday afternoon and night.
This northwesterly sea and swell will further increase to 6 to 8 feet (with a 5- to 14-second period) Thursday through Friday.
A 3- to 5-foot southern hemisphere (225-degree deep-water) swell (with an 18- to 20-second period) is expected to arrive along our coastline Saturday, increasing to 4 to 6 feet (with a 16- to 18-second period) next Sunday.
Another significant southern swell may arrive along our coastline May 29.
Seawater temperatures will range between 51 and 54 degrees through Tuesday, decreasing to 51 to 53 degrees Wednesday.
The seawater temperatures will further lower to 49 and 51 degrees Thursday through Friday.
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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. If you have a question, send him an e-mail at email@example.com.