The month of April has certainly lived up to its reputation as a transition month between the cool and blustery weather of winter and the warm and dry weather of summer. Normally the rainfall in April quickly tapers off with San Luis Obispo averaging only about 1.7 inches of precipitation, but there have been exceptions.
According to general climate summaries for San Luis Obispo at Cal Poly — home of record for climatology for San Luis Obispo — the wettest April occurred in 1967 when 6.9 inches of rain was recorded. The second wettest April occurred in 2006, which recorded 5.28 inches of the wet stuff.
This April, the rain gauge at the Diablo Canyon Ocean Lab recorded only 0.17 inches of rain; last year during April it was 1.61 inches. Completely dry Aprils occurred in 1973 and 2004 with no measurable rain reported.
In addition, this April was cool. Whether you are a surfer, a scuba diver, fisherman or just a casual beach visitor, you have probably noticed cold seawater temperatures recently.
Since 1976, the Diablo Canyon nuclear power plant has monitored and recorded seawater temperatures along the Pecho Coast as part of the plant’s environmental monitoring program. Over the last week, relentless northwesterly winds have produced a great amount of upwelling.
The Patton Cove temperature-monitoring station, which is just south of the power plant, has an average yearly seawater temperature of 55.3 degrees Fahrenheit. This week, seawater temperatures have reached a bone-chilling 48.5 degrees near the power plant.
Not only has the Pacific been cold, but air temperatures — especially in the North County — were below average during the first part of the month.
Below-freezing temperatures at this time of the year can be a major problem for our grape growers.
It is interesting to note that on April 8, a very cold upper-level low pressure system moved over the Central Coast, producing well below seasonal temperatures. This system also produced areas of heavy hail and even snow in the higher elevations of San Luis Obispo County.
The next morning, a late-season freeze in the North County damaged the bud break on many vines just as the young green shoots were reaching for the sun.
Dave King of Vista Del Rey Vineyards, located six miles north of Paso Robles, near the eastern slope of the Santa Lucia Mountains, said below-freezing temperatures burned nearly one-third of his dry-farmed zinfandel vineyard.
“We will have to wait to see what the full extent of the damage will be,” he told me.
“This freeze extended from King City all the way south to Santa Margarita, just about everywhere north of the Cuesta Grade,” he went on to say.
Another vintner told me it was as though somebody with a blowtorch had walked up and down their vineyards.
The late-season freeze also hampered the flower bloom in the eastern part of San Luis Obispo County, especially around the Carrizo Plain National Monument.
However, despite the damage to the North County vineyards and wildflowers, it pales in comparison to what has occurred east of the Rocky Mountains.
Nearly 600 tornadoes have been reported in the United States this April, leading the National Weather Service to predict that the month could have the most confirmed tornadoes of any month on record.
However, multiple sightings of single tornadoes were reported, so we will have to wait until the data is analyzed to see how many tornadoes actually occurred.
This week’s forecast
A 1,038-millibar high about 300 miles off the Oregon coastline will move toward Whidbey Island while areas of high pressure build over the Great Basin and California.
This condition will produce night and morning gentle to moderate (8- to 18-mph) northeasterly (offshore) winds and weather that we normally expect for the midspring season.
Today will be enjoyable as temperatures should climb into the high 70s to the low 80s for most locations.
The high-pressure ridge will continue to build over California and temperatures will gradually warm each day this week, peaking Wednesday.
The exception will be the northwesterly-facing (Morro Bay, Los Osos and Montaña De Oro State Park) beaches, where fresh to strong (19- to 31-mph) northwesterly (onshore) winds will keep these areas cooler.
Overall, a week of great weather is in store.
A persistent ridge of high pressure in the upper-atmosphere will keep an omega-shaped storm track far to the north.
There is no hint of any rain in the long-term forecast.
Surf and sea report
This morning’s 5- to 7-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) will decrease to 4 to 6 feet with the same period this afternoon through tonight.
A 3- to 5-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) is forecast along our coastline Monday morning, turning to a 3- to 5-foot northwesterly (310-degree deep-water) sea and swell (with a 5- to 9-second period) as the northwesterly winds pick up along the coastline Monday afternoon and night.
This northwesterly sea and swell will further build to 5 to 7 feet (with a 7- to 11-second period) Tuesday.
A 5- to 7-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) is forecast along our coast Wednesday, decreasing to 4 to 6 feet Thursday.
Increasing northwesterly winds along the California coastline and a late-season 885-millibar Gulf of Alaska storm will produce a 6- to 8-foot northwesterly (290-degree deep-water) sea and swell (with a 7- to 15-second period) Friday through Saturday.
Friday’s moderate gale to fresh gale force (32- to 46-mph) northwesterly winds produced a great amount of upwelling along the coast.
Seawater temperatures will range between 48 and 51 degrees through Tuesday, increasing to 49 and 52 degrees Wednesday through Thursday.
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John Lindsey is a communications representative for Pacific Gas and Electric Company. He is a local weather expert. If you have a question, send him an email at firstname.lastname@example.org.