March comes in like a lion, they say — and the weather will be wild come March 1.
An atmospheric river is expected to bear down on the county from Friday night into Saturday, with another one arriving early next week. Rainfall amounts with this weekend’s system are forecast to range between 1 to 2.5 inches, according to PG&E meteorologist John Lindsey.
Scattered rain showers are expected Sunday morning, Lindsey said, before a break in the weather from Sunday afternoon into Monday.
Another heavy rain storm is expected from Tuesday into Wednesday, according to Lindsey. The Central Coast could see another 2 to 3 inches of rain on Tuesday and another inch on Wednesday.
“Tuesday looks like a lot of rain,” Lindsey said.
Rainfall amounts from Saturday into Wednesday could range between 3 to 6 inches total, Lindsey said. There’s even more rain in the forecast after that.
“If this much rain happens, that should push most locations over their yearly averages,” Lindsey said.
A 3-day storm cycle
“It appears the Central Coast may have entered into a classic 72-hour storm cycle, with a new low-pressure system developing every third day,” Lindsey wrote in an email to The Tribune.
Over the phone, Lindsey said he doesn’t know why the pattern exists, but he’s noticed it through long-term observations of weather in the area.
“Historically, when you see a blocking high in the Gulf of Alaska, you get into a 3-day cycle,” Lindsey said.
A “blocking high” is an area of high pressure that blocks the jet stream — a band of strong wind in the upper levels of the atmosphere — from going north, and pushes it to the south. That causes the jet stream to pass over the Pacific Ocean.
A pattern like that is rare, Lindsey said.
“That’s a sure signature of a wet year because it could last for a couple of months and that’s when you start really bringing up those rainfall totals,” Lindsey said.
Will there be another chance for snow in SLO?
The storm systems forecast from March differ from the snowier systems we saw in February because they’re coming over the Pacific Ocean and not down from the north.
When the system goes over the ocean, it picks up more moisture, which means the storms tend to drop more rain and snowfall levels are higher, Lindsey said.
The cold storm system we saw last week came down the West Coast from the Yukon over land, so it didn’t hold as much moisture. The system was, however, really cold and dropped the snowfall levels down low.
“They’re both wet weather patterns but so different from each other,” Lindsey said. “Instead of brother and sister, they’re more like cousins.”
A freezing month
Colder storm systems helped push February’s average temperatures lower than normal.
As of Feb. 26, the average high temperature at the San Luis Obispo County Regional Airport was 57.5 degrees — 7 degrees cooler than the normal average high of 64.1 degrees, Lindsey said.
The normal low in February is 42 degrees, but this month it’s been 38 degrees, Lindsey said. He cautioned that the last few days of February, which have been mild, could bring up that average.
That’s a contrast to the months before: this January, with an average high of 63.9 degrees and average low of 43.2 degrees, was warmer than the normal average high of 63.6 degrees and average low of 40.7 degrees, according to Lindsey.
December 2018 was average, but November 2018 saw average high temperatures of 74.9 degrees — about 4 degrees warmer than the normal average high of 70.1 degrees — and an average low temperature of 45 degrees, up from a normal average low of 44.2 degrees, Lindsey said.
“It happens, sure, but not that much,” Lindsey said of February’s chilly temperatures, adding that December 1990 was one of the more notable recent times that freezing temperatures hit SLO County.
How long will the wet weather last?
It’s too soon to say how much longer SLO County will see wet weather, Lindsey said.
Another storm is possible on March 10 and 11, but after that it’s a big question mark.
The weather looks wet for the foreseeable future, Lindsey said Thursday.
“The latest model runs indicate that the wet weather pattern will continue,” Lindsey said. “This (forecast model) is going all the way out to the 15th and not showing any significant breaks in rainfall.”
Lindsey cautioned that he’s looking at long-range forecast models which are subject to change.
“I’m not saying that’ll materialize, but I think there’s a good chance of rain every single day,” Lindsey said. “It looks like rain almost every single day, especially Tuesday and Wednesday.”