In a classic Nina model, the storm’s track was centered over the Pacific Northwest for much of the meteorological fall (September through November).
As a result, a series of low pressure systems and associated atmospheric cold fronts / rivers produced record precipitation throughout the Pacific Northwest. Seattle-Tacoma Airport reported 19 inches of rain in this wettest weather drop on record. Not to be outdone, Abbotsford, BC, had the largest with 33 inches of wet material, shattering previous records and causing extensive flooding.
On the other hand, the predominant weather feature off the California coast during November was the Eastern Pacific High. In the summer, clockwise circulation around this high brings cooler air from the Gulf of Alaska, often producing a lingering marine layer along the west coast that reduces the need for air conditioners.
Like summer, this fall saw the Eastern Pacific High anchored off the California coast, keeping the southern branch of the polar jet, high winds that cause storms, well to the north.
Combined with the eastern Pacific high, transient high pressure systems over the Great Basin – the area between the Sierra Nevada range in the west and the Rocky Mountains in the east – created persistent northeast winds. of Santa Lucia.
These winds produced clear, dry skies with cold mornings and warm afternoons. In fact, many daily high temperature records were broken during the last week of November.
Typically, the San Luis Obispo County Airport registers 1.4 inches of rain in November; however, last month saw only 16 hundredths an inch of rain. Santa Maria Airport reported 11 hundredths or 10 percent of the historical average for November. Paso Robles Airport was parched in November with a meager hundredth of an inch.
November temperatures were much warmer than average; the average temperature at San Luis Obispo airport was 63.2, the second highest on record. Santa Maria Airport saw an average of 60 degrees or 3 degrees above historical averages. Paso Robles Airport was 5 degrees above normal, averaging 57.9 degrees. Interestingly, the hottest November on record at these airports was in 1949.
This December, a significant change in weather conditions occurred with the storm door opening wide. So what does this mean?
The eastern Pacific high acts as a massive roadblock, pushing the storm’s track further north. This week, the eastern Pacific high will move 2,500 miles northwest of California, allowing high altitude winds to move southward and target California directly. In other words, the door is open to storms.
These high winds will bring a series of storms and associated cold fronts from the Gulf of Alaska to California from Monday to Tuesday, and possibly longer.
This condition is expected to produce moderate to cool gales (32 to 46 mph with gusts to 55 mph), southerly winds, moderate to heavy rains, and heavy mountain snowfall above 4,500 feet. from Monday to Tuesday. Between 2 and 4 inches of rain is expected with higher amounts along the coastal mountains.
A colder weather system will bring more rain and mountain snow on Thursday or maybe Friday.
Believe it or not, this weather model was predicted almost two weeks ago by the new and improved version of the National Oceanic and Atmospheric Administration’s Global Forecasting (GFS) model, also known as the American model in the community. weather forecasts.
This leads to the question, why did the Eastern Pacific high move well northwest and open the storm door?
Currently, no one knows for sure. Perhaps the arctic vortex has split into three sections, helping to move the eastern Pacific high well off the California coast. This condition may continue to help direct storms to California.
Another low pressure system is expected to produce gusty winds, cool temperatures and low level snow on Christmas Eve. However, there is no guarantee when trying to predict so far into the future.
The storm on Monday and Tuesday is expected to be the strongest of the season so far.
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John Lindsey is a meteorologist for PG&E.