Santa Ana winds return to California

Last week, strong winds were reported across portions of Southern California that led to the explosive growth of a major wildfire, known as the Franklin Fire, in Malibu. As of the weekend, it had burned more than 4,000 acres and either destroyed or damaged over 40 structures. Many well-known celebrities had to quickly evacuate their homes due to the rapid spread of the wildfire.

The strong ridge of high pressure locked in over the West helped to create very strong winds in Southern California. Many of us know about the “Santa Ana” winds that were generated as winds were gusting up to 80 miles per hour. A Category 1 hurricane has a wind speed of 74 miles per hour.

With the big high-pressure system situated over the interior portions of the western states, there is lower pressure over the Pacific Ocean. When there is a big difference in air pressure, winds will rush from high to low. In Southern California, the air gets funneled through the canyons and passes and becomes stronger. The passes include the Soledad Pass, the Cajon Pass and the San Gorgonio Pass.

The Santa Ana winds are typically a drying wind as they move down from the mountain to the lower elevations. The down-slope winds dramatically lower humidity levels and raise the temperature. The dry air mass has sent relative humidity levels down to nearly 10% as the warm air mass and the high wind speeds will usually dry out the vegetation making the region vulnerable to these wildfires. They can occur at any time of the year but are most common from September through May during the cooler months of the year.

Some of the strongest Santa Ana winds ever recorded happened in December 2011. The cities of Pasadena and Altadena in the San Gabriel Valley reported “sustained” winds at 97 miles per hour. That was the equivalent of a Category 3 hurricane. There was a wind gust of 167 miles per hour which knocked down thousands of trees, and power was out in parts of that area for over a week. In addition to Southern California, the winds were also very strong in Utah. Mammoth Mountain reported a wind gust of a whopping 175 miles per hour Dec. 1, 2011.

Across the Pacific Northwest and the North American interior, mainly the Canadian Prairies and the Great Plains, western winds are often referred to as “Chinooks” or “Chinook winds.” These winds are mostly winds from a westerly to southwesterly direction across the Pacific Northwest and are generally seasonally wet and warm from the Pacific Ocean. They will often deliver huge amounts of rain to the lower elevations with heavy snow in the mountains.

The Chinook winds are also used for “fohn” winds across the interior locations of the Northwest and Great Plains. Areas that are the eastern slopes of the mountains will experience these winds from the same direction, but, like the Santa Ana winds, become warmer and drier as they descend from the mountains to the lower elevations. A strong fohn, or Chinook wind, can force temperatures to rise up to 60 degrees in a matter of hours or days.

According to weather records, east of the Black Hills in South Dakota, the biggest temperature rise in two minutes happened in Spearfish, S.D., on Jan. 22, 1943. The thermometer went from -4 degrees to 45 degrees Fahrenheit, an incredible rise of 49 degrees.

The direction of the wind will play a big role in the weather here in North Idaho. Thanks to a southwesterly flow last Saturday, the high in Coeur d’Alene soared to an above-normal 48 degrees.

In terms of our local weather, we’re expecting rain and snow through Tuesday with mostly rain on Wednesday in the lower elevations. The weekend storm also looks warmer with rain in the valley locations.

The Pacific Northwest is in a pattern with warmer storms moving into the region when the high-pressure system weakens. The colder air has been funneled to the northern regions east of the Rockies. In fact, heavy lake-effect snows have been reported in Upstate New York where “feet” of snow were piling up.

The long-range computer models continue to show occasional rain and snow through the end of the month. There’s also the possibility of some light snow near Christmas Day with a better chance of snow at the end of the month. There is still hope for more snow early in 2025 as sea-surface temperatures near the equator have been cooling. Over the last 3-6 weeks, the ocean waters in this region were getting warmer, which often led to less snow in our region.

This October through mid-December period in North Idaho has been one of the most snowless in history. However, with these crazy weather patterns, for those wanting snow, perhaps conditions will change soon.

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Contact Randy Mann at randy@longrangeweather.com.