Nevada town is key to predicting winds that can cause fires
Winnemucca is not only home to the Buckaroo Hall of Fame. The arid town of 7,400 in the Nevada high desert is a critical weather beacon that helps meteorologists predict dangerous Diablo winds that often spur devastating California wildfires.
The “oasis in the desert” is once again front and center this weekend as forecasters, using calculations from Winnemucca’s airport, have determined that a massive wind storm is headed to the greater Bay Area, leading Pacific Gas and Electric Co. to prepare to shut down power to a couple million people starting Saturday.
The forecasts show patterns similar to those that yielded winddriven fires in Wine Country on Oct. 8, 2017, that killed 44 people and destroyed 8,900 buildings. Why Winnemucca? “It’s almost dead center in the highpressure area,” said meteorologist Jan Null, who helped coin the term Diablo winds after the phenomenon led to the deadly 1991 Oakland hills fire.
Warm and dry Diablo winds originate over the high deserts of the Great Basin. They blow when cold, highpressure air over the region runs in contrast to lowpressure systems near the Pacific Coast. As the winds move from the deserts across the Sierra Nevada, they rush downhill, gaining heat and speed as they approach the ocean.
The best indicator for such an event is the “pressure gradient,” basically the difference in atmospheric pressure between the two areas. Generally, the larger the difference, the stronger the wind speeds.
Calculations are pulled from San Francisco International Airport and Winnemucca Municipal Airport. The Nevada airport reading is preferred because it calculates sealevel pressure, providing an applestoapples comparison to SFO.
Several historically damaging wildfires with high winds have emerged from large pressure gradients.
On Oct. 20, 1991, the pressure between Winnemucca and San Francisco was minus 13.1 millibars as fire tore through the Oakland and Berkeley hills, killing 25 people. It reached minus 17.8 millibars during the North Bay fires on Oct. 8, 2017, and minus 16.3 millibars during Thursday’s Kincade Fire in Sonoma County.
One weather model for this weekend shows a pressure gradient reaching about minus 17 mb across the Bay Area, Null said. A big caveat is that the exact location of the Great Basin high and the offshore low can impact wind speeds and direction.
“It also depends on the flow over the mountains,” Null said. “This weekend is going to be a real strong wind event, but the real question is will the winds get down to the surface to populated areas.”
Winds along ridges and mountaintops spur fastmoving blazes. However, what can take a fire to the next level is winds blasting through residential neighborhoods at sea level.
The angle of the winds flowing over the mountains also can determine wind speed, Null said. The more direct and perpendicular that winds strike the tops of ridges, the faster they flow downhill and warm up.
Highpressure patterns that sit over Winnemucca and the Great Basin are most common in the fall and winter months as the jet stream sinks south. If that highpressure zone moves farther south, it can create Santa Ana winds in the southern portion of California.
The timing of Winnemucca’s highpressure system couldn’t be worse. California’s Mediterranean climate includes a long dry period, ending in late fall. And as the climate warms, the fire season has extended.
The result is an event like this weekend’s, in which competing atmospheric pressures create fast, warm winds ripping down mountain ranges into grasses, shrubs and forests at their driest moments of the year.
So, as you light a candle to illuminate your home this weekend, and as you listen to your patio furniture howl in the gales, you can thank the highpressure system planted above your Winnemucca friends as they enjoy this weekend’s Fall Farm Festival.