Description

The Washoe Zephyr is a thermally induced downslope wind which occurs across western Nevada, USA, just east of the Sierra Nevada mountains. It blows primarily in the summer from mid-afternoon until late in the evening from west to southwest, becoming quite gusty. As the terrain is generally arid, the Washoe Zephyr typically lifts a considerable quantity of dust into the atmosphere.

The zephyr begins within 2 hours of 2 pm local time. Maximum windspeeds are typically measured prior to sunset near Highway 395/Interstate 580, and usually diminishe by 9pm local. Peak sustained wind speeds can reach 20 kts.

Location

The zephyr wind develops along the eastern slopes of the Sierra Nevada and moves to the east across the Reno-Carson City area before weakening as it reaches the Carson and Humboldt sinks near the cities of Fallon and Lovelock.

Map of the Sierra Nevada and Great Basin showing the area most affected by the Washoe Zephyr circled.

Mechanism

The Washoe Zephyr runs contrary to the usual pattern of diurnal mountain slope winds (upslope daytime, downslope nighttime). The exact mechanism is still being studied but one likely hypothesis is that the wind is caused by intense heating over the Great Basin during summer afternoons. The heating causes a thermal low to develop which sets up a pressure gradient which induces the wind, pulling cooler air down from the High Sierra.

Flight safety considerations

Airports most affected include KRNO, KCXP and KNFL. The Washoe Zephyr plays a large role in the spread of wildfires in the areas affected. For further information, see the separate article on Wildfires: guidance for flight crews.