Reverse Sierra Waves

Reverse Sierra Wave (rSw) occurs when winds blow from the northeast over California, setting up standing atmospheric waves on the western slopes of the Sierra Nevada Mountains. This is the opposite of the classic Sierra wave, which sets up along the eastern escarpment of the Sierras in westerly winds. Kempton Izuno, of Lompoc, CA, wrote a 2-part article Soaring article about soaring easterlies, “Wave Cross-Country in Coastal California,” which ran in January and March, 2022. Here he braves the winter easterlies in the Sierra Nevada, rather than the Coastal Ranges.
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The frequency of winter cutoff lows has been increasing, creating more rSw soaring days; this article captures details from my recent flights to help us enjoy these conditions to their fullest, and avoid repeating mistakes.

Since our first reverse Sierra wave flight of Feb 12, 2023, my goal has been proving out this wave by going as far south as possible out of Williams, CA. On that first flight we turned around too early in S Yosemite. In 2024 I only flew one rSw setup, and we got stuck east of Lake Oroville; Ramy Yanetz did well on that flight. With a 50:50 win rate, I was keen to fly more rSw setups in 2025.

The early January 2025 rSw forecasts showed the wave extending to at least Mt. Whitney, if not further. The setups first appeared in late Dec for mid-Jan, so I kept my schedule open while working on the many ASH 30 projects at Williams Soaring Center (WSC). The first setup window was January 7-8. The seventh looked better, so I committed to flying with Michael Demeyer. The NNE wind was not optimal, yet the forecast showed plenty of wave (Figures 1 and 2). However, the forecast wave gaps and 500mb (18,000 ft) winds of over 90 kt made for very high risk if I missed a transition. In hindsight, this was not really a pure rSw setup, rather a mix of rSw and spot wave from the ridges running west off the Sierra.

We towed to a hotspot east of Lake Oroville, but could not get far going north. This is the third time I tried to go north from the Oroville start point, never getting more than a few miles. Now confirming over 80 kt winds, we abandoned that plan, left the lee of the Sierras at 17,900 ft to cross west over the Sacramento Valley with a quartering tailwind. We arrived at the Goat wave at 10,400 ft, climbed, tagged St. Helena and returned to Williams (Figure 3).

While not a distance success, we did confi rm the glider’s big new oxygen system worked, and that SeeYou Navigator did indeed cache Skysight weather data outside of cell coverage.

The January 8 forecast had more rSw, but with an almost straight northerly fl ow. Gordon Boettger considered joining us in his Arcus J from Minden for a straight-out mission south to San Diego. Gordo, a 777 FedEx captain, was fired up about the possibilities, but also circumspect due to POTUS TFRs in Los Angeles. After landing on January 7, we learned of the LA fi res, fanned by the same setup we planned to fl y, so we nixed the plan for the eighth.

The January 13 rSw setup was already on my radar, so I wasn’t disappointed with missing the January 8 setup.

To read the rest of the story, SSA members may log in from their desktop computer to SSA’s Soaring Magazine website and click on the May issue.