Weak Wave Days on the Wasatch

Weak Wave Days on The Wasatch

Much like sailing in light wind conditions makes the most skillful sailors, trying to hook into the wave and staying aloft on weak wave days challenges even the most skillful glider pilots. I had the opportunity to fly in weak pre-frontal wave here in Utah this November with York Zentner and Lynn Alley and came away with a much deeper understanding of this rare, but exciting lift phenomena.

Theory Vs Reality

My attraction to wave started years ago when as a boy I used to watch the huge lenticulars build up in the lee of the Sierra Nevada Mountains. These pillow shaped clouds, often times backlit pink and white into the fading twilight were fascinating to watch mostly because they were not moving! Looking across my desert backyard the winds on the ground were blowing every tumbleweed, speck of dust and maybe a few farm animals to the east end of the valley yet these clouds stayed in position as if tethered against the winds. Little did I know these clouds were forming and dissipating right in front of my eyes under the force of high winds and compression and decompression.

Fast forward to one of Lynn Alley’s PowerPoint presentations on wave flying, and it puts a lie to the notion that lack of movement in the atmosphere produces wave. As in a venturi , the high speed laminar flow of winds aloft provide one side of the ‘tube’ while the mountain ridge or peak provides the other side, compressing the air running up the ridge. As the air cascades over the lee side it accelerates down where the laws of stability force it to bounce and rise back up, causing the wave.

 

As Lynn points out, you don’t need blistering high winds to cause wave, just a steadily increasing wind profile of stable air at altitude and moderately unstable air at the lee surface to accentuate the downward sloping air parcel’s instability. We regularly experience wave behind the Wasatch Front with winds as light as 13 knots at ridge height and 25-30knots at FL180.  

The Art of Light Wave Flying

Now flying in moderate or strong wave can be exhilarating. Many high speed flights and at least two world altitude records have been completed in strong wave conditions behind the Sierra Mountains in California. (If interested, look up winter flying by club or region on OLC and you will see some remarkable speeds and distances flown.) And the risks can be daunting. Following the towplane through the rotor to the face of the wave can resemble a clumsy sword fight. One local story told about towing into strong wave has the glider pilot fighting to stay on tow with full scale deflections of the controls only to see the disorienting picture of the towplane upside down. At first the glider pilot thought he was upside down but No, the tow plane was inverted! A quick release was followed by the tow plane split S- away into the valley and now the glider pilot had to claw his way up the front face of the rotor into the calm of the wave.

All this high energy action of the winds can make for some serious sink! Nothing focuses the mind like seeing 1400 feet per minute sink into a twilight darkened mountain valley with limited land out possibilities!

Weak mountain wave on the other hand is a relatively gentle tow, followed by light to moderate turbulence getting through the rotor. Experienced wave tow pilot Stan McGrew (six decades as a pilot and CFI!) tends to find and use the lift along the front face of the rotor before dropping you off in steady wave. Tows can be long and expensive, however. Typically the front face of the wave starts around ridge height or slightly below. Ridge height near Morgan County Airport in Utah is nearly five thousand feet above airport elevation so plan to be on the rope for a while. 

Hawking the Weather

A small group of glider “Weather Weenies” (the name of a highly informative and humorous blog run by some University of Utah weather professors) monitor the fall and winter weather for wave potential. By e mail and phone we discuss 700mb and 300 mb wind patterns, wind profiles, approaching fronts. Who has time to follow sports when you have the whole western United States weather to monitor? Today’s weather looks marginal: Westerly winds at 14 growing to 20 at ridge height. A front that will brings snow to the mountains as I write this a day later pushes high thin clouds into the area but no moisture in the lower atmosphere to give us any lift markers.  Several of us decide to give it a try and pack as if going on a ski trip for the next day.  

On this mid November day Lynn Alley invited Kirk Urbanzyk to join him in his Duo Discus for a wave introduction. York Zentner brought his syndicate’s new DG505 and club member Paul McCoard. I had delusions of silver badge grandeur so I flew the club Twin Astir solo. My silver altitude or distance was not to be but a three hour lesson in wave technique taught by a couple of masters was ample substitute.

At 2pm we towed the gliders to the high end of the runway. Wearing thermal underwear and ski socks, we layered up with fleece sweaters, thin snow pants and light gloves. (One trick I thankfully followed: Trade your socks made sweaty by pushing gliders for a fresh pair right before launch. Staves off the inevitable cold toes for a little while.) Stan towed Lynn off as pathfinder and they found the wave close in right at ridge height. York followed and as I pre-flighted my glider I was dismayed to find the oxygen tank valve open and pressure at zero! One of the downsides of club glider operations! I made a mad dash down to the club oxygen cart and refilled the tank in time to get it back in and hooked up before Stan dropped the rope and returned for a landing.  Digital logger and barograph started (yes I am old school, it’s a perfect story for another time,) oxygen available, clock started, checklist complete and away we go.

As I climb on tow, Lynn and York chime in and start offering advice. Location of the lift, wind direction and speed at ridge and other traffic. Stan and I experience minimal turbulence through the rotor and we set up a steady climb. As we make one more pass along the short distance of rotor we begin to see a steady 600fpm up (tow plane averages about 400fpm) and Stan and I agree we are in wave. He parks me facing the ridge, I release and make a quick right turn followed by a left to face the wave again. York and Lynn chime in with “1-2knot climb” followed by Stan’s “Beats 1000fpm sink in the back of the rotor!” as he returns to the airport in our CallAir tow plane aptly named  “Ugly.”  

Sea Gulling

Now begins the patient work of maximizing lift in this weak wave. Fighting a tendency to fly too slow and increase the drag below minimum sink, I focus on flying 40-42 MPH and “bowtie” my way back and forth across the wave. Bowtying is Lynn’s description of marking the wave on your GPS or PNA so you can always return to where you know the wave is. Unlike thermals and ridge, wave lift rarely moves unless the wind conditions change significantly. This allows you to mark the lift and then translate back and forth off the starting point. If you fall into sink you simply get back to the bowtie and fill up on weak lift again-or fall out and head for the airport!

After twenty minutes of 1-200 fpm, I have drifted up to 11,500. Lynn and York in their higher performance birds have been up to 13,000 feet and translated 15 miles south and 10 to the north as I experiment moving up and downwind, left and right, to maximize the lift. After an hour of this and with nothing more than 1800 feet and 3-4 miles to show for it York and Lynn materialize, first on our new FLARM and then visually. They form up on my and then begin to lead me, farther and farther than my “comfort box” would allow. I mimic their distance from the ridge, accelerate with them over the lift gaps formed by canyons and make small course corrections to find and keep ourselves in the sweet spot of the wave.

As Lynn and Kirk slowly drift off to the north towards Mt Ogden, York goads me into following him back and forth behind the radar dome up on Francis Peak. “Keep up Gene, look I am hanging stuff out just to keep back with you.” Gear down, spoilers partially out the DG505 slowly drifts back towards me as I think “I’ve got to get better or at least get into one of those gliders!” Nothing beats years of experience but a few points of L/D can’t hurt! Multiple photo opportunities pass as I focus on formation flying with the DG.

York and I finally catch up to Lynn in the shadow of Mt Ogden and sea gull together over the parking lot of the Snow Basin ski area. Lynn reminds us that sunset tonight occurs at 510pm, just 20 minutes from now. We are staring into a weak winter sun through high cirrus but as I look to my left at our airport it is already in shadows and darkening fast. One by one we peel off to either explore the wave further north or run the face of the ridge before racing back to the airport for a twilight landing.

Thoroughly cold soaked, we put the gliders away in near darkness and discuss the flight. After a summer of booming thermals and high speed running this was a relatively low “numbers” day. My barogram trace later showed I had stayed in an altitude band of only 2,500 feet and my digital track showed I only strayed from our airport by about 18 miles. But nothing beats palling around for two and a half hours at 11,000 feet in weak wave.

Before the snow berms get too high on the side of the runway to fly safely we can expect 2-3 more fronts to push through and give us more wave days, hopefully with rotor and lenticular markers. I am not sure I could sit through 5 hours of -10C temperatures at altitude to finish the silver badge but the beauty and challenge of wave soaring is “Anything is possible.”