One if by thermal, two if by wave, three if by ridge lift

by: William R. Cotton

For years now Ward Hindman and I have talked about going soaring in the Grob-109B motorglider which I have a 1/4 share in. Ward is an M.S. graduate in Atmospheric Science at CSU eons ago BBC(before Bill Cotton), and later worked as a research associate in the department for a number of years. During his time spent in the area Ward flew sailplanes out of the former Waverly Gliderport and at Owl Canyon when Fred Herr operated it and later as a CSA member. So, he is quite familiar with soaring in the area. Ward is now a faculty member at the City College of New York in meteorolgy and soars the east coast corridor.

In August Ward E-mailed me that he would be in Colorado 1-7 October and would like to give it a try to go soaring. On the 29th of September I E-mailed him that my schedule was pretty open on 2 October in the afternoon and the long range forecasts looked promising for decent thermalling. So, I scheduled the Grob from 12 to 4PM, and hoped that the weather would cooperate. Putting two meteorologists in the same plane was really asking for the weather gods to attack!

On the morning of 2 October I had a 9:00AM class, so by 6:45AM I was busy in my office copying class notes and preparing a weather briefing which I present the the first 10 minutes of class. This was ideal preparation for the planned afternoon flight because I was forced to do a thorough meteorological analysis of the weather at the time. It indicated that a trough of low pressure with attendant surface front was approaching Colorado from the northwest. It was not predicted to move into the Front Range until the following day but as it approached the winds should become southwesterly and increasing in strength. No Denver sounding was posted on the web so I had to examine the Grand Junction and Grand Island, Nebraska. They suggested that there should be sufficient instability for decent thermalling.

I checked with the Denver FAA soaring forecast and they were only giving a wave soaring forecast. This is because they make the bureaucratic decision to only give a wave soaring forecast after 1 October and only a thermal forecast for the summer. This is ridiculous because nature knows no calendar and thermalling or wave soaring could occur most any month of the year around here. Anyway, their wave soaring forecast was poor. This didn't jive with my experience as I have found that whenever the winds are southwesterly and reasonably brisk and not favorable for deep convection, the wave potential along the Front Range is high. This is because the Front Range is oriented north-northwest to south-southeast, so that if the upper air flow is from 300 degrees to 220 degrees, it is nearly perpendicularly to the barrier. Flows 300 degrees and north provide a small barrier-normal component so that even if lenticulars are visible, the base of the wave is above 20,000ft MSL.

I also had an interest into motoring over to the Medicine Bow Range, as I have had some excellent ridge soaring experiences in the region north of Cameron Pass and south of Wyoming. I hadn't been up there this year and with the southwesterly flow aloft, the opportunities for ridge soaring should be excellent.

Ward and I met at the Fort Collins Loveland airport about 12:30 and after putting a pretty good load of fuel aboard to get to the Medicine Bow Range and back, we motored off to the foothills. Before reaching the hills we cored into some pretty strong thermals, allowing us to shut down the engine and feather the propellor. We worked our way up to 9,000ft in them and headed over the ridge that includes Horsetooth Rock. I gave Ward the controlls and he started to get the feel of the plane. He said the controlls felt light and it turned spritely. He had a little harder time staying with the thermals in a right turn compared to a left turn which really bugged him. Working these thermals we got up to about 13,000ft. The foothills to the north of Horsetooth are great fun to soar with nice views over the ridge itself, and Redstone Canyon immediately to the west and Rocky Mountain Park visible further west. To the east is Horsetooth reservoir and the city of Fort Collins. As long as one stays high or on the eastern side of the ridge it is a very safe place to fly as Christman Field is in easy gliding range. Low over the western side would put you into Redstone Canyon which has few safe landout options.

Thirteen thousand was not enough altitude to head west into the next set of clouds across Redstone. There was also a big blue hole to the northwest. Besides heading up to the Medicine Bow that way is very dangerous as there are virtually no landout options until North Park, a long ways upwind. So, we elected to follow the cumulus road north along the first foothills range. I thought maybe we could cut west along the Cheyenne Ridge bridge into the high country. But, as we got north of the Red Feather Lakes road just south of the Wyoming border over Highway 287, the thermals became increasing broken up and turbulent. 13,000ft was as high as we could get which was not enough to get us over the higher mountains to the west.

Nonetheless, since we had an "iron thermal" aboard, we headed west into the teeth of the wind. Ward said that this was like flying a 1-26! We were sinking faster than our headway would allow us to catch the next line of cumulus. Penetrating with the Grob at airspeeds over 70kts is like soaring a D-9 catapillar! At 2000AGL I cranked up the engine, with an eye on Dan Miller's fields as an option if the engine didn't start. Ward remembered landing out there a long time ago.

Moving westward at an indicated 70kt airspeed, we appeared to be making only 40kts over the ground. Occasionally we would encounter cloud regions with good lift but this was more than compensated by the major sink between cloud bands. It was becoming increasingly evident we had wave aloft, but these clouds really had us confused. They didn't have the ragged appearance of rotor clouds, more like normal cumuli, but they did have a rough linear alignment to them. Beneath them the thermals were all broken up, feeling more like rotors.

We continued under power west, slowly working our way over Deadman Pass, across the Laramie River Valley, over Shipman Park, and then at a rip-roaring 25 to 30kt ground speed finally made it to the west side of the Medicine Bow Range. I shut down the engine, feathered the prop and headed south crabbing along the ridge. Ward and I took turns working the ridge back and forth. The views were nothing short of spectacular! As we headed south, sometimes with the left wingtip pointed at the alpine meodows, sometimes ascending to 13,500ft or 1500 to 2000ft above the peaks, we could see the cirques with snow fields, Clark Peak, and the alpine lakes such as Iceburg lake. Off the right wing we could look down the escarpent 2000ft below and see aspen forests at the peak in fall colors.

The highest we could get in ridge lift was only 13,500ft which was not enough to make it across the valley to the ridge to the east, since the sink was severe. So we turned on the engine and motored to the next line of clouds over Deadman. Ward tried to see if we could get enough lift on their western side to kick us into wave. But, it was not to be. So we continued east until we got to the next line of cumuli. There I worked their windward side under power seeking that elusive wave lift. Then it happened! The varios started climbing with the audio vario going T-T-T-T at a rapid cadence. I shut down the engine and up we went, pegging the varios at 5m/s. In just a few minutes we smoothly and quietly ascended to 18,000ft, over shot a few hundred feet, and I put the nose down and headed along the cloud line to the south. The cumuli extended to at least 22,000ft so I had to find a big enough break in the towers to make our cut to the east. I find soaring next to a line of cumuli as attractive as soaring next to a mountain ridge. The cumuli have this bright hard appearance that is reminescent of a snow-covered mountain range with even more orography! It reminded me of my days as a meteorological observer on research aircraft such as as NOAA's DC-6 and C-130, and especially the Australian CSIRO DC-3. The latter plane was equipped with an observer glass bubble in which I stood and directed the pilots on penetration of the cumuli. It was always a thrill to approach those towers and penetrate into what visually looked like plunging into a mountain!

These were clearly not rotor clouds but cumuli beneath the wave that were penetrating well into the wave itself. Weaving our way around the cumuli in this wave-related forcing, we finally found ourselves free and clear still at 18,000ft. We were probably 50 miles due west of Owl Canyon Gliderport and 65 miles from Fort Collins-Loveland Airport. We then took a long sled ride back to Fort Collins Loveland, with a little purpoising action along the front range ridges, arriving there still some 2000ft above pattern-entry altitude. This gave Ward some time to practice improving clean right turns.

The last few times I flew the Grob, my landings were rather bouncy, getting a few touch and goes in! This is probably because I had gotten quite a bit of time in the much lower sitting PIK20E lately. This deadstick landing was a three point kiss-on followed by a perfect roll out into the highspeed taxi way, whereupon I started the engine. What a way to end a perfect flight! Total time 3:40 minutes with over two hours power off time. Most of the engine time was plowing our way over to the Medicine Bow Range.