Diamond Goal in 2 Hours 34 min

The soaring forecast for this past Saturday suggested strong thermals along the lower foothills but strong westerly winds – and therefore much more difficult conditions – on the west side of the Continental Divide.

Here are some of the key weather charts that I looked at the night before my flight:

Strong thermals of 3-4 m/s (6-8 kt) along the foothills from Colorado Springs in the south to the Colorado/Wyoming border in the north.
Thermal height at 2PM – quite high – to be expected for the mountains but higher than usual for the plains along the foothills. Cloud bases near the legal limit of 18,000 or even higher mean that much of the flight can be high above the terrain and therefore stress-free, with a wide glide radius and therefore a wide range of landing options as long as one can stay in contact with the clouds.
30+ knot winds to the west of the Continental Divide (at the top of the boundary layer)
Modest risk of overdevelopment north of Boulder but no risk of thunderstorms.
The net result presented in the PFD chart: strong thermals, a high base, and not much risk of over-development = strong attainable flight distances, especially along the lower foothills.

Plus, very important to look at, especially in Boulder, is the convergence forecast.

Projected convergence (and divergence) lines at 2:30PM.  The chart shows several convergence zones along the lower foothills. These are super helpful especially when they are marked by curtain clouds and/or different cloud bases. In blue conditions a situation like this can be confusing for the pilot as it is not possible to see why there is lift in some areas (where air masses are coming together, i.e. converging) and sink in others (where air masses are drifting apart, i.e. diverging).
Convergence forecast for 4PM. This shows a very pronounced line along the lower foothills. It is particularly useful to look at the projected development of convergence lines over the entire soaring day. (Just as it is important to look at the development of thermal height, depth, and strength). Skysight makes this easy to do by pressing on the triangle icon to the right of the time slider.  Note, however, that there are so many variables at play that it is impossible to predict precisely where the convergence zones will be at any given point in time.  Especially this part of the forecast can only be directional at best.  However, I have found it to be extremely useful in forming a mental picture of the potential movements of air masses throughout the day. By reading the clouds it is then much easier to understand what is going on and to adjust accordingly.

Given these conditions I decided I would stay on the east side of the divide and plan a pre-declared 300km triangle route that would take advantage of the strong thermal conditions along the lower foothills as well as the convergence lines.  If the convergence forecast would hold and if I did my planning right, I might even be able to fly relatively fast and get some points for the OLC speed league as well.

With these objectives in mind, I declared the following triangle that would meet the requirements for a Diamond Goal Flight according to the FAI.

Start at Gross Reservoir Dam.  I wanted the start to be within a 15 km radius around the Boulder airport since you have to fly through this cylinder after getting off tow to qualify for OLC speed league points.  Gross Reservoir is just within the 15 km mark.  It is also on the west side of the Flatirons, where thermals tend to start much sooner than on the east side where the inversion can be very persistent. Another advantage is the fact that the south-tow route from Boulder runs along Eldorado Canyon, just a little south-east of the reservoir.  (When towing north, a good alternative start point within the 15 km cylinder would be Bighorn Mountain.)

First TP at Halligan Reservoir, 103 km to the north of Gross Reservoir.  According to my forecast, the convergence line would likely be a few miles east of Halligan.  There were two reasons I wanted to stay on the west side: 1) the lift tends to be much weaker once you get into the more humid air mass that typically lies east of the convergence; and 2) the cloud bases on the east side are often much lower.  The last thing I wanted was to be forced to descend down low just to round a turn point and then have to work my way back up.  I also considered moving the TP further north but the mountains get lower the closer you get to the Wyoming border and this often means that the prevailing westerly winds tend to be stronger and therefore the thermals weaker and less organized.

Second TP at Conifer, 151 km to the south of Halligan Reservoir.  The projected location of the convergence was, once again, among my top reasons to pick Conifer.  It also has the advantage of being less than 60 km away from Boulder, which means that given the forecasted height of the cloud base around 18,000 feet, it would be well within final glide range of the Boulder airport. I therefore considered it a stress-free turn point even if the conditions would be less than ideal.

Finish back at Gross Reservoir Dam, 48 km to the north of Conifer, for a total triangle distance of 302 km (164 nautical miles).

Task as shown on Google Maps

I knew, of course, that reality never exactly matches the forecast.  To prove this point, as I drove to the airport in the morning, a long and wide lenticular cloud shielded the sun from reaching the ground along the foothills over a stretch of at least 100 miles.  The temperature at the airfield was pleasantly cool but this only meant that without direct sunshine, thermal activity would start much later than 10:30AM as projected in the forecast.

However, given that it was June 22 – just one day beyond the summer solstice – there was a lot of daytime left for the lennie to disappear and for the day to develop.

Around 11:30AM the cirrus shield had become noticeably smaller and thinner and the temperature on the ground started to rise quickly.  The more impatient pilots decided to launch, unfortunately only to return to the airfield 20-30 minutes later.  Clearly, it was still too early.   I kept telling myself that there was no reason to rush.  Sunset was at 8:34PM and thermal activity would likely last until well past 6PM.   And my task should not require more than 4 hours,  maybe even considerably less.

I decided to remain on the ground until the first pilot would stay air born.  That was the case around 12:30PM.  I waited for one more pilot to launch and finally took off just before 1PM.

A beautiful cumulus cloud had formed right above the Flatirons – ideal for a south tow towards my start point.  I stayed on tow probably a little longer than necessary and released in the second good lift at just under 10k feet MSL.  My climb rate immediately improved once I was off tow – funny how that works – and within minutes I was up at 15k feet and ready to get on task.

There were some nice looking cumuli right along the task line interspersed with some blue gaps in between.  The first gap was perhaps the biggest at about 15 miles but I wasn’t bothered by it.   I had enough altitude and the cloud ahead looked very promising.  I was also within glide range of Boulder and knew that in the worst case I could try again.  I also saw some developing wisps along my path and slightly adjusted my route by a few degrees here and there to take advantage of any rising air, always staying slightly on the upwind side.

Beautiful skies on my first leg. The town of Estes Park is below. Longs Peak is on the left side of the picture just below the wing. I just left a very strong climb and am heading north towards Halligan Reservoir.

A very powerful climb near Estes Park (up to 15 kts average!) took me to 17,000 feet and another over Signal Mountain to 17,500.  The path forward to my first TP was along the convergence zone:  generally the air was just rising up by 1-2 kts and I was able to fly in a straight line while maintaining altitude as long as I wasn’t pushing for speed.

As I got closer to Halligan Reservoir the cloud base dropped a little so I flew a bit faster to come down as well, rounding the turn point at an altitude of 16,000 feet.

Rounding the first TP over Halligan Reservoir

Looking back to the south after my 180 turn, I noticed the convergence had continued to develop and the line was now better marked.

A few miles after rounding TP1, heading south. The convergence line is clearly visible and the cloud bases ahead are rising. Horsetooth Reservoir is visible 20 miles ahead in the distance, approx. 20 degrees left of the nose. There’s a long paved private airstrip (“Christman Field”) just east of the northern tip of the lake, probably the best land-out option in this area because you could just get a tow plane instead of having to trailer back. However, with skies like this in front I was not at all worried about having to land out.

West of Ft. Collins I stopped to get back to over 17,000 feet before continuing my convergence surfing:  the line wasn’t completely straight so I curved gently along its west side, flying faster in sink and slowing down in lift, for the most part able to avoid any thermaling.

Well-marked convergence line on my second leg, heading south. The low hanging curtain clouds mark the boundary between the different air masses. The air on the drier side (where the cloud base is significantly higher) is rising. When you see clouds like this just fly along the curtain clouds and stay on the side with the higher cloud bases. It works!

West of Golden, the convergence line made an obvious turn toward the west so I decided to make a little detour as well:

You can see my detour to the west on my second and third leg as I followed the convergence. The straight line between Gross Reservoir and Conifer is the task direction. My flight path curved west via Squaw Mountain as I flew along the west side of the curtain clouds that marked the convergence. If you look closely at the slight change in color of the flight trace, you can see that I gained altitude between Gross Reservoir and Squaw Mt. on the southbound leg. At Squaw Mt. I had to leave the convergence line to reach Conifer 20+ km further SE. You can also see my altitude drop (the trace line changes color from blue to turquoise) as I tug underneath the lower cloud base near Conifer. After rounding the turn point I first headed WNW instead of flying straight towards Gross Reservoir in order to follow the best available energy line. Although this meant a longer flight track it was likely still faster than going straight and stopping in (likely weaker) thermals along the way.

Conifer lay about 10 miles east of the convergence requiring me to temporarily leave the air mass that had carried me so well.  Once again I had to drop down to about 16,000 feet to make the turnpoint and stay clear of the clouds.

After rounding Conifer, I headed right back toward the convergence line, following along a ridge towards Mt Evans where the air was slightly ascending which meant I was also to get back to the convergence without losing much altitude.  Near Squaw Mountain I stopped in a thermal to top up to 17,700 ft and from there it was a straight glide to the finish line over Gross Reservoir.

Steep celebratory turn over Gross Reservoir just after crossing the finish line :-). You can see the dam straight below.

A glance at the flight computer told me I had completed my 302 km task in just 2 hours and 34 minutes.  That equated to a respectable average task speed of 118 km per hour.  I’m sure an experienced XC pilot could have shaved off another 20-30 minutes but I’m definitely happy with this result for my fist 300 km goal flight. (I even arrived 1000 feet higher than I had started out!)

My flight computer happily announced that the task was indeed finished. Average task speed 64 kts (118.5 kph)
The red line shows my route on task. The blue line is my flight trace before and after the task portion.

With my task completed, I wondered what I could add-on to enhance my OLC score.  I thought it would be great if I could turn my overall flight track into into a big FAI triangle.  To do that I would have to cross the Continental Divide and fly west to a point roughly perpendicular to the line between Halligan Reservoir and Conifer, and approx. in the middle of it.  Kremmling, I thought, would be an ideal turnpoint to shoot for.  If this worked I might be able to post a 400 km FAI triangle.

The first practical question was how to get to the Divide.  The straight line west from Gross Reservoir did not look promising as it meant pushing into a big blue hole against a 15-20kt headwind.  There were no clouds for 20 miles and I expected a lot of sink in the lee of the mountains.  Quick decision: I would return towards Mt. Evans where the convergence line had already proven to work – then I would fly north along the divide and look for a cloud street that could take me west.

In trying to execute this add-on plan, the first part worked well.  Within 20 minutes I was on the divide near Silver Plume Mountain.

Above the Continental Divide near James Peak, looking SW towards Vail. This cloud street looked very good but it wasn’t exactly in the direction I was most interested in taking. Also, the clouds were now developing very rapidly with the first virga are already visible on the horizon. Lastly, I am still not sufficiently familiar with the land-out options in this direction so I did not seriously consider taking this route.

As I continued to head north along the ridge I hit significant sink.  I stopped at Mt. Flora to get back to 17,500 before a blue gap to the next cloud near Mt. Jasper.  There I only found a very weak climb in turbulent conditions.

Unfortunately the clouds to the west of the divide were now rapidly over-developing.  As I circled around Mt. Jasper I could see more and more virga and rain showers developing in the direction I wanted to fly in and so I decided to shelf my FAI triangle plan for another day.

Continuing along the divide also seemed pointless as the thermals on the ridge were weak and extremely wind-blown. The convergence over the foothills still looked promising, however, and so I headed back towards Gold Lake.  With the wind from behind this was a quick transition but I still lost quite a bit of altitude flying through the lee side sink.  I had been right not pushing into the wind earlier.

Leaving the Continental Divide heading east. The wing points north along the Divide. Niwot Ridge, Left Hand Reservoir, and Brainard Lake are visible below. Longs Peak and Mount Meeker are clearly visible in the distance. The blue skies above are indicative of the lee side sink on this side of the mountains.

A mediocre climb near Jamestown (I wondered: would I have taken this had I been trying to get somewhere?) took me back to 17,000 and a vicious rotor over the Twin Sisters (i.e. in the lee of Longs Peak) brought me to 17,500 feet.  From there I tried to connect with the clouds on top of Trail Ridge Road to maybe push a little further west from there.  However, by now I should have known better than to approach the Divide from the lee side on such a windy day.  After hitting heavy sink I scrapped that plan as well and headed back to the tried and true convergence line north of Estes Park. By now overdevelopment set in almost everywhere around me and although the lift was still strong, the lack of sunshine in the cockpit meant I was getting cold.

Estes Park viewed from Triangle Mountain around 6PM. There’s still a nice cloud street to the west of Estes Park but it is too late for new adventures on the other side of the divide. Also, the amount of virga and rain showers is rapidly increasing at this time.

With 6pm approaching the next decision was simple: enough for the day.  I started my final glide north of Estes Park, flew straight to Golden and from there back to Boulder where I arrived with plenty of altitude to spare.

Flight stats.

My total flight distance ended up being 523km.  So in addition to Diamond Goal I also completed Diamond Distance.  And my bonus goal of earning OLC Speed League points for our club worked out too.  With 118 points I scored second for SSB this past weekend and first among those flying from Boulder. The flight track is here.

Evening scenery at the Boulder airfield after a great day of flying.


Lessons Learned

  • Careful task planning can pay off.  Usually a pre-declared route should mean a lower average speed than simply following the best visible lines.  However, by carefully planning my task in accordance with the thermal and convergence forecast I was able to pre-plan the flight in a way that took advantage of the best projected energy lines.  And since the reality was not very far off from the forecast, requiring only a deviation of about 20 miles or so, I was able to complete the task as quickly as I did.
  • Flying with a specific goal in mind greatly focuses in-flight decision making. On previous flights when I took off without a specific objective in mind, the choices were endless.  This meant I often took a while to make up my mind and I also found myself reversing decisions I had made simply because small changes in the sky momentarily made some other direction look more promising.  This Saturday I had a clear goal and all my decision were made to safely get to the goal as fast as possible.  The difference this makes to the thought process is amazing. At any given point there are much fewer choices available and I’ve found myself homing in on those choices much faster.
  • Flying with a specific goal makes soaring even more fun.  Sure, even without a goal it is fun to take advantage of the wind and the sun and enjoy the amazing sight-seeing that can be had high above the Rocky Mountains with all of Colorado spread-out below.  However, I’ve found that on days when staying up is super easy the level of fun increases to another level by adding some additional challenge and being able to measure progress against that challenge.  Try it out!
  • Convergence lines can be the key to flying fast – especially in this area where they are a very frequent phenomenon.  Even if the lift along the convergence is only 1-2 kts it basically means you can fly in a straight line (maybe with slight route deviations here and there) without having to stop to thermal.  You are much faster overall when floating along at 60 kts IAS at 17,000 feet than to push 80 – 90kts between thermals, then stopping to climb before putting the nose down again.
  • Always remember the power of lee side sink.   I made the right call when I decided to transition to the divide from Gross Reservoir via an established convergence line towards Mount Evans.  Flying there directly into the wind would have likely been impossible.  I should have remembered this lesson when I tried it again a bit later over Estes Park.  Although the distance to bridge was much shorter flying in heavy lee-side sink against the wind requires a lot of excess altitude.

6 Replies to “Diamond Goal in 2 Hours 34 min”

  1. How could you complete Diamond Distance on that flight? This has to be done around pre-declared turn points as well as far as I know 😉

    1. Albert – “The FAI Diamond Badge involves 3 required elements. Diamond Altitude is a 5,000-meter (16,404-foot) altitude gain above an in-flight low point; Diamond Goal is a 300-km (186.42-mile) cross country flight using a pre-declared Out and Return or Triangle course; Diamond Distance is a 500-km (310.7-mile) cross country flight.” So my reading is that the 300 km must be pre-declared (which it was) and the 500 km does not require pre-declaration.

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