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.  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.

First 500km Flight, Pikes Peak Bagged

This past Thursday was likely going to be the best soaring day of the week.  Still, I wasn’t sure whether it would be a great day or merely a good day.

SkySight predicted a strong thermal flying day with attainable flight distances from Boulder between 500-600k for 18m ships (which have a somewhat better performance than our club’s Standard Class 15m Discus). Note that going east from Boulder into the dark red colored area is not practical since most of that area is part of restricted Denver Class B airspace.
Topmeteo was a lot more bullish and predecited outstanding soaring conditions for almost all of Colorado with potential flight distances of up to 1000 km.

Thermal height was going to increase throughout the day to approx. 20,000 feet MSL over the mountains with the highest cloud bases to the southwest.  Thermals were projected to be strong with climb rates of up to 10kts or even more.  There were going to be winds of 10-20kts aloft, mostly from the southwest.  These winds could complicate thermal flying:  increasing winds with altitude tend to distort thermals breaking off from the ground and the strongest lift is often limited to upper-level convection, i.e. close to cloud-base.  In addition, it is important to be careful on the lee side of taller mountains where such winds tend to cause significant sink and rotor turbulence. There was a good chance for cumulus clouds and a low risk for overdevelopment.

From the soundings it looked like the day might start as early as 10AM over the foothills and significantly later in Boulder – a common scenario due to the morning inversion down in the valley.

As I did the pre-flight checks on the Discus there was a slight easterly breeze on the ground – also a very common phenomenon – and an indication that there was likely a convergence line somewhere over the foothills where the easterly wind from the plains meets the westerly airflow aloft.

SkySight illustrates the convergence line running along the foothills (shown in dark red): this is where the eastern airmass from the plains meets the dryer western air mass spilling over the Continental Divide. Note that this forecast is for 1:30 PM MDT. The position of the convergence line tends to shift throughout the day – often it moves further west as the day progresses. I speculated about the reasons for this in my previous post.

Whenever conditions conform to this fairly typical pattern I have learned that it is important to get to the west side of the convergence line as quickly as possible:  thermals on the east side tend to be fairly weak and often top out at less than 1000 feet AGL – especially in the morning when they are trapped by the inversion layer.  Unfortunately this often means a long (and expensive) tow over the foothills is necessary to connect with the lift on the west side of the convergence.  (Note that usually you don’t have to tow all the way back to the convergence but you have to tow high enough to be able to glide west until you’re able to connect with rising air on the west side.  If you don’t steer decisively west and linger on the east side you might quickly find yourself too low to get far enough west.  This is especially true early in the day when the thermals on the east side are still non-existent or extremely weak. )

When I launched at 10:42AM MDT the air above Boulder was still as calm as it could possibly be – a sign that the inversion still suppressed any thermal activity over the plains. The first time the air started to stir just a little was after the towplane had turned west over the foothills (west of Altona).  However, the climb rate on tow remained constant until we had climbed to 10,800 feet over Jamestown and I decided that I was now high enough to push further west on my own as we still had not reached a thermal.

Flight path on tow shown in dark gray. Flight path off tow shown in light blue. Release point over Jamestown. My first attempt to climb off tow was on the east side of the convergence line. Lift was weak and uneven. A few miles further west everything changed and climbing from 10,000 to 16,000 feet was almost effortless.

I headed straight toward a cloud a few miles further west.  East of Hidden Lake I reached the east side of the cloud and found some weak lift.  I tried to climb in it but the air was rough and the lift weak and inconsistent.  The wind drift was from the SE towards the NW.  These were all indicators that I had reached the convergence line but that I was still on the east side.  After several turns (probably too many) I decided to push to the western edge of the cloud.  And voila, just as I had hoped, I had reached the west side of the convergence line and within 10 minutes I climbed from 10,000 feet to just under 16,000 feet.

As I started to head south I could easily see the position of the convergence line by looking at the curtain clouds underneath the next cloud in front of me.

The curtain clouds in this picture are a perfect indicator for the position of the convergence line. Good climbs can be found on the west (dry) side.  The nice clouds further south (on the right hand side of the picture) suggest a quick and easy flight route ahead.  My position in this picture is a few miles north of Ward above the Peak-to-Peak Highway, looking SSE.  The city of Boulder is on the left edge of the picture.

Two quick climbs above Nederland and south of Idaho Springs took me up to 17,000 feet – high enough to push through the potential sink on the lee side of Mount Evans.  The air above Evans was rough but I found two reasonable climbs southwest of Mount Bierstadt that gave me the altitude needed to fly further southwest into Southpark where I saw some promising clouds north of Como.  At this point my goal was Buena Vista and – if all went well – perhaps Salida.

I climbed in ok-ish lift near Fairplay and headed for some nice looking clouds near Antero Junction.  However, none of the clouds along the western rim of South Park worked well at all.  I could not make out a good reason for this but when the fourth or fifth cloud provided only mediocre lift I decided to change course and save Salida as a goal for another day.  A few miles to the north I saw several nice clouds right through the middle of South Park, spread about 10 miles apart.

These worked and within 20 minutes or so I had reached the east rim of South Park.  This area worked particularly well: it was now early afternoon and the combination of wind and sunshine from SSW provided for great lift above the SW facing slopes on the east side of South Park.

At this point I had my eye on Pikes Peak. There was a blue hole right around the mountain but it was not nearly as big as during my prior attempt.

Pikes Peak approx. 10 miles away and – somewhat surprisingly – free of any clouds. At the point of this picture I was above 17,500 feet and the summit at 14,114 feet seemed within easy reach. However, it wasn’t going to be that easy.

The wind was blowing at 18 kts from SSW so I decided not to fly straight toward the mountain but instead to pass it on the west side and then approach it from the SW.  If I wouldn’t find any lift along the slope, I would have an escape route to the south towards Fremont County Airport near Cañon City, which I figured was easily reachable even flying against the wind.  There were also some nice looking thermals in that direction giving me extra confidence.

As I approached Pikes Peak the air turned very rough with strong sink.  A few miles SW of the summit I reached a low point of around 14,500 feet – just a few hundred feet higher than the mountain itself – too low for comfort to fly over the peak.  Fortunately I found a turbulent thermal breaking off from the ridge line below me.  Although it was extremely disorganized and caused erratic movements of my vario from +10kts to -10 kts I was able to climb to 16,700 feet – high enough not only to fly over the summit but also to reach the next cloud, which was approx. 10-15 miles further north.

I was surprised to find strong sink on my approach to Pikes Peak. The climb above the ridge SW of the summit was quite rough.  Also note the sudden (and non-obvious) change in wind drift from SW to WNW after I crossed the little lake below the summit.  The air near big mountains can be very fickle.

Having “bagged” Pikes Peak, I decided to head back towards Boulder while remaining on the lookout for worthwhile excursions.

View of Pikes Peak from the West just as I was getting into strong unexpected sink during the approach. The climb that took me back up over the top was just above the ridge line near the little lake on the right edge of this picture.

The clouds in front of me looked solid.  However, when I got to the nearest one, north of Woodland Park, the climb rate was disappointing.  I wondered if I was too far east – perhaps the air from the prairie had penetrated over the foothills, suppressing thermal activity?

I decided to turn west again towards the east rim of South Park where I had experienced much stronger climb rates some 40 minutes ago.  However, my next three thermals were equally poor and each time I decided to push on without gaining much altitude.  Lee-side sink north of Buffalo Peak caused me to loose another 1,500 feet.  I was now below 13,000 and worried that I might lose my connection to the clouds.

Just as my mind was working on fall-back options: Perry Park airfield was still within reach (though barely) and an off-landing field near Roxborough Park (which I recently checked out on the ground) was more easily accessible, I found a modest climb southeast of Bailey.  When you’re down to 12,700 feet over unforgiving terrain and with another 50 miles to go to Boulder you can’t be picky.  I carefully centered the thermal and happily spent the next 12 minutes climbing back up to 17,500 feet.

A succession of frustratingly weak climbs led me to a low point of 12,700 feet SE of Bailey. Perry Park Airfield was 30 miles away (requiring a 35:1 glide ratio). The nearest comfortable out-landing field was just over 20 miles away, NE of Roxborough Park.

It only takes one climb for the world to look totally different again. I steered to the SW side of Mount Logan (just SE of Mt Evans), climbed again to just under 18,000 and decided to fly north.  Maybe I would find lift above the Continental Divide so I could extend the flight to the north towards the Wyoming Border?

However, when I got to the Divide near Mt. Eva the route to the north along the Divide did not look promising.  Rain showers and virga obscured the sight and the area appeared over-developed.  To my left however, there was a nice-looking cloud street towards the SW.  I followed this line until Berthoud Falls when the route ahead also seemed be over-developing.

I made a 180 degree turn.  Looking north from my new vantage point I could suddenly see what was going on:  the convergence line that had sat over the foothills in the morning had crossed over the Continental Divide.  What had looked like rain showers and virga when viewed from the East side were in fact curtain clouds marking the position of the convergence line.  Further to the west the sky was completely blue.

Beautiful view of the convergence line on the west side of the Continental Divide. I took this picture after my northern turn-around point. The curtain clouds marking the convergence are clearly visible.

I decided to follow this line to the north, always staying to the west of the curtain clouds. It worked amazingly well.  I followed the line of curtain clouds that paralleled the divide.  Flying between 80 and 100 kts IAS I was able to maintain my altitude of around 17,500 feet over a distance of 38 miles in just 16 minutes.

The power of a convergence line: 38 miles in 16 minutes, that’s an average ground speed of 142 mph. Without losing altitude.

North of Longs Peak the line became less clearly defined and the cloud base dropped so I decided to turn around.  I followed the line south past Apache Peak and then decided to return towards Boulder.

Grand Lake and Lake Granby viewed from the west side of the Continental Divide near Longs Peak.

My final glide took me past Gross Reservoir towards Golden where I checked out the model plane airfield near Arvada from the air.  I recently visited this field on the ground and determined for myself that its perfectly paved 700 foot runway is a viable out-landing option (land on the N side of the runway to minimize the risk of hitting a fence and watch out for the power lines on final).

From there I followed the ridge line of the Flatirons on my way back to Boulder.  The winds at Boulder airport were 3 kts from the NE.  I briefly considered landing on G26 but ultimately opted for Runway G8.  I’m glad I did: as soon as I climbed out of the cockpit to get the dolly a freakish 27mph gust hit the airfield straight from the east. The gust lasted for about 2-3 minutes, then total calmness returned.  I have absolutely no explanation for this gust.  I just know that landing with a 27 mph tailwind would have been quite troublesome.

It was an interesting end to a challenging and rewarding first 500km flight. The full flight track is here.

Lessons Learned:

  • If there is a convergence over the foothills get to the west side before you are too low. This is especially true in mornings with strong ground inversions when there are still no viable thermals on the east side.
  • Always have a viable landing field in mind.  I caught myself a bit by surprise when I was down at 12,700 feet and noticed that getting to Perry Park would have been doable but already a bit of a stretch.
  • Approach big mountains with respect.  They can make their own weather and it’s not always what you might expect.  E.g., Pikes Peak surprised me with sink on the west side, which had direct sun exposure and was facing the wind. (It reminded me of a video from Bruno Vassel confidently approaching the Tetons from the west only to find unexpected sink.)
  • Keep in touch with the clouds when you can.  Throughout the flight I noticed that the climb rates improved the closer I got to the clouds.  This phenomenon seems to get more pronounced throughout the day.  Thermals down low were quite poor and wind-blown.  But close to the clouds the upper-level convection was quite strong, often with climb rates of close to 10kts or even more.  Staying high isn’t only safer, it might actually also make you faster (even though you have to center more climbs.)
  • Never get caught in lee-side sink.  I should have been more mindful of the terrain when I was flying just below 14,000 feet N of Buffalo Peak.  I turned northeast in direct pursuit of the next cloud and got into sink on the back side of Windy Peak. This could have been easily avoided had I followed the ridge line before turning towards the cloud. (It probably would have saved about 1,000 feet, which could make all the difference when it comes to reaching a land-out field.)
  • When it comes to wind, always expect the unexpected, especially in the pattern.  The freakish gust after landing was completely and literally out of the blue. (I had monitored the conditions in Boulder on the radio off and on for the past 20 minutes and conditions had always been calm.)