Tuesday, March 23, 2021

Coming Up For Air: a slice of Waianae leeside

Short version:  We flew the Knob on a weird day.

Long version:  For those who appreciate a no-holds-barred geek-out on my approach to site assessment, read on.

By anyone's standards, January 2021 was a swell time to fly paragliders on Oahu. Nanakuli, Kahuku Motocross, Dillingham, Diamond Head, and the Koko twins (Head and Crater) were in regular rotation in addition to the tradewind staples of Makapu'u and Kahana. End of the World was cranking out the goods for those pilots who appreciate a higher-amplitude experience. Sure there was some rain, but just enough to make you appreciate the sunny days. Covid was in retreat and a hard-charging squad of visitors led by Matty Senior was ticking off head-slapping flights in a style that could only be described as "homing pigeon-esque". Regardless of launch site, they always seemed to land back at their rental in Haleiwa. The crazy flight plans that get tossed around over beers started to sound pretty reasonable. Then, the switch flipped and as February wore on, we adapted to a new diet of shrieking north winds interrupted by fronts dumping more wind and buckets of rain from the southwest. Rinse, not quite dry out, repeat.  

The climax of the punishment came in early March when a week of epic downpours finally finished off the North Shore and windward side. The weather radar showed angry red cores sitting over the upper half of the island for days. Haleiwa was underwater and the Kahana landing zone was erased, leaving the roots of the ironwoods sticking out into space over the surf. The floodwaters had begun to recede by Friday the 12th, and the crew pounced on an uncharacteristically dry southwest day at Diamond Head. Saturday the 13th looked like a marginal tradewind day and I joined the Makapu'u crowd for a brisk northeast jaunt between rain clouds. Later that night I sat down to the business of geeking out over the forecast and to my surprise, found wild divergence between the models. Even though the day in question was less than twelve hours away, the GFS was calling for strong northeast across the whole island while the Euro (ECMWF) model was indicating light north or northwest, or possibly southwest, depending on time of day. ARW was somewhere in the middle. What the hell?

A closer inspection revealed that the crux of the uncertainty was a low pressure trough stretching up just north of Maui. Overnight, it was predicted to pinch off into a tiny spinning low, whirling counterclockwise and drifting west towards our humble little Windlines community. The GFS pegged the rate of drift slow enough that Oahu would be on the west side of the low, smack in the winds blowing north to south. Euro model, pictured below was thinking the swirling eye would head west quicker, so that by mid-day the island would be in the lighter winds at the center of the system, and towards evening might even get north and southwest tickling separate sides of the island.

I went to bed confident this little squabble would be resolved by the morning's update. Sunday morning the 14th was still and sunny over the center of the island, with cumulus already building over the mountains at 0800. The sensors were showing overall light northeast wind but with typical local perturbations created by the reversal from catabatic to anabatic flow. As the models updated, it became clear that they hadn't found common ground. GFS was calling for strong northeast mid day and Euro had the light north/southwest combo still on the menu. Neither of those scenarios correlated with what we could see in the air, or on the sensors, but it was obviously light, so I was considering a Nanakuli mission. From the high ground behind Diamond Head, I could see nice cumulus developing in the west side valleys.  

An hour later I was out the door, and glanced back at the Westside before getting on H-1. Holy Overdevelopment, Batman! Apparently the first strongly sunny day in weeks had lit the fuse, and the ample moisture in the terrain was getting cooked out and sent skyward into an unstable atmosphere unmolested by strong meteo wind.

With Nanakuli now out of the question, I made my bid for the North Shore. The Euro and ARW were matching a little more closely in the morning update, and now the sky and sensors were starting to agree with these two. This left the GFS hopelessly claiming that at this very moment we should be seeing 10-20 mph northeast wind across the island. Sorry buddy, wrong again as usual.

The main glitch in my plan was the fact that the radar was showing a spiral arm of moisture from the spinning low on a collision course with the North Shore. I figured that if the Euro/ARW were correct then the whole low system might keep drifting west and the moisture bands would head out past Ka'ena and give us a break later in the day. By noon, the sun had begun to vaporize the moisture around Dillingham airfield, and clouds of mist hung in the air, pooling in the canyons. The surf was unruly and created its own 'ehukai, combining with the low fog and falling as a light drizzle in the thicker spots.  The windsock near the runway hung limp and a few miles offshore a black wall sat motionless, giving no clue to its intentions. It looked like the day was a bust and I drifted off to a catnap that ended when a slight breeze came through my window from seaward. The offshore block of darkness hadn't come any closer, in fact it had moved west, leaving an opening for sun and cumulus to start spreading outwards from the Waimea Bay area. While I dozed, pilots had reported in from Kahana, Makapu'u and Kahuku motocross and it looked like the Knob might actually be the most promising option in spite of the veil of drizzle mist. 

To be clear, it still didn't look good. There were barely perceptible cycles wafting off a glassy ocean, enough to move individual blades of grass. Above, the higher cloud layers were marching offshore out of the southwest at a steady clip. Ten minutes later I found a parking spot at the Ka'ena point trailhead, shouldered the glider and promptly sunk to my shins in surprisingly cold water that had collected invisibly under the false-bottomed grassy trail. Knob 1, Pilots 0. I've heard about people adapting a "no-fly" rule that states if three things go wrong before you launch, however minor, you take the cue and stay on the ground. It sounds like a great rule when you're nodding soberly listening to other people talk about it, but when you're plodding up to launch on a marginal day with soggy shoes and one strike already, it sucks. 

Standing on the hill I could see the situation had improved in a couple small but important ways. First - the cycles, while very light, were consistently tracking up the gully to the west. There was no question about which side of the launch would give the best opportunity. Second - more pilots were on the way! The Colorado crew of Dusty, Jessar, Alex Young and Johannes were en route as well as our own Alex, a Knob pioneer/funky conditions enthusiast. Assessing leeside is bread and butter to pilots from the Rockies front range, so I spent the next hour waiting for the cavalry while drying socks and cleaning up the worst looking branch snags off the west facing layout spots. Faint texture built on the nearshore water, which was torn up by rip currents and backwash from the hefty sets which capped on the outer reefs before unloading in the shallows. The sensors were showing north to west/northwest flow between Sunset and Mokuleia, while the upper layer well above ridge height was clearly running out of the southwest.  

The main safety concern in this scenario was obviously the potential for leeside turbulence or rotor. There was no evidence of this on launch. All the air was blowing anabatic with the rhythm of normal thermic cycles. The big question mark was what the air column out away from launch was doing, so I was happy to wait for some more eyes to show up to assess the day. By the time the Colorado crew had dropped their packs, the cycles had improved in strength and frequency. For sure we could launch this thing if so desired. Alex elected to hang back and practice his ukulele in the shade of his truck at the LZ, unconvinced there was any flight worth hiking up for. The scene looked a bit like this:

Of the pilots on launch, I was most interested in Dusty's assessment since I've flown with him enough to get to know his style and relationship with risk, which seems to match up pretty closely with my own.  He's been instructing in the Colorado front range, and to do that successfully means you've got to have healthy respect for leeside and its effects on newer pilots (like me). We watched about a dozen thermal cycles blow through, seeing them track from the bushes down low on the slope, then up the gully, then finally rattling the trees just below launch before blowing smooth on our faces from the west for about twenty seconds and back down again. The three pilots new to the site noted how cross it felt, that the apparent wind on the cycles seemed to be hitting us directly sidehill, instead of from the coast. I knew that this was not unusual for this spot: on the more classic days the cycles still come from the side due to the topography of the gullies. The albatrosses and doves had been calmly soaring above us the whole time, but then Johannes spotted a pair of tropic birds circling up into a wispy thermal cloud a couple hundred meters directly overhead, and it was game on.  

Dusty and I went to lay out our gear almost at the same time, and while I set up off to the side to sort out lines, he dropped his blue/green Fusion right across the hilltop, facing west. I was relieved to see that he would be first off the hill and we spent the next few cycles trying to nail down that elusive spot in which the pilot has room to step back just a little, while still getting the wing up into the flow. Eventually he moved down the slope to a grassy ledge with the sail laid out right at the sloping edge, and he pulled up clean into the next cycle, turned, and lifted into a nice parcel of air, rising gently and tracking fairly close to the slope heading west. On his next beat back, he was way over launch and it was clearly working. I set up next on the same low ledge, and it was an odd feeling to have the glider mostly out of view above me.  It caught the flow great in that spot however, and it was easy to inflate the center of the wing, checking the direction of the cycle before committing and going. By the time I made a couple passes, Dusty was high enough to start tickling the edge of the southwest flow and reported finding the turbulence just above 1250 feet.  

Close to the hill, it felt like a buoyant soaring day, the west facing fingers giving great lift, with gentle sink in front of the gullies. Away from the hill, small but sharp thermals were giving 2-3 m/s climbs. When I heard Dusty call out the level of the shear layer, I immediately wanted to go feel it for myself, like a moth to the flame. It wasn't scary at the boundary, just bumpy and mixed with a lot of input needed to keep the wing from surging around too much. I retreated to the lower air, and made my way west climbing steadily in the "ridge lift". After a minute or two, and about a thousand feet up, I went over the falls in a curtain of sinking air. The wing didn't move from overhead, but I was losing airspeed as evidenced by the wind going quiet in my helmet and I had to fight the urge to touch the controls. I've felt similar sensations in SIV after over-checking the wing after frontals - the wing is overhead, but not flying yet. In that situation, it was parachutal and I pushed some bar to get it going again. This felt similar, but I was pretty sure I wasn't stalling since I had been flying full speed only a second earlier and didn't brake or otherwise disrupt the airspeed or angle of attack. After what felt like a few seconds but was probably only a couple, the g's loaded up again and I glanced at my instrument which showed 5.8 m/s sink at the bottom of the hole. In hindsight, our gliders work by gravity pulling us down through the air column. So if the air is sinking with us, it robs us of airspeed. I don't think putting tension on the A's or pushing bar would help in this scenario, since it's not an angle of attack problem. You just have to wait it out. 

Four out of the six pilots chose to fly, with Colorado Alex electing to hike back down and our own Alex committed to his ukulele practice and providing conditions updates to the folks up in the business. As he put it later "Seeing your wings in the air, I knew exactly what the day was like, and my curiosity was satisfied." You're welcome! I spent about fifteen minutes trying to find a chunk of the sky that was mellow, and the only consistently smooth air was low and tight to the hill. On a day like this, I couldn't justify sitting close to the terrain, so I followed Jessar into a smooth landing at my favorite alternate LZ, a wide spot in the low coastal trail just west of the parking lot. It requires a seventy second walk back to the car, but this glaring disadvantage is more than made up for by the lack of vehicles, boulders, or power lines. Dusty and Johannes touched down soon after, and everyone had a huge smile despite the non-classic conditions. At the debrief, Dusty mentioned that although the turbulent bits weren't especially distressing, he found that the air was really nice as long as you "stayed in the barrel". I probed a little bit, but still didn't quite understand what he was talking about so a few days later we sat down again at the Kahana picnic table under a frigid but clear night sky to do another breakdown, this time in interview format.  

When I grill the local gurus on conditions, site assessments, and tactics, I don't always get answers that are immediately applicable to my stage of learning. I'm continually peppering Alex with conditions assessments to see if it matches up with his take on things, and while he is always patient and takes the time to do a breakdown, I get the feeling that in explaining stuff, he has to reverse engineer the logical explanations of something that he already knows from decades of pattern recognition. When I first started flying Makapu'u, I told FireDave that I had been waiting for months until I felt like my high wind launches were pretty solid. His reply? "Oh, strong wind is easier! You just pull the glider up and you're flying!"  Classic. Thanks for the beta! Sitting down with Dusty to pick his brain was nice because he's familiar with the sites, having flown out here on trips since 2014, and as an instructor pretty good at breaking things down into concrete examples I can understand easily.

My main question was: how did he know the air column in front of launch was going to be friendly to gliders? The upper wind was coming over the back, and the seabreeze was pretty cross from the west.  Was this a 99% decision, or was he more confident than that? In his answers it turned out he was using the same pieces of information I was using, but more confident in trusting them, probably because of his much greater experience both at the Knob and all over the world. He knew the upper layer over the back wasn't sending turbulence or sink down the gully as evidenced by the soaring birds, lack of downdrafts, and the mellow predictable cycles of the thermals. Chilling at the LZ, Alex was reporting normal seabreeze from the northwest, with a very reassuring finding of the sea mist from the coast visibly and smoothly blowing up the slope. It was like having a smoke machine map out the flow down below ridge height. Dusty felt that the setup was very similar to other spots he has flown safely including Iquiqe, Chile. Was there any difference in choosing cycles or the actual launch decision compared to a more straightforward day? He told me yes, this was the reason he waited for a long, steady cycle before inflating: he wanted to ensure he stepped into a rising parcel and not the ratty air on the backside of a cycle. Also, he took the time to ensure a bombproof open glider overhead with no tip tucks or other minor issues that a pilot might happily huck off with in a less challenging environment. What about his decision to stick close to the terrain after launch rather than push out in search of thermals? He said he was getting consistent smooth lift tucked in, so felt fine using that lift to get some altitude before turning and searching. What was his take on that layer of turbulence at 1250 feet, and the sinky air away from the hill? That, he replied, was what you would normally expect in a rotor situation, and the key to avoiding the choppy stuff was to "stay in the barrel". The Barrel? Yes, in the Colorado front range, leeside flying is a thing, and he has had success mapping out the rotor using birds and other gliders as indicators, and as long as you stay in the barrel it can be a pretty nice experience. Further probing revealed that what he's calling the inside of the barrel is the rising air close to the terrain created by the "standing wave" of air falling over the ridge and curling back up the inside. So just as a surfer rides the smooth rising wall, staying out of the falling lip, the astute leeside pilot positions himself in the nice part of the wave rather than the crashing sinky bit.

I wanted to know if Front Range pilots really do just huck into wild rotor all the time to learn the finer points of the craft, and to my mild disappointment it turns out they don't, mostly. They have the benefit of thrice-daily balloon soundings, so if the west wind is confined to the upper layer, and for instance at 9000 feet everything is groovy, it's likely going to be mellow. However if the west creeps down to around mountain height, it's a good time to do other activities. For Dusty, that includes flying RC planes which sounds like a fantastic way to gain airtime flying in all manner of turbulence, which would certainly help build up those mental models of airflow in challenging situations.  

As this piece goes to print, we are looking at yet another week of low systems coming through, maybe with some rain, hopefully not so much that we get shut down, again. This winter is not yet over and there is plenty more off-label conditions to be had. When I was just getting started in this game a year ago, I was under the impression that Oahu was the land of straightforward ridge soaring that would probably get boring after a couple weeks, and I would need to go to the "real" sites on the mainland to flesh out my toolbox. It's hilarious, and cringeworthy to even say that out loud! It's been fantastic to get the smackdown over and over again as I try to figure this place out. Thanks as always to all the people who have helped to keep me mostly between the lines so far. See you on launch! - Patrick   

1 comment:

firedave2 said...

Patrick you have become the official cronic chronicler, keep it up.

I remember sitting eating breakfast in Cortina Italy, back like 2002, on a cloudy, rainy day. I asked the waiter where the paragliders fly from? His reply was that "It is a good day for hiking". In hindsight, that was the polite Italian way of saying it is a bad day for flying. But with a good year of flying under my belt and having flown all the epic spots earlier in the trip, places like Chamonix, Lauterbrunen, Canazei; I thought I should at least check out the launch. After a long drive up dirt roads in my friends Alfa, they tossed me out to walk the last mile or so. I arrive at the top of the ski slopes with a couple of grand of vertical Dolomite cliff behind me. Not a human to be seen, like my own world. The clouds above the cliffs above are pumping over the back and dark and menacing, terrifying sort of.

I sit down to motivate myself for the long downhill walk back to Cortina, but I notice a very light wind flow coming up the ski slope. Somehow I decide that I will just fly down the ski slope to shorten my walk a bit. I have that old back and forth pep talk to tell myself this isn't a bad idea. After an easy forward launch, I fly away from my grassy slope and the mountain and am now 1000' over the ground. I abandon the ski slope landing and head out to the main LZ, which is out of sight behind a small ( for this place) mountain a few miles away.. I skip any lift I bumble into, as I have no interest in getting higher.
Eventually I round the rocky hill and spot a landing zone a 737 could land in. I land in light winds, in a deserted world and phone for a ride home.

Was it a bad idea to fly, probably. Was it an adventure in self-doubt certainly. Did it work out fine, fortunately. Would I do it today, unlikely. But the great thing is that this sport makes all types of fun available to you.