World Record Weather
By Davis Straub, with lots of help from Gary Osoba and James Keller
You
need a weatherman to know which way the wind blows.
If you are want to set the hang gliding world record for distance (the only one that any one remembers), you've got to go a site that has world record weather. Hey, doesn't that just seem so damn obvious? Well, if it was so obvious, why have pilots been going to the wrong places all these years?
It's not easy to figure out where to go unless you're already there (and you've seen and felt the weather). The weather patterns that make for world records are difficult to ferret out (amongst all the abstractions about weather you haven't experienced directly). Until recently the kinds of weather analysis tools that are needed for the job haven't been generally available. High quality weather sites on the world wide web have changed all that.
For the most part pilots keep going back to the places where other pilots have previously set world records. This is the easy way out, because it doesn't require a lot of meteorological knowledge or study on the pilot's part. It has one big problem, what if the site's potential has already been maxed out by the previous world record? Pretty likely, wouldn't you say?
Pilots looking for world record distance flights in the US keep going back to Rock Springs, Wyoming and Hobbs, New Mexico, because these are the places where Larry Tudor went over 300 miles. Larry was the only hang glider pilot to do so before the new Millennium.
So you think that you are a better pilot than Larry Tudor? That Larry didn't take advantage of the best conditions on the best days when he was in Wyoming or New Mexico? You really feel that you can do better there?
I sure didn't think that I could beat Larry's records, even though I felt I had the advantage of a better glider when I first went to Hobbs, New Mexico in June of 1999. At that point my longest flight was 142 miles. Michael Champlin had talked me into going to Hobbs assuring me that in spite of the stories that I had heard that I would enjoy the air there.
It turned out that he was right that the air over the New Mexico and Texas flatlands was pilot friendly, but the stories were right also. Hobbs has a big problem with the weather associated with the "dry line." You can get near or under the dry line and fly fast, but you can also be shut down really quickly when it over develops.
Michael spent years trying to outdo Larry. Despite the fact that he probably had more flights over 200 miles than any other hang glider pilot, he was never able to break 300 miles. So you think you can do better? Pretty unlikely at Hobbs or Wyoming, where Michael also attempted to beat Larry's record.
Gary Osoba is a Wichita sailplane pilot. He's also a former hang glider pilot and hang glider manufacturer (the Pliable Moose). In addition, he's an engineer, aero dynamist and an entrepreneur. On the side, he is a self-taught meteorologist. Self-taught, like the rest of us hang glider pilots, but he's taken it a few steps further.
Gary's had the opportunity over the years to fly one of his sailplanes in Texas. Sailplane and hang glider pilots have known for years that there is some pretty good cross-country flying in Texas. There were national and regional sailplane contests out of Marfa, Texas, south of Hobbs, NM. Those pilots flew in the general air mass associated with Hobbs.
Also there were national sailplane contests at Ulvalde, west of San Antonio. On and off hang glider pilots flew in this area also. Geoff Lyons had set the Texas state record of 273 miles flying from Big Springs in central Texas into Kansas.
Texas hang glider pilots were limited by the lack of mountain launches. Platform towing was used extensively, but was limited to areas near existing hang glider pilot populations. Until two years ago there was no aerotowing in Texas. All these limitations led to a general lack of knowledge about the cross-country potential available in Texas amongst the national hang glider population. Again, no one had enough personal experience with the weather patterns in all the parts of Texas to be able to know from their experience how really good it could be. After all, Texas is a pretty big place.
Gary started studying Texas weather patterns a few years ago looking for a specific pattern that could provide the conditions for a long straight-line distance flight. He wanted to fly his Carbon Dragon at least 450 miles to set a new world record. In 1999, he flew at Uvalde to get a feel for what the weather data was telling him about south Texas. It looked good.
There don't appear to be any hang glider or sailplane pilots living in south Texas. Lots of folks only live there during the winter, as it gets very hot in the summer, the best time for flying cross-country. Without local pilots there are no stories circulating in the sailplane and hang glider communities about the great flying in south Texas even if the potential was there.
With no pilots living in south Texas, we had nothing to go on other than Gary's limited experience 150 to 200 miles to the north, and his analysis of the general summer weather patterns.
Going
down wind
So just what kind of weather do you need to go long distance in a hang glider?
As Gary told us when we visited him in the summer of 1999 in Yoder, Kansas, the first criterion is wind. If you don't have a tail wind, you just won't go that far in a hang glider.
Over a triangular course (which averages out the wind component) a top hang glider pilot will be able to average about 25 to 28 mph over the ground on a day with strong, consistent lift. You can fly at about 40 mph between thermals, but you spend a lot of time going no where thermaling at 25 mph in circles.
Take a look at the record of air speeds over a two-hour period for a flight I had when I set the world record for ground speed over a 100-km triangular course (average 22 mph). The trace shows that I'm flying at essentially two speeds. One speed during thermaling of about 27 mph, and one speed during gliding of about 37 mph. The next day I was able to average 28 mph over a 100-km triangle.
If you want to travel at least 300 mph during a flight that you hope lasts at least ten hours, then you are going to need a tail wind of at least 5 mph if not 10 mph. The 28-mph average that I did around a triangle came during the best two hours of the day, and you aren't necessarily going to be able to average 28-mph air speed for ten hours. You might have to perform a low save now and then during your flight.
If you can find a site that provides 20 to 40 mph tail winds for most of the day all along the line of your flight, then you can going to have a much better chance of going far than if you're at a site where the winds average 5 to 10 mph.. Given the slow average air speed of a hang glider, a strong tail wind is a large component of the glider's ground speed. If the wind speed is 25 mph, it makes up about 50% of the glider's ground speed, and you can average 50 mph. Stay in the air ten hours, and you've gone 500 miles.
Given that Larry Tudor averaged 30 mph during his record flight and I averaged 35 mph during mine, you can imagine that we haven't yet tapped the full potential for using a strong tail wind to go really far. Of course, it isn't quite that simple, but a tail wind is the major component of a long distance flight.
If you are going to go far in one direction, you'll want the tail wind to stay with you in a straight line through out the whole flight. Winds are almost always circulating around a high or low pressure, although it is sometimes possible to move along with a front that travels in one direction during the day.
Given that in general the winds are circulating it is difficult to find a wind that goes in a straight line, unless the circulation pattern is so big, that the winds far removed from the center of the high or low pressure go in essentially a straight line. Since hang gliders go so slow it is hard for them to go really far over a day. If you find a wind pattern that provides wind lines that are pretty much straight over 500 miles, then you've basically got a consistent tail wind that takes you in one direction.
If you are out west in the US there are lots of topological features that will disturb a wind pattern that would otherwise last for 500 miles or more. Basically all long distance flights take place over flat lands because they won't change the wind's direction.
Flat lands also have the advantage of reducing the amount of localized turbulence, rotors and shears that the pilot would experience flying at higher wind speeds. Mountain tops and ridges cause severe mechanical turbulence in high winds limiting the pilot's options as well as making the flight much less pleasant.
Thermals that develop over flat lands have a much better chance of remaining coherent in strong winds than thermals generated over mountainous areas. The stronger and more coherent the thermals, the faster we are able to climb.
You want a wind that will last all day and remain strong throughout the flight. If you move toward the center of low or high-pressure, the wind speeds are reduced. You want to fly along a line tangent to the general circulation pattern of the winds. The pattern has to be large enough so that the winds you encounter in the morning are the same winds that you encounter 300 plus miles away from your launch site late in the afternoon.
Gary saw that a large meteorological feature developed in the Gulf of Mexico in the summer – the Bermuda high. This high-pressure region was so big that it dominated the weather from east of Florida to west Texas. From the Yucatan to Oklahoma City.
The center of the high pressure, when it was situated just right would be south of New Orleans, Louisiana, and east of Brownsville, Texas. The winds associated with the high pressure would circulate clockwise, bringing south to southeast winds to south Texas.
The high pressure wasn't a once every couple of days things, but a consistent pattern. Day after day the high would remain out over the Gulf of Mexico and the winds would consistently rotate clockwise around it. Weather disturbances coming from the west and north would bounce off it and go through Kansas or the Dakotas.
This consistency is important because it dramatically increases your chances of setting a world record. There are many factors that effect your ability to set the record, so you like to have your main aid to record settings consistently there.
Consistent wind direction is the result of a consistent weather pattern. Consistent wind direction makes for easier route planning and retrieval. It allows you to launch from one spot and not have to chase the winds.
Gary studied the wind patterns by looking at the national charts for 850 millibars (or 5000' MSL in a standard atmosphere). These charts (http://weather.unisys.com/ruc/ruc_850_init.html and http://weather.unisys.com/ruc/) show the wind speed and direction (in addition to temperature at 850mb and height of the 850-pressure region). Here's an example of a chart from late September, long after the high pressure in the Gulf has dissipated.
By looking at the white arrows you can see the direction of the wind and its speed at 5000'. When the high pressure sets up in the Gulf, the arrows line up from south to north right through Texas. In south Texas they'll have an eastern component as the winds circulate around the south side of the high pressure to the east of Texas.
While Gary was checking out the winds at 5000' MSL, I was checking out the windcasts (http://www.intellicast.com/LocalWeather/World/UnitedStates/SouthCentral/Texas/SanAntonio/WINDcast/d1_18/) for the surface winds in Texas. The winds can rotate and thereby change direction with increases in altitude, so the surface winds aren't the whole story, but they do give you a general idea. We sometimes found that the winds aloft were a bit more southerly than those predicted for the surface. Here is the windcast for 1 PM on August 9th, the day I set the world record:
Prior to deciding to go to Zapata, Gary looked at the wind patterns at a site near Brownsville and at Zapata. The question was: should we go closer to the Gulf of Mexico and head north along highway 77, or start further inland and head north along highway 83. Gary compared the forecasted surface and winds aloft during the day, as shown in the following graph, for a typical June day:
The height in the vertical red and blue bars represent different between the surface winds and winds aloft. Brownsville is the red bar and Zapata is the blue bar. During the middle of the day, the winds aloft inland are stronger than the winds near Brownsville. The winds aloft are quite a bit strong than the winds on the surface, especially during the middle of the day.
This chart shows quite strong winds, combined with lighter winds in the morning and near the surface which would make it easier to launch early in the day without having to be worried about being overpowered while ground handling your glider. The stronger winds aloft would provide that world record push.
These wind readings are for south Texas, and, of course, as the day goes on, you fly out of south Texas and head north. The wind forecasts above show that these winds continue throughout the length of the flight.
To obtain this wind data Gary used the non interactive version of the Rapid Update Cycle model. You'll find the predictions of this model at http://maps.fsl.noaa.gov. Click the Non-interactive menu item, then enter the longitude and latitude for the site you wish to view. Your browser will display a skewed plot of the temperature and dew point with altitude, as well wind speed and direction. It also print out a chart of the data used to create the plot.
The nice thing about this RUC-2 is that it has a 40-kilometer resolution. You can type in your site co-ordinates and you'll get a chart that comes reasonably close to describing conditions at your location. You don't have to be near a reporting airport, as these are satellite-generated soundings.
The chart that follows shows the forecast that can be found at the RUC site. Notice that the wind on the surface (462') is 14 knots at 333 degrees (northwest). It rotates around to 5 degrees at 19 knots at 5111'.
Pressure_Alt DD Dir Spd ---Temp--- DewPt
(ft) (mb) (kts) (F) (C) (C)
462 1003.0 A 333 14 75.0 23.9 6.1 534 1001.0 A 334 15 73.4 23.0 5.9 574 1000.0 A 335 15 73.2 22.9 5.9 679 996.0 A 337 16 72.7 22.6 5.8 895 988.0 A 338 17 71.4 21.9 5.7 1184 978.0 A 339 18 70.0 21.1 5.5 1627 963.0 A 340 17 68.2 20.1 5.9 2070 948.0 A 342 18 65.8 18.8 5.6 2522 933.0 A 342 18 63.5 17.5 5.3 2775 925.0 A 343 18 62.2 16.8 5.1 2979 918.0 A 343 18 61.2 16.2 5.0 3438 903.0 A 346 19 59.0 15.0 4.8 3907 888.0 A 350 19 56.3 13.5 4.4 4379 873.0 A 355 19 54.0 12.2 3.9 4858 857.0 A 5 20 52.0 11.1 2.7 5111 850.0 A 5 19 52.0 11.1 3.3
James Keller points
out, "The RUC forecast soundings come from a numerical weather prediction
model, not from satellites. If you want a near real-time satellite
sounding, go to
http://orbit-net.nesdis.noaa.gov/goes/soundings/skewt/html/skewtatl.html.
The RUC is good for same-day forecasting, from model initialization out
through 12 hours, however to get a glimpse of what weather is coming tomorrow,
the 40 km MAPS output is useful because its sounding forecasts go out through
36 hours. The MAPS sounding data are available at the same URL where
you'll find the RUC."
.
Need
a lift?
While you are going to need a tail wind to go a world record distance, you'll also need to have some lift. Previously pilots who attempted world records thought that they needed wicked strong lift (as well as strong winds). What they really needed was consistent lift and winds that went pretty much straight for as long as possible.
Unfortunately, they went to places with strong lift, and the accompanying strong sink, and with winds that only went so far. They thought that strong lift was the most important factor not realizing that they had to consider long lasting strong winds first and lift second. Given the strong sink that accompanies strong lift, they often sank out.
Consistent moderate lift all along a long route significantly increases one's chance of staying up throughout the flight. If the lift is organized so that the pilot can stay in the general areas of lift even the better. If the lift is visible, as in cumulus clouds, then one's chances of staying up and going faster increase just that much more.
What the pilot is looking for are cloud streets, organized and consistent lift that is concentrated along the pilot's down wind course. This allows for both lift to keep the pilot up, and organization that reduces the time required for climbing. If you can just stay under a cloud street throughout the flight, then you are not going to waste any time circling.
Cloud streets can form when the winds are not changing direction or rotating as you go from the surface to cloud base. Winds are needed to line up the convective cells into streets. The winds therefore help you both by providing a tail wind component and by organizing the lift so that you can maintain a down wind heading and reduce your circling.
One way to generate lift is to bring in a cooler and moister air mass over a warm surface. Say, moist cool air from the Gulf of Mexico over a hot Texas desert.
It is this relatively cool air that forms the "overrun" in Zapata. One day in July this summer the cumulus clouds started forming before sunrise as the wind from the southeast pushed the cool air over the ground that was still warm from the previous day.
The day after I flew 347 miles past San Angelo, we noticed streets forming at 10 AM just south of San Angelo, 300 miles from Zapata, and even further from the Gulf.
Consistent lift that is easy to find and always within reach is much better than strong lift from widely separated cores. Moist air adds the benefit of virtual lift, as the moist air is less dense. If there is drier air above the moist layer, it gets the extra boost just due to the differences in density due to moisture differences.
Thermals don't necessarily start from the ground. If you have a layer of warm air above the ground this layer of warm air can be the source of the thermals. The nice thing about having such a layer of warm air is that when you have it the thermals become more evenly spaced, and more frequent relative to thermals coming straight off the ground.
The layer of warm air is smooth relative to the ground surface thereby encouraging the formation of convective cells that can be lined up into cloud streets if the wind conditions are supportive. Of course, it is much more likely to find such a layer of warm air over relatively flat ground.
You can check to see whether you can expect such a warm layer of air by looking again at the Unisys weather site (http://weather.unisys.com/ruc/). You'll find the temperatures at 5,000 feet at http://weather.unisys.com/ruc/ruc_850_init.html and the ground temperatures at http://weather.unisys.com/ruc/ruc_1000_init.html.
This element of a pilot friendly layer of warm air is a crucial element in increasing the pilot's chances of staying in the air especially when conditions are weak, for example, early in the morning.
The flatlands of south Texas form a huge essentially flat convective surface. The winds coming off the Gulf organize the convection on that surface. Even the hills that rise to 2,400', 170 miles to the north of Zapata, do not disturb the general flow of the convection and winds.
Gary states that, as the delta of the Rio Grande gradually rises to the north and west, the winds coming in from the Gulf are also mechanically pushed up. By the time one reaches the hill country by Uvalde, it is only a 700' jump over ten miles to the Edwards plateau at 2,400'. This gentle rise positively effects the lift during the flight turning a small part of the wind into a vertical component.
Jim states, "The slope of the rising terrain is so gentle that any contribution of the horizontal wind into useable vertical motion would be essentially negligible. If the upslope lift was significant, then the Uvalde area would be under a perpetual convective cloud cover whenever SE winds prevailed, as warm, moist air from the Gulf of Mexico continuously condensed. It is deep layered, downward vertical motion on the order of 1.5 - 2.5 cm/sec that drives 'flying friendly' lift which is generally why flying under the influence of HIGH pressure is superior to flying under the influence of LOW pressure."
Getting
an early start
The more hours that you can spend in the air, the further you can go. The earlier you can start, the more hours you can spend in the air. Gary believes that it is possible to start soaring at around 8 AM in Zapata. This means that a pilot could have 12 to perhaps 13 hours within which to set a record.
Conditions are going to be weaker in the early morning, but if it is possible to start flying at 8 AM, then whatever distance you get is better than staying at the airport waiting for better conditions. What makes this possible is the early organization of the lift by the wind. With cloud streets forming before 9 AM, it is clear that the lift is organized. Lift that is weak due to early morning low solar radiation is much more useful if it is organized.
Cloud bases are low in the morning, but with cloud streets it is possible to stay in the lift until the day gets stronger. Gary looked at the cloud bases by time of day for a site near Brownsville and near Zapata when he was first trying to determine where to go. This chart shows higher cloud bases early in the day near Brownsville, but higher cloud bases further inland in the middle of the day.
It is a rare site that allows pilots to fly before 10 AM and possibly at 8 AM. I was able to launch at 10:15 AM on my record day and circle up right around a cloud street to 2,200'. While this was not particularly high, the streets were so well organized that I had plenty of confidence that I could stay up in them for the next few hours. It was even easy to jump cloud streets, as I had to do in order to avoid the Laredo controlled airspace.
So
how did it work out?
I spent about three weeks trying to set the world record in Zapata, Texas. Everyday the wind blew out of the southeast. I was able to fly mostly north on one day, but more to the northwest on all other days. Flights of 200 miles or more were possible almost everyday I was there.
On most days I was not able to stay up in lift above our launch area, the Zapata County Airport, before 11 AM, but I slept in on a few days in which I could have tried a lot earlier. I never made it out to the airport in time to try a launch at around 8 AM.
Cloud streets formed before dawn on one day, and before 10 AM on maybe five days. On the day I went for the record, the cloud streets started forming at 8 AM. I believe that if I had been ready I would have been able to start at least by 9 AM on that day. Instead I started at 10:15 AM and had good consistent moderate lift for the first hour.
The winds were more easterly than Gary had seen while looking at the data in the third week of June. The cloud streets didn't form as well as we had hoped, but the day after I flew 347 miles, Gary noted a cloud street on the satellite photos that was 170 miles long (also with a more westerly flow).
I was able to fly under fully formed cloud streets for 40 miles in the early morning on the day I went long, and under high cloud streets much later in the day, that were stronger but not as well formed. During the middle part of the flight, I had plenty of cumulus clouds, but they were not as well organized by the winds, and I had to often jump to the east.
With little familiarity for roads that went to the northwest, I stuck as close as I could to a north, northwest road. This meant that I had to fly a bit of a cross wind task, still with a tail wind of about 10 mph.
The winds were not especially strong throughout my flight, about 10-15 mph. Stronger winds would have been helpful as long as they didn't blow apart any of the lift.
We believe that much longer flights are possible at Zapata and south Texas. At the moment it looks like south Texas is the premier location in the world to set long distance world records.