Assessing Flying Conditions

      Mt. Diablo, elevation 3,849 ft., is the highest mountain in the Bay Area.  The park includes thousands of acres of high terrain surrounding the peak.  This geography creates a lot of its own weather in addition to both the marine air influence from the nearby sea and the large scale weather pattern in effect.  When the three weather sources (local, marine, and large-scale) combine it can be confusing and difficult to assess the flying conditions.  Moreover, one weather phenomenon may be dominant at lower altitudes and another at higher altitudes.  A good practice is to observe the weather conditions (winds and temps mainly) during the whole drive up the mountain, including above launch elevation if in doubt.  Particularly, note conditions at the Northgate Road park entrance (elev. 350 ft.), main LZ (elev. 1,000 ft.), alternate LZ (elev. 1,750 ft.), Junction sign-in box (elev. 2,150 ft.), main launch (elev. 2,900 ft.), and appropriate pull-outs along the road above that if there’s any question about the upper level winds.  Only the alternate LZ stop is additional, the others you would generally need to stop at anyway.  Each stop allows you to feel ground-level winds, see foliage and cloud movement from the wind, and see how the “locals” (hawks and vultures) are faring in the nearby air.  And once at launch, it is usually a good idea to eyeball conditions there for at least 10-15 minutes before you commit to flight.

      The wind talker, ph. # (925) 838-9225, is located at the top of the mountain, some 900 ft. above launch, so it can give only an approximation of winds at launch.  Generally, the wind at the peak is a few mph faster and more north than the wind at launch.  However, if the peak is in cloud and launch is below cloud base, the wind speed and direction can be quite different in these two locations.  Another common exception occurs mainly on interfrontal/higher pressure days, when winds at the top can register strong and northerly on the wind talker during the night and into mid-morning, then with solar heating during mid-day the registered winds subside to single-digit levels and become more westerly.  Sometimes this low wind reading is real and represents the prevailing wind, allowing mid-day flying.  But often there is an actual stronger lee-side base wind, apparent only after you’re at the mountain or even in the air, which tells us that the peak (where the wind talker is located) is in a local “thermal calm” while the true prevailing wind (N to E usually) is blowing all around it.  This is another reason not always to trust the wind talker to give the true general prevailing winds.  In fact, you cannot necessarily trust the wind you’re feeling at launch to represent the general prevailing wind; on a strong lee-side day, it can feel almost calm at launch, even with some light cycles coming up.  But a glance at nearby foliage reveals much higher local winds, over-the-back, while launch itself is in a wind shadow or near the center of a rotor where it is calmer.

      An important resource is the Concord Airport ATIS (Automatic Terminal Information Service), 11 mi. NW at near sea level, ph. # (925) 685-4567.  This is recorded weather information for the airport that is updated at approximately 50 min. past the hour.  Of importance to us, it gives cloud cover, visibility, temperature in Celsius, barometric pressure (as an altimeter setting), and winds.  Convert Celsius to Fahrenheit mentally in 3 easy steps: 1.) double the Celsius, 2.) subtract 10%, 3.) add 32.  Example: 16 degrees C. would double to 32, subtract 3.2 (10%) = 29 approx., add 32 = 61 degrees F.  For our purposes, a general rule is that if the difference between the airport temp and the wind talker temp is 10-16 degrees F. we can expect good soaring, depending on winds, ground moisture, cloud cover, time of day, season, and the presence of inversion(s).  A 6-10 degree difference gives marginal soaring.  Over 16 degrees can mean too much convection and associated turbulence. 

      There are web sites for Mt. Diablo and nearby locations that give wind/weather info to help paint the “big picture” for you.  The Mt. Diablo site itself is:  http://cdec.water.ca.gov/cgi-progs/queryFx?MTDhttp://cdec2.water.ca.gov/cgi-progs/queryFx?s=MLR.  A third is Las Trampas, 8 mi. WSW, elev. 1,760 ft., http://cdec2.water.ca.gov/cgi-progs/queryFx?s=ltr.  All three of these and some other Bay Area locations can also be viewed at once as current readings only; just move the cursor over the ones you need and a table with all the current info appears for each one: http://www.wrh.noaa.gov/mesowest/mwmap.php?map=mtr&limit=1.  A good soaring forecast site for Mt. Diablo is: http://home.san.rr.com/tadhurst/Mt_Diablo.htm.  Of course, there are countless web sites for assessing general weather and soaring potential for specific areas, but they won’t be covered here.  You will eventually find and use those which fulfill your needs best.  and it shows winds, temps and solar heating over the preceding several hours.  It is useful not only for assessing a proposed flying day, but also for reviewing its data on a day you have flown there and relate those data to your actual flying conditions.  This helps refine your interpretation of the data in the future.  A similar web site is Mallory Ridge, 7 miles ESE, elev. 2,040 ft.,

      Think of the wind talker, airport ATIS, your own weather observations at the site, your knowledge of the site, online weather info, etc., as each just a single piece of the big picture which you see clearly only when you put them all together correctly. 

Launches

      There are four sanctioned launches.  The main launch at Juniper Campground is at 2,900 ft. elevation.  It faces WSW.  The direct course to the main LZ is close to due west, which is where you see Mt. Tam on the distant horizon.  Appropriate winds are S to WNW.  Very light prevailing winds averaging no more than 5 mph from other directions are usually OK as long as you have favorable wind conditions for launching.  The launch has plenty of open space to either side and several hundred feet down, making it ideal for kiting practice and making top- and side-hill landings. 

      A second launch, at 3,200 ft. elevation, is on top of the main ridge next to Juniper and requires a short hike to reach.  Appropriate winds are SW-WNW, except when there are light N to NE winds; then you can launch off the back side.  In that case you fly to the left and over the gap to the main LZ.  You should not do this in N winds over about 10 mph due to lee-side turbulence and sink.  Yet you need at least 6-8 mph winds for launching because of limited run-out space.  The N side of this ridge is sketchy for soaring and has more potential for turbulence, so it is infrequently used. 

      The third launch, facing SE, is at the big parking lot just below the peak, elev. 3,700 ft.  It is not maintained and has some low brush on it making it difficult to lay out and inflate your canopy without line entanglements.  There is very little run-out space and there are utility lines about 400 ft. below launch, though they are easy to avoid.  Desirable winds are ESE-SSE between 6 mph and 12 mph. This area can be soared in the correct conditions, which are not very common.  If unsoarable after launch, you would turn right and follow the terrain heading toward the Juniper launch, then to the main or alt LZ.

      A fourth launch, the RDS tower, is technically open to PG’s but is not advisable for PG use.  It is at about 3,650 ft. elev. and faces NNW, toward terrain with no bail-out LZ’s; the nearest regular LZ is too far away to be easily reachable in a PG.  The terrain in this area of the mountain also generates greater turbulence because it has a lot more exposed dark rock.  This launch is essentially exclusive to HG’s.

      Ninety-nine percent of launches are from Juniper, and about 95% of landings are at the 1,000 ft. LZ, so the route between the two represents the standard flight plan. 

Landing Zones

      There are three sanctioned LZ’s.  The main LZ is 2.9 miles in from the North Gate entrance on North Gate Road.  There is a “1,000 Ft.” elevation sign just above the LZ parking pull-out.  This LZ is a large gently-sloped ridge that has enough space to land on easily.  We try to keep one or two wind streamer poles on the ridge top.  It is 1,900’ vertical below launch, and a 4.5:1 glide out, which means there is a greater risk of landing short than at most sites. 

      The alternate LZ is on the left/northwest side of the road about ¼ mile past the two ranches you will see on the drive up.  It has no markings or wind streamers.  Its main function is as a bail-out on north wind days when you cannot make the main LZ due to sink and/or headwind.  If you approach it in the usual direction, flying west, it has a slight down slope to it, so make S-turns or use big ears if necessary to get on the ground in the available space rather than float off the W end.

      The third sanctioned LZ is the helicopter LZ on South Gate Road.  It might be used if you’re trying to fly in the infrequent SE wind, launching from the SE launch near the peak.  It is rarely used by PG’s because they generally would not fly with a SE wind, and because there may be more turbulence at that LZ. 

Typical Flight

      Let’s look at a typical flight from Juniper launch.  The following is what you would encounter in sequence unless/until you find Your Big Thermal that takes you above it all.  The main ridge (Moses Rock Ridge), immediately to the right of launch, is usually the first place we look for lift.  Past that is a low gap or saddle which can harbor stronger venturi winds that can lead to a blowback, so be cautious about getting back in there too far with stronger winds.  Past this gap and farther west is a S-facing bowl that can sustain you in a S wind.  Alternatively, from the far end of the main ridge you might head WSW, over a low ridge that has weak thermals at both its upper and lower ends.  From there you might proceed NW across a narrow ravine (which often harbors sink and turbulence in WNW-N winds) into the West Bowls, located about 1/3 of the way down and to the right of a direct course to the LZ.  They are grass-covered slopes/bowls with almost no trees or high brush.  With patience you can often gain enough altitude there to make it back to launch for a top-landing.  However, if you’re still sinking you can fly SW to Poker Table Flat, a long ridge that roughly parallels much of the lower direct flight path from launch to the LZ.  Since it slopes down very little until just before reaching the LZ, it is a common land-out area.

      At some point after launch, especially in NW winds, you may find yourself in sink and/or headwind and unable to make the main LZ.  You must decide early to “bail” to the alternate LZ which is to the WSW from launch, or make a side-hill landing near launch.  Not doing so can easily lead to a land-out in the lower terrain which is usually safe but requires a lengthy hike out.  There is some brush/tree-covered terrain that must be crossed enroute to the alt LZ, a hazard mainly if you delay the decision to bail. 

Soaring Opportunities 

      Launch itself is a thermal source, and upslope winds move up the launch face and typically break free at or near launch.  This is why dust devils are occasionally seen at launch on active days.  The main ridge to the right (NW) of launch is usually the first place we try to soar.  The near end is foliage-covered and late in the day, with W winds, it often provides lift.  The far end is a steep spine that often harbors upslope winds that break free at some point to become a regular thermal.  On S-SW wind days, this far end also provides some ridge lift.  The terrain to the left (S) of launch is often soarable but is less steep and not as consistent as the main ridge to the right.  From this area it is easy to land sidehill or make it to the alternate LZ if necessary.  If you can climb a little from this area you can move back to a point over the big parking lot at the entrance to the Juniper campground; this is a thermal source.  The low ridge to the WNW of launch on the way to the LZ has thermal sources at the near (high) end and the far (low) end.  There are variable and inconsistent thermal sources in the West Bowls and they seem to work best in W-NW winds.  Poker Table Flat has thermal sources, especially the upper end adjoining the West Bowls and the higher of two knobs at the far end, near the LZ.  Once you’ve gained a few hundred feet over launch, there is lift over the main ridge next to launch, and at the top of the West Bowls.  Your on-site intro can point out these important landmarks to you. 

Common Weather Patterns 

      1.) Prefrontal conditions can bring smooth S-SW winds, sometimes with low cloud bases.  The lift can be widespread making it difficult to stay below a low cloud base.  If that happens, try to fly out away from launch and search for sink, as well as use descent techniques.  Depending on the strength and direction of the wind and its associated lift, you should fly only with adequate cloud base clearance, perhaps 200-300 ft. minimum over launch in light winds of 6-8 mph, and perhaps 1,000 ft. over launch in winds in the 12-14 mph range.  Be aware that the wind can increase rapidly in prefrontal conditions so land before risking a blow-back by high winds.  2.) Postfrontal conditions bring scattered cu’s, northerly winds and cold air. If the N base wind is low enough, i.e., under 5mph, there can be excellent soaring.  If convection cycles are too strong at launch during mid-day, wait until later when solar heating is less and cycle strength is lower.  3.) Interfrontal high pressure systems bring stable air masses, lighter winds and good weather.  Soaring is usually marginal, depending on the lapse rate at the moment.  It might be necessary to forward-launch.  In the colder months on stable days, fog often forms over the lowest terrain, so be sure to land before descending into it and losing your orientation.  On stable days in any season it is best to fly mid-day to take advantage of the maximum thermal strength from solar heating.

      Stable days are also known for inversions; sometimes there is a high inversion, say near launch level, and the soaring beneath it can be OK.  Other times, the inversion is low, near LZ, and you can find good soaring above it.  Generally, though, once you drop below the inversion you will likely sink out to the LZ.  Some weaker inversions can be “punched through”, especially when, as the day wears on, convection below an inversion increases, even as the inversion rises and dissipates, enabling a low save and a welcome climb back to launch, so it can pay off to try to stick with scratchy lift at the lower elevations.

        Sometimes a strong interfrontal high pressure center sets up somewhere over the far western states and  produces N to E winds of 30-60 mph at the peak, lasting 2-3 days, and shutting down PG flying for the duration.

      During the warmer months of the year, the marine air mass often makes its way inland to Mt. Diablo as an advection process driven by onshore wind.  It is a stratus deck usually based at 1,000-3,000’ msl and several hundred feet thick.  At the edge of this deck it is too windy to fly, but if this edge recedes back toward the coast during the day, the wind goes with it, often leaving good flying conditions, though the mixing of thermal action with marine air influence can be complex and a little chaotic.  When the edge of this stratus deck is between the Oakland/Berkeley hills and Las Trampas Ridge, conditions are frequently optimal for PG’s.      

Lee-side Winds

      Most lee winds are from WNW to ENE and we have a fair amount of experience with these winds.  Lee winds from E to SSE are less common, so we do not have much experience with those.  The following applies to the commoner first category, WNW-ENE. 

      It is OK to fly in lee-side conditions if you can reliably determine that these over-the-back winds are 5 mph or less.  You will likely not notice winds that low at launch or in the air.  In lee winds of 5-10 mph you may find launch to have upslope cycles that seem fine, but once in the air you may find areas of sink, turbulence, and disorganized thermals, often leading to a quick trip to the alternate LZ.  Lee winds over 10 mph are obvious enough at launch to indicate to most any pilot that it’s unflyable.

      If you find yourself in excessive lee-side turbulence after launch, fly away from the mountain toward the LZ’s where the turbulence and sink are less.

Land-outs

      At some point you will need to land out, despite your best efforts to follow the park rules and use only sanctioned LZ’s.  Land-outs should be made when you cannot confidently make an LZ, and to avoid landing in trees, high brush, rough terrain, or fog.  Land-outs are more common when the wind is in the WNW-N range because that’s what generates sink and/or headwind on the route to the LZ.  If you become familiar with the park trails and fire roads you can more easily choose a practical land-out spot with a mind to the subsequent hike out. 

Radio Use 

      Radio communication is more important at this site than most others because of the large area available for flying and the higher likelihood of landing out somewhere in this vast space.  If you land out, you can be difficult to locate just by sight, either from the air by other fliers, or from the ground.  Without radio contact and no visual confirmation of your status, no one can tell if you’re OK, and search efforts would have to be initiated.  Obviously, if your radio becomes inoperational while on-site, you could continue flying that day, but it would be advisable to apprise others so they can keep a special look-out for you.  Just do not make it a routine to fly without a radio. 

Flying With Hang Gliders  

      Hang gliders pioneered our site, starting in January, 1984.  Since PG’s came along around 1991 there have been no problems integrating the two, primarily because a.) we don’t often use the same launches or airspace, b.) there is such a large flying area available at the site, and c.) the overall number of both types is small compared to the number at other Bay Area sites.  Occasionally HG’s use the Juniper Launch when winds are SW.  They generally set up on the back part of launch (nearest the parking area) so there’s still plenty of room for PG’s to launch and top land on the front part of launch.  When PG’s approach to top-land, it is often necessary to pass close to HG’s setting up or in position to launch so allow plenty of clearance from them.  If possible, delay a top-landing when a HG is about to launch.  Otherwise, land sidehill away from the HG.  If the main ridge is working, then PG’s and HG’s will be flying close together there.  Many of the HG’s at Mt. Diablo are high-performance, with speeds about twice ours, or more, so maintaining separation is more of a challenge.  Ridge rules apply, and constant visual contact is vital, especially considering each other’s blind spots. 

X-C

      Occasionally conditions will be favorable for X-C.  Generally, these would include a light W wind and thermal tops at 5,000’ or more.  After you climb above 5,000’ a typical route would be to the SSE toward Blackhawk Ridge, then SE along the high terrain toward Windy Peak, Brushy Peak, and finally out toward Tracy.  If you fly south, avoid Livermore Airport’s Class D airspace and a Restricted Area between Livermore and Tracy.  Also stay above 800’ agl near the Livermore Lab.  Be sure to review and carry an aircraft sectional so you can locate and avoid these special airspaces.  If, as you’re just about to leave the park on this SE route and you are sinking out, the helicopter LZ is an appropriate place to land.  A second X-C route is directly over-the-back, to the E toward Discovery Bay or Byron Airport.     

      The park is surrounded by mostly private land, and the owners often do not want HG’s or PG’s on their property, complaining to the park staff when they spot us there.  Perhaps the best advice here is to land as discreetly as possible, and close to a road; then get off the property and onto the road with your gear immediately.

      You should have a dedicated retrieve driver or make some other arrangement for your vehicle since, after your X-C, you will likely not be able to get back into the park to get it before the park closes for the day, and it is a violation to leave it there overnight. 

      Before attempting X-C from Mt. Diablo connect up with someone who has experience with this when you can both be on-site. 

Restricted Airspace and Aircraft Traffic 

      The only restricted airspace within the Mount Diablo State Park borders is the outer ring of the San Francisco Class B airspace, the floor of which is at 6,000’ msl.  Its lateral boundary is about ½ mile E of the LZ and is oriented NW to SE at our site.  The airspace to the SW of this line and over 6,000’ msl is the no-fly area.  It is not a concern except on the rare days that you climb above that altitude and you are close to the main LZ. 

      Although Mt. Diablo is not close enough to the Concord Airport for paragliders to be at risk of penetrating its airspace (Class D, 2,500’ agl and 5 statute miles radius from the center of the airport), there is a lot of light airplane traffic to and from this airport passing near Mt. Diablo, so keep a good lookout to avoid these aircraft as best you can.

      If, while in the air, you hear sirens on the ground, there could be an evolving emergency, with a rescue helicopter soon to follow.  You should watch/listen for it, and if you detect it in the distance, land immediately.  Stay on the ground until it departs the area.    

      There are occasional sailplanes around Mt. Diablo and they usually operate from the Byron Airport which is 16 miles ESE of the peak. 

Surface Hazards 

      Spectators are numerous on week ends and when the weather is good.  They will often spread out and occupy much of the launch area to fly kites, throw Frisbees, watch HG’s/PG’s, etc.  Obviously, launching and top-landing pose a collision hazard to them and us.  When launching, politely advise spectators to stand well to the side in case a gust pulls you out of position.  Top-landing can be difficult and hazardous when launch is covered with spectators, so plan on a side-hill landing just below the top of launch to avoid a possible collision with them.  From the air on short final you can give a shout (e.g., “heads up!”) to alert nearby persons that you’re about to land.  Incidentally, try to be cordial to spectators and answer their questions. 

      Occasionally there are horseback riders passing through the launch area, and since horses can be spooked (possibly throwing the rider) by a launching/top-landing PG, you should delay operations until they’re out of the area.

      During much of the year, poison oak abounds, so be sure you can identify it so as to avoid contact with this plant while on foot.  Another obnoxious but non-toxic plant is tar weed, between mid-summer and late fall.  Its sticky residue gums up whatever it touches.  Fortunately, a couple of flying days after it abates for the season there is little to remind you of it on your equipment.  If you lay out your wing on the barren part of launch, you’ll avoid it there.  

      Rattlesnakes are also very common, including at launch and in the LZ’s, but they are a hazard mainly when you mess with them intentionally. 

      While driving, please be on the look-out for wildlife on the roads, including deer, coyotes, ground squirrels, snakes, lizards, and tarantulas, to avoid running over them.   

      Try to avoid flying near paved roads because of possible driver distraction. 

Conclusion

      Hopefully, this document will give you a good start in understanding Mt. Diablo, though the real learning comes from actually flying there.  Conditions at this site are variable enough to make almost every flight a learning experience, especially during your first couple of years.  Regular fliers there will acquire a wider range of knowledge and experience, making them feel more comfortable flying at other sites. 

      You should expand your range of self-allowed flight conditions very gradually.  For example, once you feel confident flying in winds of 6-8 mph near straight in at launch, try 10 mph next rather than jump right to 12-14 mph.  The same goes for less-favorable wind directions, lower cloud bases, restricted visibilities, stronger convection, and other challenging variables. 

      All of us who fly there agree that our mountain deserves respect, and if we always keep that in mind it will reward us with many memorable flights. 

      -Bob Clem, (email: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it ) with helpful review and suggestions from Rick Conger, Juan Laos, Robert Moore, Ann Sasaki, and Greg Thomas.  Relevant material for this document from other fliers will be considered for inclusion in future editions.