WEATHER
Visibility: Very good. Some haze, but useful "haze domes" were present, even though there were no cumulus clouds in our area.
Wind: Morning and Early afternoon, out of the SE, Later became variable, switching direction and strength numerous times, as we were apparently under a convergence, which seemed to be over the field much of the afternoon.
Altitudes: Craig Gifford reached 10,200 MSL in 2-33 "Big Bird".
Time Aloft: Craig Gifford 4 hours, 19 min. in 2-33 "Big Bird".
Max Lift: 6-800 fpm.
Temperature: Very Hot.
Comment: There were numerous large dust devils in the area around Avenal today.
Tow pilot: Jan Zanutto
Pilots at Avenal Today: Tyler Bishop (2-33 with Harold), Harold Gallagher, Alex Caldwell, Mike Paoli (1-26), Joe Anastasio (PW-5), Martin Caskey (Nugget), Carl Engel (Russia), Morgan Hall and Julie Butler (Duo Discus), Carl's friend Mike Sherback (2-33 with Alex), Peter Mersino (2-33), Chris Reilly (2-33 in prep. for checkride tomorrow), John Harbick (first day out after getting private ticket 5 weeks ago), Craig Gifford (2-33), Ethan Ronat (PIK 20).
It was an unusually good soaring day for this time of year right over the field at Avenal today. I thought I would post some weather related stuff that may help explain what was going on, and also help newer soaring pilots see an approach you can use yourself to get an idea what the soaring weather may be like, either the night before you come out, or early the in the morning on the day you are flying. I have links to these things and more on the "Sierra RASP" site at http://canv.raspmaps.com/RASP/SIERRA/FCST/RASPtable.html
The Forecast Discussion, combined with the GFS computer model forecast plots for the 500 mb heights and "Vorticity", which also shows the "Steering Winds" at about 18,000ft., will give you a good idea of the overall larger scale "Synoptic" picture. In other words, what the larger size air mass movements and pressure center changes are doing that will be affecting the weather in our region. The RASP soaring forecast, which we all like to look at, does not show you this larger scale synoptic level picture, although the RASP is highly affected by the synoptic level situation. So, you should start by getting the overall synoptic level picture in your mind first, then you can go to the RASP.
Forecast Discussion from early this morning:
000
FXUS66 KHNX 091100
AFDHNX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JOAQUIN VALLEY - HANFORD CA
400 AM PDT SAT AUG 9 2014
.SYNOPSIS...
TEMPERATURES WILL REMAIN A LITTLE ABOVE NORMAL TODAY THEN LOWER
SLIGHTLY INTO EARLY NEXT WEEK. A FEW AFTERNOON AND EARLY EVENING
SHOWERS AND THUNDERSTORMS ARE POSSIBLE OVER THE SOUTHERN SIERRA
TODAY THROUGH MONDAY.
&&
.DISCUSSION...SATELLITE IMAGERY SHOWS MAINLY CLEAR SKIES PREVAIL
ACROSS THE CENTRAL CALIFORNIA INTERIOR EARLY THIS MORNING. WATER
VAPOR IMAGERY SHOWS A DEVELOPING UPPER LOW AROUND 40N/130W. THIS
LOW IS EXPECTED TO CONTINUE SOUTHEAST TODAY TO JUST WEST OF THE
SF BAY AREA. THE MODELS TYPICALLY STRUGGLE WITH THE EVOLUTION OF
CUT-OFF LOWS AND THIS IS NO EXCEPTION. BUT THE CONSENSUS AT THE
MOMENT IS FOR THE LOW TO ESSENTIALLY MEANDER JUST WEST-NORTHWEST
OF THE BAY AREA FOR A COUPLE DAYS. AN UPPER TROUGH FROM THE GULF
OF ALASKA IS THEN FORECAST TO KICK IT INLAND OVER CALIFORNIA ON
TUESDAY. SOME LINGERING TROFFINESS IS SHOWN OVER NORCAL WED-THURS
THEN FLAT RIDGING BY THE END OF THE WEEK.
LITTLE CHANGE IS EXPECTED TODAY AS TEMPERATURES WILL CLIMB TO A
A FEW DEGREES ABOVE NORMAL AGAIN. MUCH OF THE CENTRAL AND SOUTHERN
SAN JOAQUIN VALLEY WILL TOP THE CENTURY MARK. THE UPPER LOW SHOULD
DEEPEN THE MARINE LAYER ALONG THE COAST AND HELP NUDGE VALLEY TEMPS
DOWNWARD SLIGHTLY SUNDAY AND MONDAY...TO NEAR CLIMO. A BIT MORE
COOLING ON TUESDAY AS THE LOW MOVES INLAND THEN SLIGHT WARMING BY
THE END OF NEXT WEEK.
PWAT VALUES REMAIN AROUND 0.75"...A LITTLE ABOVE NORMAL FOR EARLY
AUGUST. DAYTIME HEATING WILL STEEPEN LAPSE RATES OVER THE SOUTHERN
SIERRA SUFFICIENTLY FOR ANOTHER ROUND OF CONVECTION TODAY. EXPECT
CUMULUS DEVELOPMENT OVER THE MOUNTAINS BY LATE MORNING THEN SHOWERS
AND MAYBE A FEW THUNDERSTORMS IN THE AFTERNOON AND EARLY EVENING.
THE UPPER LOW ITSELF IS FAIRLY DRY BUT COULD DRAW UP SOME MOISTURE
FROM NORTHERN MEXICO BY LATE IN THE WEEKEND. THE NAM IS SUGGESTING
THIS WITH SOUTHEAST MID LEVEL FLOW SPREADING MOISTURE IN OVER SOCAL
SUNDAY NIGHT AND UP TO THE SOUTHERN SIERRA BY MONDAY. THIS WILL HAVE
TO BE WATCHED AS IT COULD LEAD TO SOME NOCTURNAL CONVECTION SUNDAY
NIGHT. THE LOW MOVING INLAND ON TUESDAY WILL BRING A DRIER SOUTHWEST
FLOW ALOFT WHICH SHOULD END THE THUNDERSTORM THREAT. THE POSITION
OF THE LOW FAVORS NORCAL FOR UPPER DYNAMICS. BUT AGAIN...THESE LOWS
ARE DIFFICULT TO PREDICT AND A DRIFT FARTHER SOUTH ALONG THE COAST
COULD PLACE THE NORTHEAST QUADRANT OVER CENTRAL CALIFORNIA.
&&
.AVIATION...
A CHANCE OF THUNDERSTORMS ALONG THE SIERRA CREST AFTER 18Z SATURDAY.
OTHERWISE...VFR CONDITIONS WILL PREVAIL FOR THE NEXT 24 HRS.
&&
.AIR QUALITY ISSUES...
ON SATURDAY AUGUST 9 2014... UNHEALTHY FOR SENSITIVE GROUPS IN
FRESNO... KERN AND MADERA COUNTIES AND SEQUOIA NATIONAL PARK AND
FOREST.
FURTHER INFORMATION IS AVAILABLE AT VALLEYAIR.ORG
&&
.CERTAINTY...
THE LEVEL OF CERTAINTY FOR DAYS 1 AND 2 IS MEDIUM.
THE LEVEL OF CERTAINTY FOR DAYS 3 THROUGH 7 IS MEDIUM.
CERTAINTY LEVELS INCLUDE LOW...MEDIUM...AND HIGH. PLEASE VISIT
WWW.WEATHER.GOV/HNX/CERTAINTY.PHP /ALL LOWER CASE/ FOR ADDITIONAL
INFORMATION AND/OR TO PROVIDE FEEDBACK.
Note: The images you see below are "thumbnails". Click on the thumbnail images to enlarge to
full size.
This was the GFS 500mb heights and Vorticity forecast for 0000Z Sunday, which is actually 5:00PM
Saturday PDT. You can visualize the pressure patterns they are talking about in the Forecast
Discussion above by studying these.
The most interesting thing about the synoptic level picture today, that may have helped make today
somewhat better than average near our airport, is the low pressure area to the NW of us
combined with the higher pressure ridge to the east. The low may be bringing some cooler air
aloft over us and making the lapse rate steeper, which favors higher thermals, and also may be
breaking up the high pressure lid which usually limits thermal height over the San Joaquin Valley
by causing a strong temperature inversion at low levels. This was being referred to as a "cut off low"
in the forecast discussion. This cut off low pattern has been found to be favorable for soaring along
the Central California area over the years. It tends to linger for sometimes several days and brings
better laps rates than we have with the persistent high pressure lid over us with it's associated
subsidence and low level temperature inversion. Also, the on shore pressure gradients nearer
the coast were favoring pushing the marine air inland, and yet the ridge to the East of us was
tending to block the extent of the marine air intrusion, so we may have been in just the right
area to favor having the convergence zone right over us. Often the convergence zone is further
to the west of the airport, and harder to reach from Avenal with a low performance glider.
But today, the convergence was right over the field most of the later part of the afternoon and
you could get right into it directly from a 2,000 ft. tow.
Satellite Images can be helpful for visualizing the synoptic picture described in the forecast discussion, particularly the Water Vapor images, which the professional forecasters seem to use a lot, along with the computer model forecasts, such as the GFS (Global Forecast System), the NAM (North American Mesoscale) and the ECMWF (European Center for Medium Range Weather Forecasting). Recently a new model called the HRRR (High Resolution Rapid Refresh) became available. The GFS usually works pretty well, and most of the time the computer models tend to agree, but occasionally they do not. The forecasters will often comment on these computer models in the forecast discussions, so it's fun to try to become familiar with what they're talking about.
Once you get the "big picture" from the synopsis, it's time to start looking at the RASP.
These plots are from Bart's Avenal RASP. You could have seen these on Friday night, or early this morning before heading for Avenal:
The Boundary Layer Top plot shows you the highest level the thermals are expected to go. This one is for 1400 PST, or 1500 PDT. The BL Top usually can not be reached by the average Joe glider pilot in a 2-33, I won't mention any names. However, I often find that if I ask the top pilots in their glass and carbon fiber ships how high they got on a given day, again, I won't mention any names, they very often reach almost exactly what the maximum BL Top forecast is on the RASP. For orientation, Avenal is No. 1 on the map, and Coalinga is No. 2.
This is the surface level wind plot from the RASP. Winds are quite important in our soaring, as the local winds combined with the effects of terrain, have a strong association with areas of "convergence", which is generally very desirable, as it is associated with stronger lift and lift that is lined up that can be "run" to cover a lot of ground with less need for stopping to circle. Strong winds tend to break thermals up into bubbles and disorganized turbulence, and are generally considered a negative for thermal soaring. Lighter winds are more favorable to thermals in general. Winds also very important if you are considering using ridge lift and avoiding sink associated with wind blowing downslope.
The next plot is what Dr. Jack, the inventor or the RASP calls "BL Max Up/Down Motion". That is "Dr. Jack speak" for what most of us now call "Convergence". In the old days we used to call this same thing a "shear line". You will hear those last two terms frequently around glider pilots. You will not likely hear "BL Max. Up/Down Motion", unless maybe Dr. Jack is visiting! Values above zero are good, and indicate lift from convergence. In all Dr. Jack's plots warmer colors tend to be stronger or often "good", and cool colors tend to be lower values and often "bad". The exception may be winds, where warmer colors indicate stronger winds, which is usually bad for thermal soaring, but may be good for wave soaring.
You can see an interesting phenomenon related to the convergence line in this Plot. If you look south of Avenal, where the Cottonwood pass allows marine air to spill through the mountains, you can see the yellow colored convergence line bowing out to the East towards the central valley, probably east beyond I-5. This happens pretty frequently. So if you are coming back from the south towards Avenal, you may have to detour out to the East from the straight line course back to Avenal in order to say in the convergence line. The area to the west of the bowed out area will likely be marine air that is more stable and likely to be devoid of thermal lift. If you look further north up by the Pacheco Pass area, you will see an even more pronounced bulging of the convergence to the East. It bulges out east to the point where it appears the convergence line is completely blown out or disrupted to the east. This correlates with the much stronger winds coming through the Pacheco Pass compared to the Cottonwood Pass at this time.
The next plot shows Thermal updraft velocity plotted along with what is called, in Dr. Jack Speak, the "Buoyancy Shear Ratio". In more plain English, what this tries to show is whether wind will be so strong as to cause the thermals to be broken up into bubbles or turbulence that is difficult for soaring pilots to use (bad). Or, looking at it the other way, whether the wind will not be strong enough to to the same (good). If you see areas that appear stippled (there are two
degrees of stippling intensity), expect that the wind will be strong enough to cause the thermals to be "broken up" or changed into difficult to use bubbles and turbulence rather, than nice steady chimney-like columns of rising air.
Another very useful plot is the "Cu Cloudbase where Cu Potential > 0". Don't be put off by the Dr. Jack speak title. This is one of the most useful of the RASP blipmaps. What it basically shows is if there will be cumulus or not, and if there are cumulus clouds, what will be the altitude of the cloud base. You can see from this plot that it was clear over the Avenal area, but to the South around the New Cuyama area, there were forecast to be cumulus with a cloudbase of approximately 10,500 MSL. Morgan and Julie were considering making a run towards these clouds, which Morgan discusses below.
This is a Skew-T/LogP sounding forecast for Avenal Airport at 1400 PST. Weather balloons are sent aloft at certain locations and actually directly measure the temperature, dew points and winds at altitude, and radio these values back to the National Weather Service. This Skew-T plot produced by the RASP is a FORECAST of what such a balloon would measure IF you were to release one at this time of day. You can extract much useful information from these Skew-T forecasts once you learn how to read them. They also can show the levels of high level clouds, such as cirrus clouds, which do not show on any of the other RASP plots, but which can affect the heating at the surface and the accuracy of the RASP forecasts. If there is likely to be precipitation, it will also show in these RASP Skew-T plots. This particular Skew-T plot however, does not show any high level clouds or precipitation. It also does not indicate that there will be any cumulus clouds or over-development type of clouds, such as overcast or thunderstorms. In other words, it is saying the sky will be clear, which it was!
Below is another RASP Skew-T sounding forecast for the same date and time as above, but for the Mt. Whitney area, where there were some large cumulus build ups. You can see how when there are cumulus, the temperature and dewpoint lines will tend to merge at the altitude where the cloudbase is forecast. You can also see a black box like area on the left side and inside that a small green line. The black area indicates the altitude and thickness of the cloud layer. The green line area indicates there could be precipitation. Precipitation may not reach the ground. Or it could be snow if the conditions are right.
 |
| Craig on his way to 10K. |
Craig's in flight instrument panel and left foot "selfie" as he breaks 10,000 MSL.
Alex congratulates Craig Gifford after his epic flight in "Big Bird". He had planned ahead and took extra water with him. He was very high, appearing as just a small yellow dot from the ground much of the time, but he remained within safe gliding distance of the field. He made a perfect cross wind landing on runway 31 at the end of his flight. Craig had the longest flight of the day. He is now the leader for the prestigious Central California Soaring Club "Iron Butt" award for the year. The award will be presented to the eventual winner at the Club Barbeque later this Fall. If he had stayed up 41 minutes longer, he would have earned the Duration leg for an FAI Silver Badge. Maybe next time, once the blisters and pressure sores heal up!
Craig's comments: "
I started at 1:56pm and landed at 6:15pm. 4 hours 19 minutes. Thank you so much for staying and helping me tie down." He also told me he had been in thermals with Morgan and Julie in their DUO, Martin Caskey in his Nugget and with Carl in the Russia at various times during his flight. He got down to 2000ft MSL at one point, and was preparing to land, but then got a boomer and climbed back up to over 10,000 ft. MSL where he stayed for another 2 hours or more.
Carl Engel had a nice flight in the Russia again. He made 2 laps around a course from Avenal to Coalinga and return. He made a beautiful take off and landing in the Russia. Carl's friend Mike Sherback went for his 2nd intro flight with Alex in Big Bird, and did quite well, flying much of the tow on his own with a small amount of assistance, and doing the pattern and landing on his own with a bit of verbal coaching. He is a rated power pilot, and owns a Cessna 172, in which he and Carl flew to Avenal today from Palo Alto.
 |
| Martin's first flight in TN. |
Martin Caskey flew his gorgeous Nugget for the first time today, twice. He has been working on it for a long time, and it really shows. He has it prepared beautifully, with Transponder, FLARM, GPS moving map, and very interestingly, he has daylight visible LED strobes on the turtle deck and underneath the fuselage. The first flight was short, but on the second flight, he was up for a LONG time, and reached over 10,000 ft. MSL, if I recall correctly. After landing, he tried to present us with his usual blase, quiet, ho-hum, just another aircraft, just another flight, supremely competent persona, but we could tell when he landed that he was "STOKED"! Here Martin and his good friend Rex are beginning to disassemble the Nugget after Martin's great flight.
Julie Butler helps Ethan Ronat with the door on his trailer after she landed in the DUO at the end of a nice flight with Morgan. Morgan and Julie initially flew South from Avenal, and were considering a possible flight around the lower end of the San Joaquin Valley followed by a run up the Sierras. However, Morgan reported the lift was not very good to the South, so they decided to run North instead, and got up as far as the Panoche area from what we groundlings could see on their SPOT tracker. I wonder if when they made the run to the South, they could have been on the West side of the Eastward bow seen on the BL Up/Down RASP (Convergence) blipmap? Perhaps there was some marine air coming through the Cottonwood Pass influencing things down in that direction?
Morgan's Comments on Down South and the day:
Great background on the weather and the systems in general from Alex.
I had hopes and aspirations of flying south, connecting with the clouds at 12K+ near Cuyama and then running up the Sierra. Earlier in the week the forecasts looked good for such a run. The closer we got to Saturday, the less positive the local forecast was.
It can be a tough jump from Avenal to New Cuyama. Usually the crux is between Avenal and California Valley. Our typical route usually involves following a convergence line from Black Mountain down towards the west side of the CA Valley and possibly on to the La Panza range.
Yesterday had no forecast convergence until maybe on the Temblors. But lift in the 5-6k range seemed likely on the high ground so it wasn't an impossible task to attempt. The RASP missed the call on the winds aloft. We were seeing 10-12kts out of the South very consistently early in the flight.
Interestingly enough, this didn't seem to be "marine air" early on. Just a southerly flow ahead of the true marine push. Down near Orchard Peak, Cottonwood Pass and Paramount, dust from tractors was showing 5-10kts on the ground from the S/SW. There were dust devils forming, broadly spread out. Unlike a typical convergence line where they will be fairly clustered. The lift just didn't go very high. Probably just enough wind to keep the surface heating down and limiting the top of the lift. 4000ft was about it.
After an hour, we were only about 25 miles out from Avenal. In order to make the run around Tehachapi and get connected on the Sierra, you've got to average at least twice that speed for the first couple of hours. It was clear we weren't going to get established on the Sierra with enough heating to get a very high climb to final glide back to Avenal. The reports from the Sierra pilots were indicating it was a pretty easterly line with heights only in the 14k range on the Southern Sierra. A few reports of 15.5k were coming in. Not a booming day with 19k cloudbase or anything.
Given the soft conditions near Paramount and the likelihood of a marine push later making it tough to get back across the 41/46 passes, we turned around. An hour in 100 degree heat can be draining as well and hard to keep up on hydration.
On the way back Julie found the convergence line west of the airport. Climbing from 6k to 8k straight ahead we turned and headed NW playing the "how long before I have to circle" game in the convergence. Eventually the line got weaker and hard to follow and it took a few turns up near EL5 to stay comfortable. On the way back I took a good 5kt climb in order to make the 30 mile final glide at 90kts.
We of course got back right as the convergence was hammering Avenal. That's when we climbed out with Craig a little bit and let the winds organize on the ground before landing. He took the boomer to 10k right over the field as the convergence rolled through and peak heating at 5pm occurred with 105 temps on the ground.
