Wave at Avenal
December 2018

Avenal is known for its spring and fall convergence conditions, not for winter wave.  But we recently had usable wave and some very nice mid-winter flights.

Background

Theory of Favorable Conditions:  Classic, textbook standing wave conditions typically require winds that are more or less perpendicular to the ridgeline or cliff-line that will generate the wave.  From Avenal or New Coalinga airports, the ridges to the southwest and west from CA69 or to the west or north from C80 are aligned such that winds from the southwest could generate wave.  Of course, the winds need to be relatively steady, strong and increasing with altitude.  Wind velocity of 15+ knots at ridgetop, rising steadily to 50+ knots at 18,000’ MSL would fit the model.  The airmass should be reasonably dry through those altitudes so as to keep VMC and thus, VFR flights, but some moisture is useful in allowing cloud markers to form.  The Glider Flying Handbook has a short primer on wave weather at pages 9-16 to 9-19.[1]

Wave Forecasts Generally:  In addition to many sources of WX data available from government and commercial sources, we have three very useful soaring forecasts available to us for free, all based on Dr. Jack’s BLIPMAP template:

Alex’s Avenal Hi-Res RASP:  

http://canv.raspmaps.com/RASP/SIERRA/FCST/RASPtable.html 

This uses 0.9 km resolution and gives a very detailed picture of conditions within about 20 miles from Avenal.  It typically has forecasts for today and the next two days.

Bart’s Avenal RASP:  

http://avenal.raspmaps.com/index.php 

This uses 4.0 km resolution and covers our mountains from Monterey Bay down to Santa Barbara.  It typically has forecasts for today and the next two days.

Coastal RASP:  

https://rasp.nfshost.com/norcal-coast/ 

This is a regional map, extending up to Eureka and down to Ventura.  It typically has forecasts for today and the next six days.

These three sites often show the conditions differently, so it's good to check them against each other.  Each of these RASP sites shows forecast winds at 850, 700 and 500 mb, roughly corresponding to 5,000’ MSL, 10,000’ MSL and 18,000’ MSL.  Checking the wind direction and velocity at these altitudes, at various time intervals through the day, will give you a sense for whether favorable wave conditions may be coming.

Other sources of wind data include:

Windy.com
aviationweather.gov/windtemp
forecast.weather.gov/MapClick.php?lat=36.333&lon=-119.826#.XBscN817lPY
wrh.noaa.gov/mesowest/getobext.php?wfo=hnx&sid=AT565&num=72

Oxygen Requirements:  The FARs require supplemental oxygen at certain altitudes.[2]  Since Avenal is relatively close to sea level, a good deal of wave soaring can be available below those altitudes, even in gliders without supplemental oxygen.


Wave Conditions at Mid-December 2018

Several days of southerly winds were predicted.  On Wednesday, several members noted that OK conditions might exist on Friday and Sunday.  Here is a picture of the Friday forecast as shown on Wednesday (in this image, the number 1 is Avenal airport, 2 is New Coalinga, 4 is Black Mountain a/k/a Castle Peak:

The forecast for Sunday was also favorable, but increased moisture made it more likely that clouds would prevent good wave flying.

On Thursday, the forecast was less favorable, but Wyll Soll and Kevin Shaw (in IKS) decided to explore conditions from around 11 am to 2 pm.  The Friday morning forecast for noon that day showed this picture:

The winds aloft forecast was not ideal in that wind speeds at 850mb were good, but they decreased at 700mb and then increased modestly at 500mb. Surface winds at Avenal were very light. They launched from Avenal before 11:30 and contacted the wave at around 6,500’ downwind from Black after passing through sink at ~3,500’ and light rotor above that. That area of lift produced 2+ knot indicated climb for about 45 minutes up to just under 18,000’ and probably went a bit higher.  


As the picture below shows, there was a layer of high cirrus most of the day above, making it a little difficult to see clear/crisp lennies.

After topping out that climb near Black, they explored conditions north of New Coalinga and the east side of the San Benito range, but the lift was weaker and most of the time they were probably too far downwind.  Finally, they returned to the area downwind of Black and worked weakening lift for 30 minutes.  

Here is the flight profile from OLC:

Did the actual conditions match the forecast?  Generally, yes.  Wave was found in the areas shown in the forecast at the predicted times.  The cloud patterns did not match the forecast, but there were some clues from the high clouds, even though there were no classic lenticulars marking wave.  Winds were relatively light, never more than 40 knots even at 18,000’.  Overall, the day was better than expected in the sense that weak, but workable lift went up to 18,000’ and there was no trouble finding and staying in the lift.  

Morgan Hall notes that on days with a southwest wind, there is often a wave propagating from Tar Peak.  “Many days it is quite accessible right over the airport.  The secondary wave bar off Tar Peak typically ends up right over the runway and the highway.  It makes for easy ground reference tracking.”

Morgan also makes a more general point about the size and shape of the areas of lift in this area:

“[B]ecause of the steep face right at Black, that small area tends to produce a very strong bounce and it's highly localized.  I've had times when there is a spot right at the NW corner of the airfield that is producing 5kts when everywhere else is 2kts. You have to work it almost like a thermal it is so small, but it will often let you climb through to a whole different wave system.  This is actually pretty common for all of our local wave options.  We have lots of nooks and crannies that produce hotspots of lift where you can see 2x the average climb rate or more.”

The following image shows the potential complexity of the areas of lift and sink around Avenal, as downwind terrain features either magnify or nullify the shape and size and strength of the wave.


The forecast for Sunday was somewhat weaker, but still encouraging, especially since CCSC’s towplane was located at New Coalinga and relatively closer to some areas of lift encountered on Friday.  Here is a forecast for 2:30 pm:

The sky had ample evidence of wave in the morning before launch.

Wyll Soll (in WE) launched before noon and had another fine flight. He says:  

“One thing to note was that the wave down low (3000ft - 8000ft) was definitely stronger than it was above 9000 ft for the most part.  The only spot of good lift (more than 1.5 knots average) I found above 9k was directly behind Black.”  He also noted that the lenticulars did not correlate to the areas of lift in the classic manner.  

Here is the flight profile from OLC:

Aleks Radko had his ship already rigged at New Coalinga, so decided to explore the local conditions on Sunday as well.  He said:  

“I released at three thousand feet AGL just north west of Coalinga City and immediately climbing, thanks Jim for finding the lift.  After reaching around ten thousand six MSL, I decided to head upwind towards Black Mountain.  By the time I reached Black, I had lost around two thousand feet of altitude, and I was tracking only about twenty knots over the ground.  Just as I was thinking of starting to head in another direction, I found more lift and was able to climb to twelve thousand two hundred feet before deciding to call it a day and start heading back.  I think I could have kept on climbing higher and stayed up longer but two factors made me decide to start descending and heading back to the barn.  First, I didn't have my oxygen hooked up, and secondly I wanted to make sure that I had plenty of time to put away my glider in the box.”  Aleks’ flight illustrates the earlier point about not needing an oxygen system to explore the wave at Avenal  The flight profile from his .igc file is here:

 

Morgan Hall and Don Flinn (in 5H) launched around the same time and flew a remarkable, rectangular shaped cross-country flight.  They reported that, after their initial climb near the town of Coalinga and the old airport, their first leg up the San Benito Mountains was mostly in weak lift that was sufficient to sustain them cruising, but not worth stopping to work.  They had a good climb at the end of the first leg and then used ~5,500’ of altitude on the second, upwind leg.  Although there were ample signs of wave on that leg, none of them produced.  Their third leg down the Salinas Valley was easier in that the wave was well marked, and their route was just downwind of and parallel to the cap cloud on the upwind ridges.  Nearing sunset, their fourth leg was mostly a long final glide, but the wave was still working, particularly back near Coalinga.  The picture below shows the cap cloud over Black and the Avenal ridge, approaching from the west, with the Sierras in the far distance.

Morgan noted that today, the lenticular clouds were not particularly useful markers for lift, but that prospecting downwind from ridges and steep downwind rock faces, as well as rotor cu when lower, were more helpful to finding lift.  He also noted that winds were not particularly strong, but they did increase with altitude and produced many areas of weak lift.  The best lift was close to home:  “Strongest lift we saw on the way back to Coalinga was just SW of town right over a farmhouse in the canyon and directly downwind of a fairly steep face. That was probably 8-9kts at 4000 or so. There were workable bands of lift all the way down to 2000 or so. Not too much in the way of rotor either.”  

Although early in the day it was relatively clear, altitudes on the Sunday flights were limited by the cloud layers as shown in this picture:


Here is the flight profile from OLC:


Here is an image of the routes of all four flights:

Here are the local areas that produced wave on these two days, highlighted in yellow:

Also on Sunday, Ramy Yanetz (in TG) flew in wave south towards this area from Byron, and the southernmost point of Ramy’s flight roughly matched the northernmost point reached by Morgan and Don.  He said:  “Nice pre frontal wave albeit on the weak and wet side. Worked multiple wavelets while bumping against the upper level cloud deck. topped at 17K near Mt Diablo and proceeded SW to the Santa Cruz range and Mt Umunum, Hollister and Fremont Peak (wave wasn’t working there), climbed again at east ridge and chased a fake lenticular to Mercy hot springs and down to 8K, so turned around to have a chance to make it back to Byron before the rain starts. Landed with the first drops of rain. By the time I finished breaking down it was completely soggy. Fun winter wave day.”

Here is his flight profile from OLC:


Here are .igc files for the four flights and some other pictures:

https://www.dropbox.com/sh/hol1bwi5go5o48q/AACsNf74hWiWn6h59QA6vuF5a?dl=0 

Here are videos by Wyll, Morgan and Aleks:

https://www.youtube.com/watch?v=25IE2RUG0wk&t=1s 

https://www.youtube.com/watch?v=vJAWXm2CdPk&feature=youtu.be&fbclid=IwAR3cil4Mb4aDPj9vEQ79k4b6ie5HOO-KznWiglVawT_NvduAD6uzAWCown0 

https://www.facebook.com/aleks.radko/videos/pcb.787625388238673/787622638238948/?type=3&theater 

All the pictures and images in this document were provided by the pilots.

Conclusion

When pre-frontal southwest winds are forecast for Avenal, check the soaring weather predictions.  None of these pilots predicted the conditions would be as good as they turned out to be.  And they all enjoyed wonderful mid-winter flights.


[1]         https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/media/gfh_ch09.pdf 

[2]         91.211 Supplemental oxygen.

(a) General. No person may operate a civil aircraft of U.S. registry -

(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;

(2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen during the entire flight time at those altitudes; and

(3) At cabin pressure altitudes above 15,000 feet (MSL) unless each occupant of the aircraft is provided with supplemental oxygen.