Weird mountain draft

[JimB]

So my wife and made it to the Bahamas and back last week. What a great trip and I'll try to put a writeup in the vacation section soon. However this is related to the flight down there. We left early last Sunday morning and were crossing our highest peak (5400') around 0815 at 9500'. We were just talking and looking out the windows at the morning sun on the mountains when all of the sudden I felt the aircraft pitch up and slow down as the AP tried to compensate for some sort of draft. It didn't last long but it sure got my attention. There was no significant weather in the area and the winds aloft weren't even that strong. We were also around 4000 feet over the highest peak. It was just odd. Anyone experience this before? I have read all about mountain winds and up/down drafts but this just didn't seem to fit that. Here is a link to the flight.  

https://flightaware.com/live/flight/N1969F/history/20220410/1019Z/KTYQ/KBHC

 

[Rwsavory]

Wave action can occur far above the ridge line. I've flown up to about 19,000 ft in a sailplane near Mt. Mitchell, NC, although the winds were pretty strong at the time.  We've also experienced wave lift/sink far away from the hills at times. 

[N201MKTurbo]

I flew right through there 4 weeks ago.

I looked at your track log and only saw about 10 knots of speed reduction. I have been in mountain wave sink and rising air that required 30-40 KTS of speed change to maintain altitude. Not that unusual or very strong. But we have mountains all over the place, so it is just flying around here.

[JimB]

Ok. It wasn't something that really bothered me. I just thought I was high enough to stay out of it. Thanks

[Unit74]

Sounds like a bit of mountain wave.  I’ve had that happen to where I eat uncommanded climbs and descents. I asked center for a block altitude.  Actually, I told them I was going to use it it as I was unable to compensate for the changes.  If they were gonna violate me, I’d have to drag Mother Nature in as a character witness. 

[PMcClure]

Been in a mountain wave flying home from Charlotte. 50-70 miles from the mountains and 2-3k above the highest peak. Saw an airspeed of 90 knots (in my F) before killing the AP and riding the wave. Was shocked to see that speed difference so far from the mountains.

[GeeBee]

I've been in wave so bad I've went everywhere from overspeed clacker to near stick shaker all in a matter of miles. One time I had to give the airplane its head, just to keep from stalling. The worst and most well known waves are over Northern Iran. The other day, I was out near KMTV with 65 knots winds, really caught a roller at 11,000, 100 KIAS to 180 KIAS. I popped the speed brakes because I was worried I would get spit out into some significant turbulence at 180 KIAS.

[Hank]

Flying home from Sun n Fun to WV, I hit turbulence and mountain wave well south of Asheville, and I was at 11,000 msl. It was like being in a washing machine for 30-40 minutes; once we got past the big hills, everything smoothed out nicely.

[Will.iam]

Passing rockies at 38,000 and got a mountain wave that popped us up to 40,000 with the captain pulling the thrust back to idle and me asked for a 10k block altitude in a DC-8. Next thing we knew captain was fire walling the thrust as we came off the lift into a sinker and got spit out at 35,000. Loadmaster went back to check the pallet loads to insure none had worked loose or popped chains. Then he showed pictures of the lav that had toilet water all splashed up on the walls. Nasty. 
So no altitude is safe from a mountain wave and that experience in the back of my mind haunts me anytime i get close to a mountain in the mooney. 

[Unit74]

12 hours ago, PMcClure said:

Been in a mountain wave flying home from Charlotte. 50-70 miles from the mountains and 2-3k above the highest peak. Saw an airspeed of 90 knots (in my F) before killing the AP and riding the wave. Was shocked to see that speed difference so far from the mountains.

That’s where I got caught in it as well. 15 minutes worth. 

[EricJ]

The highest I've been in my airplane was 17500 riding a mountain wave while crossing the pass by Angel Fire in NM.   It was still climbing pretty well (No Turbo!) and the only reason I stopped was that I was VFR and didn't want to bust the Class A.   Felt it like it would have kept going for quite a while.  I had had to maneuver around a bit through the downdraft parts prior to that while approaching the ridge on the east side.

 

[Scott Dennstaedt, PhD]

On 4/18/2022 at 4:34 PM, JimB said:

So my wife and made it to the Bahamas and back last week. What a great trip and I'll try to put a writeup in the vacation section soon. However this is related to the flight down there. We left early last Sunday morning and were crossing our highest peak (5400') around 0815 at 9500'. We were just talking and looking out the windows at the morning sun on the mountains when all of the sudden I felt the aircraft pitch up and slow down as the AP tried to compensate for some sort of draft. It didn't last long but it sure got my attention. There was no significant weather in the area and the winds aloft weren't even that strong. We were also around 4000 feet over the highest peak. It was just odd. Anyone experience this before? I have read all about mountain winds and up/down drafts but this just didn't seem to fit that. Here is a link to the flight.  

https://flightaware.com/live/flight/N1969F/history/20220410/1019Z/KTYQ/KBHC

 

Jim,

Likely some kind of wave activity given the upwash you experienced. That's really the only plausible explanation given your position over the mountains. There was primarily zonal flow over the region which gives you the proper wind direction and there was a good stable layer at the surface to help induce some gravity waves. The unstable air above will certainly help propagate those waves upward to your altitude.

But what stands out the most is the negative omega from about the ridge tops up to your altitude.  This describes air that is moving away from the earth. It's not very high by any stretch of the imagination.  Doesn't really tell you specifically there is mountain wave activity in the region, but it certainly doesn't eliminate the possibility. I'm guessing that if you were 1000 feet higher you may have not experienced any upwash and if you were 1000 to 2000 feet lower you might have experienced a bit stronger upwash. I'll be discussing some of this in my new book, The Skew-T log (p) and Me that should be available in eBook format before AirVenture.  Hope this helps.

 

    

[rbp]

You can havevwave anytime winds are moving (close to ) perpendicular to the ridge, and as far downwind as 200 miles. 

[rbp]

2 hours ago, Scott Dennstaedt, PhD said:

Jim,

Likely some kind of wave activity given the upwash you experienced. That's really the only plausible explanation given your position over the mountains. There was primarily zonal flow over the region which gives you the proper wind direction and there was a good stable layer at the surface to help induce some gravity waves. The unstable air above will certainly help propagate those waves upward to your altitude.

But what stands out the most is the negative omega from about the ridge tops up to your altitude.  This describes air that is moving away from the earth. It's not very high by any stretch of the imagination.  Doesn't really tell you specifically there is mountain wave activity in the region, but it certainly doesn't eliminate the possibility. I'm guessing that if you were 1000 feet higher you may have not experienced any upwash and if you were 1000 to 2000 feet lower you might have experienced a bit stronger upwash. I'll be discussing some of this in my new book, The Skew-T log (p) and Me that should be available in eBook format before AirVenture.  Hope this helps.

 

    

Do you think this was thermals? As far as I know, skew-t only represents thermal activity, not wave?

[Scott Dennstaedt, PhD]

3 minutes ago, rbp said:

Do you think this was thermals? As far as I know, skew-t only represents thermal activity, not wave?

100% not thermals.  The lapse rate in the lower part of the atmosphere at 8 a.m. was very stable...notice the fog layer as well.  If this were later in the afternoon and he was at the top of the boundary layer, possibly.  The Skew-T is often used to determine the potential for mountain wave activity as I will describe in my next eBook.  For this case, it was not a "classic" vertically-propagating lee wave signature.  

[Scott Dennstaedt, PhD]

10 minutes ago, rbp said:

You can have a wave anytime winds are moving (close to) perpendicular to the ridge, and as far downwind as 200 miles. 

Actually that is not the recipe for mountain waves.  Certainly wind speed and direction are important, but stability to create the negative buoyancy is part of the recipe.  

[rbp]

2 minutes ago, Scott Dennstaedt, PhD said:

100% not thermals.  The lapse rate in the lower part of the atmosphere at 8 a.m. was very stable...notice the fog layer as well.  If this were later in the afternoon and he was at the top of the boundary layer, possibly.  The Skew-T is often used to determine the potential for mountain wave activity as I will describe in my next eBook.  For this case, it was not a "classic" vertically-propagating lee wave signature.  

I always look skew-t  for thermals Rather than  Convergence or wave, which is why I asked. I am curious to know how they apply to wave

[rbp]

1 minute ago, Scott Dennstaedt, PhD said:

Actually that is not the recipe for mountain waves.  Certainly wind speed and direction are important, but stability to create the negative buoyancy is part of the recipe.  

wind speed and direction are necessary conditions, no? May not be the whole recipe but without them , not having any wave

[Scott Dennstaedt, PhD]

4 minutes ago, rbp said:

wind speed and direction are necessary conditions, no? May not be the whole recipe but without them , not having any wave

Yes, as I mentioned, wind speed and direction are important, but they are just one ingredient in the gravity wave recipe.  

[thinwing]

interesting discussion...mountain wave activity is mostly wind and direction factored ,and  were the major factors we considered for wave flight over Minden Nv.We would look for a pacific storm system producing strong winds (35 mph in this case)coming directly perpendicular from the ridge tops @ 10k to 11k .Freel peak in this case..producing strong roter at and below peak alitude and strong mountain wave lift from  12oo to 2000 fpm climb rate above.This lift was frequently very smooth and 5 to 10 miles down range for the primary wave,Secondary and terterary etc continued as much as 100 miles down range.Lift could continue well into the flight levels and have resulted in several world alitude records.I was able to earn all 3 lennies (tripple lennie) award in just one flight...very cold though and required 100 % o2 out of a4 regulater.My flight was well north of 30k and could have continued the climb , but ATC would not approve further expansion of my wave window waiver (non transp ,vfr flight into class A airspace).

[rbp]

8 minutes ago, thinwing said:

interesting discussion...mountain wave activity is mostly wind and direction factored ,and  were the major factors we considered for wave flight over Minden Nv.We would look for a pacific storm system producing strong winds (35 mph in this case)coming directly perpendicular from the ridge tops @ 10k to 11k .Freel peak in this case..producing strong roter at and below peak alitude and strong mountain wave lift from  12oo to 2000 fpm climb rate above.This lift was frequently very smooth and 5 to 10 miles down range for the primary wave,Secondary and terterary etc continued as much as 100 miles down range.Lift could continue well into the flight levels and have resulted in several world alitude records.I was able to earn all 3 lennies (tripple lennie) award in just one flight...very cold though and required 100 % o2 out of a4 regulater.My flight was well north of 30k and could have continued the climb , but ATC would not approve further expansion of my wave window waiver (non transp ,vfr flight into class A airspace).

My experience with people writing a book, is that it doesn’t pay to argue with them

[Scott Dennstaedt, PhD]

1 hour ago, rbp said:

My experience with people writing a book, is that it doesn’t pay to argue with them

Unless you want to learn something...  - I've been doing this for 42 years, so the book is long overdue. 

[rbp]

So you want people to argue?  don’t understand 

[Scott Dennstaedt, PhD]

15 hours ago, rbp said:

So you want people to argue?  don’t understand 

There are a couple definitions of argue -

1) Yes, it is important to argue based on the definition to "give reasons or cite evidence in support of an idea, action, or theory, typically with the aim of persuading others to share one's view."

2) Not good to argue to "exchange or express diverging or opposite views, typically in a heated or angry way."

Disagreement or opposing views is normal and it is often a great way for people to learn about a topic if done in a civilized way (see definition #1). It has certainly taught me a lot about what I should and should not be teaching pilots when it comes to weather. Most pilots have a very skewed view of the discipline and the recipe for mountain waves is one of them.

If you haven't read it, Think Again by Adam Grant is an excellent book on this subject. Hope that make sense? 

[cferr59]

I flew from Tampa to Philly via SAV on Sunday and there were significant up and downdrafts through the area from Fayetteville to Norfolk. ATC was referring to it as waves. There was a glider up at 13k.  It was difficult to hold altitude and resulted in significant variations in IAS. I gave up and requested a block.  I was at 7000 feet and aircraft below and above me were experiencing similar.