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Mountain Flying and Winds Aloft Discrepancies


aggiepilot04

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Howdy all,

 

Flatlander here, looking for some advice from some of you frequent mountain flyers.  I've flown into the mountains a handful of times (Leadville, Granby, Gunnison, Steamboat), and I've also diverted into Denver a few times.  All of these have been very easy go/no go decisions though....conditions were pristine (VFR with calm winds) or a death trap (ifr + icing + windy).  Yesterday, however, I was trying to get into Kremmling, and the decision was much more difficult.  An early morning brief forecasted 7kt winds at 12,000 ft at the time of my arrival.  En route, the G1000 (XM) was showing 45kt + winds at 12,000 ft.  ADS-B on my phone (Garmin Pilot/GTX345) was showing 22kt winds at 12,000 ft, and, for some reason, winds aloft were unavailable on my iPad.  AWOS reporting at various passes/peaks varied from 7kts at some locations to 27G41 at others.  AWOS at Kremmling was reporting 11G17 (30 degrees off centerline, if I remember correctly).  There were no PIREPs relevant to my route of flight at the time.  With each handoff between controllers, I requested ride reports...and no one was complaining up until my last handoff.  Ultimately, I decided to divert to BJC for 2 reasons: 1) I didn't like what the ride was starting to feel like at FL180 approaching the mountains and 2) a 737 had just reported moderate turbulence climbing through 17,000 out of Denver.  The turbulence that I encountered was light, but I still had the sensation of being tossed about like a kite despite the pitch/roll changes being very slight.

 

Anyways, point being, I have several questions/takeaways from yesterday's flight...in no particular order:

  1. I need to better understand the sources of the data that I have in the cockpit and why they could vary so significantly.
  2. While I think I have enough basic knowledge and understanding of mountain flying to safely complete a flight in pristine conditions, I need some time in the cockpit with a mountain instructor to be better equipped to make decisions in more marginal conditions.  I'm likely losing some of the utility of the airplane by making no go decisions that are too conservative.  
  3. I would like to better understand how some of you more experienced mountain flyers use the available weather products to make your go/no go decisions.  Any practical/real world examples that you can provide would be helpful.
  4. Has anyone else seen such significant differences in winds aloft information?  Obviously some of the data on the G1000 is interpolated, but I still don't understand why it could vary as much as it did.

Thanks in advance.

Edited by aggiepilot04
typo
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The problem 

26 minutes ago, aggiepilot04 said:

An early morning brief forecasted 7kt winds at 12,000 ft at the time of my arrival.  En route, the G1000 (XM) was showing 45kt + winds at 12,000 ft.  ADS-B on my phone (Garmin Pilot/GTX345) was showing 22kt winds at 12,000 ft, and, for some reason, winds aloft were unavailable on my iPad.  AWOS reporting at various passes/peaks varied from 7kts at some locations to 27G41 at others.  AWOS at Kremmling was reporting 11G17 (30 degrees off centerline, if I remember correctly).  There were no PIREPs relevant to my route of flight at the time.  With each handoff between controllers, I requested ride reports...and no one was complaining up until my last handoff.  Ultimately, I decided to divert to BJC for 2 reasons: 1) I didn't like what the ride was starting to feel like at FL180 approaching the mountains and 2) a 737 had just reported moderate turbulence climbing through 17,000 out of Denver.  The turbulence that I encountered was light, but I still had the sensation of being tossed about like a kite despite the pitch/roll changes being very slight.

Sounds normal. Without doing a full course (I used to teach this stuff), here's some concepts which might help:

1. No winds aloft are forecast for within 1,500' of station elevation. There's a reason - at that altitude and below, even flatland surface terrain and structures affect the wind enough to make the winds aloft irrelevant.  On your route, a lot of terrain is 1,500' below those Denver 12,000' winds aloft. The winds aloft, where forecast or actual, were pretty much irrelevant. Your Garmin, OTOH, was reading the actual "surface winds" and the AWOS were definitely surface winds.

2. Mountains funnel and change the velocity and direction of winds far more than flatland surface features. Best visual image I know of is whitewater. The water enters rocky terrain at a certain speed but the movement over around, and through tyhe rocks changes both its direction and velocity. The reason for the common 25kt 12,000' winds aloft limitation for flying in the mountains is not the 25 kts; it's what the surface does to those 25 kts.

I'd highly recommend Sparky Imeson's Mountain Flying Bible or a visit to Denver when the Colorado Pilots Association does its mountain ground school, in June and August. Well worth it if you are heading there regularly. They also have a group of highly qualified instructors if you choose to do the flight portion.

Edited by midlifeflyer
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3 hours ago, midlifeflyer said:

The problem 

Sounds normal. Without doing a full course (I used to teach this stuff), here's some concepts which might help:

1. No winds aloft are forecast for within 1,500' of station elevation. There's a reason - at that altitude and below, even flatland surface terrain and structures affect the wind enough to make the winds aloft irrelevant.  On your route, a lot of terrain is 1,500' below those Denver 12,000' winds aloft. The winds aloft, where forecast or actual, were pretty much irrelevant. Your Garmin, OTOH, was reading the actual "surface winds" and the AWOS were definitely surface winds.

2. Mountains funnel and change the velocity and direction of winds far more than flatland surface features. Best visual image I know of is whitewater. The water enters rocky terrain at a certain speed but the movement over around, and through tyhe rocks changes both its direction and velocity. The reason for the common 25kt 12,000' winds aloft limitation for flying in the mountains is not the 25 kts; it's what the surface does to those 25 kts.

I'd highly recommend Sparky Imeson's Mountain Flying Bible or a visit to Denver when the Colorado Pilots Association does its mountain ground school, in June and August. Well worth it if you are heading there regularly. They also have a group of highly qualified instructors if you choose to do the flight portion.

Thanks for the info.  I understand most of that at a conceptual level, and I have read the Mountain Flying Bible.  While I don't have much experience mountain flying, I do understand how to take the wind direction and try to visualize how it flows around the mountains.  I *think* I can derive where the updrafts/downdrafts may be present based on that, but I don't have the experience yet to know for sure what I'm visualizing is accurate because I've never found myself in a downdraft.

I guess what I'm asking is for a real example with real numbers of when you would make a no-go decision solo, and when you'd make a no-go decision for passenger comfort (I had a buddy with me yesterday who was clearly uncomfortable in light turbulence, so that made my decision somewhat easier).  And if it's questionable/marginal (say, exactly 25kts), would you start into the mountains anyways and feel it out?  Based on the information that I had, would that be a go or a no-go for you?

Edited by aggiepilot04
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Hard to say. Those forecasts of 7 kts at 12,000' suggest no problem, but the 45 kt XM winds (which I would avoid) suggest there was something else going on. Without a much bigger weather picture, I can't make a go-no go decision or, if go, whether I would modify the route (windward rather than leeward where possible for example).

diverting when in doubt is always a good idea.

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23 hours ago, midlifeflyer said:

Best visual image I know of is whitewater. The water enters rocky terrain at a certain speed but the movement over around, and through tyhe rocks changes both its direction and velocity. The reason for the common 25kt 12,000' winds aloft limitation for flying in the mountains is not the 25 kts; it's what the surface does to those 25 kts.

The whitewater analogy is a good one. The worst turbulence I’ve encountered was on a bluebird day with light winds aloft. Leadville Awos was 11G17, that should be fine, but where were the gusts coming from? Think of the valleys as large lakes, with the passes where that water will flow over & down. When you check the barometer setting from one valley to the next you’ll see what I mean. 

This will happen usually late morning until early afternoon. That & convective activity is why most mountain flying is done early in the day. 

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5 minutes ago, jackn said:

The whitewater analogy is a good one. The worst turbulence I’ve encountered was on a bluebird day with light winds aloft. Leadville Awos was 11G17, that should be fine, but where were the gusts coming from? Think of the valleys as large lakes, with the passes where that water will flow over & down. When you check the barometer setting from one valley to the next you’ll see what I mean. 

This will happen usually late morning until early afternoon. That & convective activity is why most mountain flying is done early in the day. 

My worst turbulence was on a day when the winds were substantially stronger. We were returning to Denver from Santa Fe (partial route approximation on SkyVector).  Because of the winds, we hugged the windward side of the valley which was, as expected, very smooth and also gave us great groundspeed. I knew when we turned east and crossed the pass, we would be hit, so I slowed down, extended the gear, warned my wife, and we both tightened out seatbelts. Sure enough, as soon as we were on the lee side, kaboom, fortunately short lived and though we had moderate turbulence the rest of the way home.

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