Extreme turbulence and the Skew-T

[Scott Dennstaedt, PhD]

If you are not a Skew-T fanatic, you should be.  Here's an excellent example of what the Skew-T can do for you.  Take a look at this Skew-T analysis from 15Z in southeastern NC.  

Notice at about 6,500 ft MSL, the winds are from the southeast at 58 knots and then around 9,300 feet, they are from the southwest at 57 knots.  This is an excellent example of directional shear in the wind aloft.  The key though is the moist unstable layer that starts just below 8,000 feet that enables the air to mix.  All of this coupled together is the reason this pilot reported extreme turbulence at 8,000 feet MSL.

If you are not a Skew-T fanatic, make a New Year's resolution to become one!

  

[Jeff_S]

Scott, what about those lines indicate instability? I get that the air is moist since temp and dew point are the same, and I know how to interpret the wind shear flags. But why do the temp lines indicate instability?

[Scott Dennstaedt, PhD]

13 minutes ago, Jeff_S said:

Scott, what about those lines indicate instability? I get that the air is moist since temp and dew point are the same, and I know how to interpret the wind shear flags. But why do the temp lines indicate instability?

Jeff,

Instability is all about lapse rate.  Large lapse rates means unstable air.  Notice that the lapse rate beginning at 8K nearly follows the moist adiabatic lapse rate.  That's the largest lapse rate Mother Nature can dish out in saturated conditions.  You can find this article I wrote in IFR magazine many years ago that discusses lapse rates that should help.  

[Raptor05121]

Would a Skew-T chart be a +1 to mention on an IFR checkride as an additional weather report for flight planning purposes?

[Jeff_S]

8 hours ago, scottd said:

Jeff,

Instability is all about lapse rate.  Large lapse rates means unstable air.  Notice that the lapse rate beginning at 8K nearly follows the moist adiabatic lapse rate.  That's the largest lapse rate Mother Nature can dish out in saturated conditions.  You can find this article I wrote in IFR magazine many years ago that discusses lapse rates that should help.  

Thanks Scott.  I had read that article many years ago but it was a good refresher. And yet I am still confused. In both your note here and the article, you say that when moist air approaches the DALR that marks instability. But as I interpret the chart in this topic, the point you indicate seems to show that the saturated air is following the MALR...that’s the brown line, right? So as I understand things, that would mean relative stability.  What am I missing? Why wouldn’t the extreme turbulence be due to wind shear at the boundary layer between the two air masses?

I appreciate your guidance...these posts are quite educational.

[Scott Dennstaedt, PhD]

8 hours ago, Raptor05121 said:

Would a Skew-T chart be a +1 to mention on an IFR checkride as an additional weather report for flight planning purposes?

Alex,

In my experience, unless you are doing your checkride for a glider rating, no, most DPEs don't even know about a Skew-T diagram.  Now, if they ask you, "How do you determine the freezing level along your proposed route?" you could say, "I use a Skew-T diagram to help make that determination."  Or if you are a WeatherSpork user, you could show the examiner the profile view that depicts the freezing level along your entire route (dotted blue line).  

 

[Scott Dennstaedt, PhD]

1 hour ago, Jeff_S said:

Thanks Scott.  I had read that article many years ago but it was a good refresher. And yet I am still confused. In both your note here and the article, you say that when moist air approaches the DALR that marks instability. But as I interpret the chart in this topic, the point you indicate seems to show that the saturated air is following the MALR...that’s the brown line, right? So as I understand things, that would mean relative stability.  What am I missing? Why wouldn’t the extreme turbulence be due to wind shear at the boundary layer between the two air masses?

I appreciate your guidance...these posts are quite educational.

Jeff,

Here's what I said...

"Notice that the lapse rate beginning at 8K nearly follows the moist adiabatic lapse rate."  That's the MALR, not DALR.  Yes, when the atmosphere is saturated (as it is here) and the environmental lapse rate is moist adiabatic (follows parallel to the MALR), then it's the most unstable as it will get.  Instability means there's a large change of temperature with height.  Yes, the curved "brown" line is the MALR reference line (see below).  In this case, the environmental lapse rate is at its greatest between 8K and about 10K.  The more the line leans to the left, the more unstable the atmosphere.  So there's a stable or nearly isothermal layer below this (below 8K).  

I've flown into an area like this before (through the Richmond, VA area) and it feels like you are driving a car fast over an endless road of speed humps.   

[bob865]

Wherea are you pulling your skew-t chart?  Your's looks different than the one I just pulled.  Specifically the winds.  I did a google search for skew-t to find this.  https://www.ospo.noaa.gov/Products/atmosphere/soundings/sfov/skewt/index.html                

 

[Scott Dennstaedt, PhD]

23 minutes ago, bob865 said:

Wherea are you pulling your skew-t chart?  Your's looks different than the one I just pulled.  Specifically the winds.  I did a google search for skew-t to find this.  https://www.ospo.noaa.gov/Products/atmosphere/soundings/sfov/skewt/index.html                

 

 

Bob,

I pulled the Skew-Ts out of my WeatherSpork app, but you can also get them from http://rucsoundings.noaa.gov.  The NOAA site has been operational since about 1997 or so.  The site you are using are satellite-based soundings from GOES.  

[mike_elliott]

10 hours ago, Raptor05121 said:

Would a Skew-T chart be a +1 to mention on an IFR checkride as an additional weather report for flight planning purposes?

Depends on the examiner if they like to be "snowed" or not. If you want to go down a rabbit hole, be prepared to fully explain their use, how to interpret, etc. Alex, might I suggest you stick to answering questions asked for the best results on the oral. The DE has a plan of work he/she will follow and that will cover the bases of weather briefing for your planned flight. They will be able to tell if you know what you are talking about or not without the need to acquire "points".

[mike_elliott]

1 hour ago, scottd said:

I pulled the Skew-Ts out of my WeatherSpork app

Why? seems like it and a laymans interpretation would be a valuable deliverable for your app.

[RLCarter]

18 minutes ago, mike_elliott said:

Why? seems like it and a laymans interpretation would be a valuable deliverable for your app.

I think he retrieved (pulled) them from his app

[mike_elliott]

5 minutes ago, RLCarter said:

I think he retrieved (pulled) them from his app

Ah...my bad...thanks!

 

[Danb]

Mike it looks like the rucsoundings from noaa, I’ve been studying with Scott’s site in near invaluable IMO, it’s the best wx system I’ve used to date, very much worth the yearly app fee.

[Scott Dennstaedt, PhD]

21 hours ago, mike_elliott said:

Ah...my bad...thanks!

 

That's correct Mike, I retrieved it from my app...sorry for my poor english...it ain't too good sometimes.