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EZTip No. 35 - Why the Skew-T?

Updated: Jun 5, 2023

There’s no doubt that the Skew-T log (p) diagram is not for every pilot. That’s fine. It takes a concerted amount of time and effort to learn and even more time to master. In the end, most pilots just don’t want to dedicate the time and to learn how to unlock its plentiful secrets. But there are several reasons to make that time and make that effort since it provides weather data in a way that is unlike any other tool you will use and forces you to really understand the basic concepts of weather. Yes, it may look “arcane” to some pilots and other pilots opine that it’s like using a sextant to navigate. Hardly so, but that’s simply because it has a very specific use…to drill down to learn more about how the atmosphere is poised and to help quantify uncertainty. In other words, it provides remarkable clarity to a situation that may be difficult to decipher on the typical weather guidance pilots rely on.

Yes, you can find some of the same information plotted on the EZWxBrief route profile and meteogram. Those two views show you the potential of icing and turbulence and you can see the temperature and wind plotted vertically. To top it all off, both will show the altitude where clouds may exist or where the sky may be clear. Full stop, right? Who needs the Skew-T?

When flying any piston-powered airplane, why should you care about learning more about managing your engine. After all, the “book” gives the settings for the throttle and mixture. Full stop, right? Not exactly. Any pilot that has gone through a detailed engine management course knows there are many reasons to dig deeper. There’s not only a financial component to proper engine management, but there’s also a safety component. The goal of such education is not to teach you to become an A&P, but to extend your superficial knowledge to make better decisions that have a real payoff in the end. So why should weather be any different?

Weather is the single biggest physical factor that limits your flying activity. Not unlike engine management, digging deeper into the basic principles of weather has a significant payoff as well. It may not have a huge financial impact (that’s likely why pilots don’t see advanced weather training as essential), but it will have a significant payoff to some pilots when it comes to making preflight decisions to stay or go. But you can count on it; every time there’s an accident where challenging weather existed, the Internet forums light up from the astute pilot community, “what did the Skew-T look like.” It is that important.

First, let’s talk about the educational component. To master the Skew-T diagram, you must learn more about the basic nuts and bolts of weather. Not a bad thing for any pilot that does more than just the occasional circuits in the traffic pattern. The goal is not to teach you to become a budding meteorologist, but to extend your knowledge well beyond the basics you were taught during primary training. Even if you don’t ever use the Skew-T, it will challenge your most basic understanding of weather. Consequently, learning how to read the Skew-T can be a canvas to learn important weather concepts to include what causes turbulence, airframe icing and thunderstorms just to name a few. If you don’t want that kind of knowledge, then the Skew-T is not for you.

Second, let’s look at what the Skew-T provides. While the route profile in EZWxBrief or any of the heavyweight apps will provide some useful information, it will never give you the details needed to diagnose some aspects of weather. For example, can you determine if trapped lee waves will be likely using a vertical route profile? Not likely. With a click or two and some basic knowledge of the trapped lee wave signature on a Skew-T, you can quickly make this determination. Why is this important? This won’t affect pilots flying at FL300, but knowing you might experience a downwash when traversing low and slow through a mountainous area is quite important and helps to alleviate any surprises you may have.

What about the potential for microbursts? These often occur with benign-appearing, low-topped convection in the presence of very dry conditions below the cloud bases or what is called the lifted condensation level. Once again, this is hard to visualize on a vertical route profile or from other weather guidance like the prog charts or TAFs, but comes through loud and clear on a Skew-T diagram if you know what to look for.

One last's common to hear pilots suggest that somehow the Skew-T is the source for some of the route profile views you may find, such as the one from EZWxBrief. Just to be clear, the Skew-T is just a visualization tool so that you can see the vertical profile of temperature, dewpoint temperature and wind as a function of pressure or altitude at a single point using a radiosonde observation or model forecast. In other words, it's a way to plot data from those two sources. The way in which the Skew-T is constructed allows you to determine many parameters that are not easy to visualize on a route profile such as seeing the lapse rate just how the atmosphere is poised from a convective standpoint.

If you want to learn more about weather and how to interpret the Skew-T log (p) diagram, you can order your copy of The Skew-T log (p) and Me: A Primer for Pilots that is available in both softcover and eBook format.

Most pilots are weatherwise, but some are otherwise™

Dr. Scott Dennstaedt

Weather Systems Engineer

Founder, EZWxBrief™

CFI & former NWS meteorologist

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