Are Skew-Ts the source for the data on the EZWxBrief EZRoute Profile?

Updated: Oct 9, 2021


In a single word...NO! It seems quite common to hear pilots try to incorrectly compare a vertical route profile with a Skew-T log (p) Diagram. It's as they believe the Skew-T log (p) is some kind of primary source of data. For example, here's a common comment that shows a deep misunderstanding of the differences between the two when referring to a specific application's vertical route profile.


"I thought they used soundings as their base engine, but I guess not. I'd rather everything be based off of soundings."


There's a lot to unpack here. First, "soundings" are generated from two separate data sources. The first source is radiosonde data. Radiosondes (weather balloons) are launched twice daily at 11Z and 23Z throughout the world. The data collected from each radiosonde launch includes temperature, humidity (dewpoint), pressure and wind (speed and direction). The resulting data is called a radiosonde observation or RAOB. This data can be plotted as a function of altitude (pressure) on a thermodynamic diagram called a Skew-T log (p) Diagram. These are only available at locations where the radiosondes are launched as shown below.

Second, numerical weather prediction models produce output that is similar to the data collected by radiosondes, except that it's strictly a forecast (or analysis). These models write their data to a 3-dimentional grid. It is the gridded data that can be used to populate the Skew-T log (p) Diagram. Some online tools such as the one from NOAA (https://rucsoundings.noaa.gov) allow you to enter an airport identifier and the tool searches for the nearest grid point from the respective model (e.g., Rapid Refresh, Global Forecast System, etc.). Depending on the resolution of the model used, the grid point is typically within about 10 to 15 miles of the center of the airport's runway complex...often less.

Various applications such as EZWxBrief (https://ezwxbrief.com) provide a vertical route profile that makes use of the same model forecast data used to populate a Skew-T log (p) Diagram. However, data plotted on a vertical route profile isn't "from the soundings" as some pilots suggest...instead, the Skew-T is just a tool to plot some of the same forecast model data as is provided on a vertical route profile. Shown above, is the wind and temperature vertical profile found in EZWxBrief along a proposed route for a particular time of departure.

It's important to understand that this kind of depiction is different than what you get in a Skew-T log (p) Diagram. While forecast wind speed and direction at any segment point along the route is similar to the wind forecast depicted on the Skew-T log (p) Diagram, it is hard to see the actual lapse rates given that the Skew-T plots temperature vertically whereas a route profile plots it horizontally and has no reference lines to determine lapse rates. Also, you cannot "lift a parcel" of air on a vertical route profile to determine moist instability or derive other useful thermodynamic parameters such as CAPE. Therefore, it's still important to learn how to use the Skew-T log (p) Diagram given that it has other features that a vertical route profile cannot offer.


Moreover, a plot of clouds, icing and turbulence on a vertical route profile are based on some formula defined by the application or other forecast model data to determine the presence or absence of these elements. The Skew-T log (p) Diagram simply shows the "environment" for which these various elements may exist. These things can be determined from a Skew-T log (p) Diagram, but requires some basic interpretation.


Most pilots are weatherwise, but some are otherwise™


Dr. Scott Dennstaedt

Weather Systems Engineer

Founder, EZWxBrief™

CFI & former NWS meteorologist




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