What is the Yellow Dashed Line?

Apr 10, 2008
59
16
11
29
Lexington, MA
isaac.zpato.net
Looking at the sounding, I believe that:

The yellow dashed line is the surface based lifted parcel.
The white dashed line is the (edit) most unstable lifted parcel.

Both use virtual temperature.

More details are here:

Sharppy supports selecting additional parcel traces by right-clicking the sounding. I believe you can do the same on weather.cod.edu
 
Apr 10, 2008
59
16
11
29
Lexington, MA
isaac.zpato.net
Very good question.

The surface based lifted parcel is calculated using the virtual temperature, which is a function of temperature and moisture. Because water vapor is less dense than air, the virtual temperature is always a couple of degrees warmer than the actual temperature for warm/humid conditions.

Depending on the user settings, Sharppy also displays the environmental virtual temperature as a dashed red line.

CAPE is the area between the virtual temperature and the parcel trace. You'll notice that as moisture decreases with height, virtual temperature approaches the actual temperature.

Importantly, this means that there is a little bit of CINH for the surface parcel below. If the virtual temperature line is removed from the sounding, it gives the misleading impression that the atmosphere is entirely uncapped.
17787
 

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Mike Z

EF1
Sep 11, 2017
60
32
11
Northeast USA
www.undertheanvil.com
Looking at the sounding, I believe that:

The yellow dashed line is the surface based lifted parcel.
The white dashed line is the (edit) most unstable lifted parcel.

Both use virtual temperature.

More details are here:

Sharppy supports selecting additional parcel traces by right-clicking the sounding. I believe you can do the same on weather.cod.edu
Thanks. The satellite and radar section on weather.cod.edu is an amazing place to look at live data. I found it yesterday from a Reddit post.
 
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Aaron Dawes

Enthusiast
Aug 11, 2019
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Bethany, Oklahoma
Very good question.

The surface based lifted parcel is calculated using the virtual temperature, which is a function of temperature and moisture. Because water vapor is less dense than air, the virtual temperature is always a couple of degrees warmer than the actual temperature for warm/humid conditions.

Depending on the user settings, Sharppy also displays the environmental virtual temperature as a dashed red line.

CAPE is the area between the virtual temperature and the parcel trace. You'll notice that as moisture decreases with height, virtual temperature approaches the actual temperature.

Importantly, this means that there is a little bit of CINH for the surface parcel below. If the virtual temperature line is removed from the sounding, it gives the misleading impression that the atmosphere is entirely uncapped.
View attachment 17787
Why does less density from moisture increase the virtual temp? I've been trying to research this for hours and cannot find any answer at all. I'm sure it's obvious, but it's possible i forgot how it works.
 

Jeff Duda

Resident meteorological expert
Staff member
Oct 7, 2008
3,044
1,573
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Westminster, CO
www.meteor.iastate.edu
Why does less density from moisture increase the virtual temp? I've been trying to research this for hours and cannot find any answer at all. I'm sure it's obvious, but it's possible i forgot how it works.
The chemical substance H2O has a lower molecular mass than does the standard constituency of "dry air," so adding water vapor to dry air at constant temperature reduces its density.

A parcel's virtual temperature is the temperature it would have to have in order to have BOTH zero water vapor AND the same density as the parcel's actual density. Since heating air will reduce its density, then it follows that adding moisture to a parcel is equivalent to increasing its virtual temperature.