radar wind profiles (VWP / VAD wind profile)

[Ronnie Bradley]

Hi all,
I have a question about reading wind profliles (speaking about stormlabs's VAD wind profile or GRLevel3's VWD). I know how to read the wind barbs and know that the long barbs = 10 kts and the smaller ones are 5 kts (flags are 50kts) and know the direction of the wind that they are pointing from. But what is confusing me is the colours used on the barbs. When I see, for example, a 20 kts wind barb in green, and one in yellow, or some other colour, how do I interpret the barb?
I read somewhere that the yellows and red's on the barb indicate higher winds but if I see a yellow 10 kts barb and a green 10 kts barb, how do I interpret the information?

 

[David Drummond]

The colors indicate how reliable the data is. The higher the number, the less reliable it is.

 

[Jeff Snyder]

VAD is not the same thing as VWP... VAD is an acronym for "Velocity Azimuth Display", while VWP stands for "Vertical Wind Profile" (which is what you are referring to). The colors on the VWP graphic represent the RMS values... I'd explain it with my own words, but the text copied below does a pretty good job of explaining VAD and VWP ...

From a Radar lecture from Dr. Mike Biggerstaff --> http://derecho.metr.ou.edu/~mikeb/radar/lab6.html

Another useful product that is based on the velocity is the Velocity Azimuth Display. We will discuss the theory behind this product in a future lecture. For now, let's just consider what the velocity field would look like for a uniform westerly wind blowing across the region sampled by our radar. Looking to the north, we would get zero radial velocity since the wind direction would be perpendicular to the orientation of the radar beam. Looking to the east, we would get the maximum receding flow. As we scanned toward south, the radial velocity would again decrease to zero. From south to west, the radial velocity would increase to a maximum inbound pointing due west. From west to north, the velocity values would decrease back to zero.

Now, if we considered a particular range circle centered on the radar and plotted the value of the velocity as a function of azimuth, we would get a perfect sine wave. This type of figure is a Velocity Azimuth Display (VAD). The best fit sine wave through a set of velocity values displayed in this manner will give the best estimate of the mean wind over the region between the radar and the range ring chosen for the VAD. The closer the velocity values are to the best fit sine wave, the more meaningful the mean wind estimate. The reliability of the mean wind estimate is usually stated in terms of the root-mean-square (RMS) of the distances between the sine wave and the data points along the velocity (y) axis.

Since a radar beam gains altitude with range, one can construct a vertical profile of mean wind estimates by using rings at different ranges or by using the same range, but higher elevation PPIs. This is done to create the Vertical Wind Profile (VWP) product. The colors used to plot the wind profile indicate the RMS value of the mean wind estimate. Since the WSR-88D collects data every 5 or 6 minutes in precipitation mode, a time series of vertical wind profiles can be created. This type of information can be used to help indentify wind shear changes in the environment of storms or the strength of the low-level jet.

 

[Ronnie Bradley]

Thank you all for answering my question .
So I gather that the green barbs are reliable; yellow is somewhat reliable; and red is rather unreliable.
I did come across a VWD screenshot on one of the links posted in this thread and the colours are mapped to RMS values and in that pic, the red had the highest RMS with a value of 16 whilst the black had a value of 2 and green was given a value of 0 (lowest).