[CT Birds] Active Radar (& some instructions)

Roy Harvey rmharvey at snet.net
Tue Apr 20 23:44:10 EDT 2010

I just took a peek at the radar and there is some activity tonight for the first time in some days.  Nothing earth shaking, but good.

The link for the radar is http://www.rap.ucar.edu/weather/radar/.

Since a report like this often results in a question or two about what to look for, I have tried below to give a bit of information to get someone started who wants to do this for themselves.

NOTE THAT THE LINKS PROVIDED BELOW WILL ONLY WORK FOR A DAY OR TWO!  If you want to refer back to the images later you will need to save the pictures yourself.

Start at http://www.rap.ucar.edu/weather/radar/
On the left choose "Regional reflectivity".
On the right leave it at "Single image" until you know your way around.

On the right, when you have to specify the date and time, you MUST take into account that this uses GMT (Greenwich Mean Time) not EDT (Eastern Daylight Time).  GMT is also known as UTC (Coordinated Universal Time), which is what it is called on the radar maps.  Our EDT is four hours behind, so when I look at the radar at 11PM our time it says 0300 UTC with tomorrow's date.

With those choices made it is time to click on the map.  You can click on the words "Contiguous U.S." at the top of the map and see the entire country, or you can click on a specific spot within the U.S.  To see our area I click on the radar site on Long Island.

Look at the radar regularly so that you know what rain and snow and storms look like.  As of 11PM you can find them down in Georgia, Northern Oregon, north-east Nevada.  See:

So that is what heavy weather looks like.  Now lets look at what birds look like.  The first is around here, the second down in Texas where things are much busier.

If you compare the first group with the second you will see that the weather looks comparatively solid, while the birds look speckled.  Also note that birds are shown centered around each radar, sort of like a donut.  Weather does not show this donut shape, though there can be artifacts of the way it scans.

So it comes down to speckles and donuts.

It is also possible to get some idea of the direction the birds are moving.  Tonight's image is not as clear as I would like but lets try it anyway.  On the left change to the "0.5° Velocity" option, and then click on the radar point (+ sign) on Long Island.  Right now it looks like this:
This only works toward the more central part of the circle.  It measures how much the birds (or weather) is moving toward or away from the radar.  Look for the gray areas that match to zero on the scale.  In those areas - due west in the image I linked to - the birds are not moving toward or away from the radar at the center of the circle, they are moving tangentially (northbound).  As we go up the scale the motion is away from the radar site on Long Island, as we go down the scale they are moving toward the radar.  The image appears to show motion toward the north-east, where the colors are strongest from the top of the scale.

Note that the "0.5° Velocity" option pretty much ignores how heavy the concentration of birds is.  In the examples I linked to the regular image did not show much activity to the NE of the radar, but the velocity showed strong colors for motion in that direction.  So there are fewer birds, but they are moving directly to the NE at a pretty good clip.

The final option I want to discuss is the "Loop duration" option on the right.  This is very slow to use, and I have had problems when I asked for more than a few hours.  Also note that the date and time are for the END, so if you ask for three hours it will be the three hours before the time specified.  I have also found that this option doesn't work on every computer, and I have no clue why.  However if it does work it can show another important aspect of what makes birds look different from the weather by showing the "lift off" as it gets dark.  Rather than use the duration, here are a few single images from tonight to give you the idea.  There is an hour between each one.

You can see how the radar went from clear to busy to busier in just two hours.  Weather doesn't work like that, it moves across the map rather than just appearing suddenly.

Have fun!

Roy Harvey
Beacon Falls, CT

More information about the CTBirds mailing list