How do meteorologists determine how tall a thunderstorm top is?

Question

I am a pilot, and of course check the weather before departure. On the weather resource I use to look at convective activity, for each thunderstorm, it says it's direction, speed, wether or not there is hail, rotation, or a tornado, as well as the height of the top of the thunderstorm.

Since radars only scan fairly close to the ground, how is the height of the thunderstorm determined? It is usually shown to the nearest 500 foot level. It shows the top of the storm anywhere from about 15,000 (150) to as high as 65,000 (650).

Answer 1

Each sweep of the radar changes its tilt, so they consecutively scan different angular elevations. The angular elevation along with the range data give the top--but only to the highest reflector.  The storm top may go higher, but if there are no reflectors the radar won't be able to tell.

Answer 2

Some radars now, including 1 that they have on our channel 5 news is able to calculate the height because they have a tool that uses lines to determine the tops of thunderstorm. It tips the radar to a vertical range to do this. For example, the first line is about 20,000 feet. Second is 30,000, and so on. The radar tilts the reflectivity, or the colors of the intensity, and see how many lines up it goes. So if the relectivity got to the 3rd line, then the storm would be about 40,000 feet up. This model is also a good indicator for hail as well, so that if the higher reflectivity colors, such as purple, makes it up to a high level, it usually indicates hail. Does all this make sense? Hope this answers your question.

Answer 3

Radar can be used to vertically scan a particular thundercloud(keeping the azimuth constant in the directon of the thunder cloud) and the height can be obtained.

Answer 4

I am also a pilot but only VFR so anything above FL 100 is out of reach for me and not interesting.

But I have sailed all my life, my father was a military pilot, teaching meteorology to aviators and ... I also teach meteorology to PPL-A students.

My understanding is that when a thunderstorm forms as a towering cumulus from a cumulonimbus, it goes all the way to the tropopause, also FL 340 or somewhere there.

True, big airplanes have a weather radar and sometimes fly over it but ... I don't think meteorologists give any information as to what the 'top' is. As I understand, the top is the 'anvil and mostly ice clouds.

One thing is for sure; when I read TS or even CB on the TAF, I don't fly. Or, I fly very carefully, giving those CB cells a wide berth, to put it in a sailor's mouth.

Answer 5

The graphic you linked to on this question is an estimated "Storm Max Tops" graphic added to the current radar picture.  

The computer collects the highest max tops estimated from each radar sweep, then plots those tops  that they think will be important for pilots.  These are really estimates based on the collected data for each set of cells or areas of reflectivity returns. It is important to know that this estimated data.  Sometimes, you can get a better idea from the FAA pilot reports.  Tops are also sometimes placed into the aviation and fire weather forecast.  

As you have noted, the height is capped.  This graphic is based on the estimated cloud tops from a network of radar data.  Unless the radar is located on an elevated base like on the top of an mountain, the beam of the radar are always pointed at an angle of at least 0.5 degrees to the horizon at the lowest scan.  After the lowest scan is made, depending on what mode it is set on, it will continue to take additional scans at higher and higher angles.  

Since almost all scans are are pointed upwards to some degree, the more distant the storm cell is from the radar, the higher in elevation the beam can collect data from the storm cell.  However, there are limitations as to how far a storm cell is and what kind of data we can collect.  

Once a complete set of scans are made, the computer can then put a 3-D picture together of most of the nearby storms.  We can combined all the data collected and display the data in many ways.  We can get a good estimate of a nearby storm from this data set plotted on the vertical plane.  For details...see the following links...

http://www.nws.noaa.gov/mdl/fsi/index.ht...

http://www.srh.noaa.gov/abq/feature/JM_X...

Example of a "slice" from a storm plotted on the vertical plane...

http://www.wbuf.noaa.gov/jl1897img.htm

One other factor...the Earth's surface is curved.  So a beam pointing the the horizontal direction will be higher in elevation to the Earth's ground surface as it moves away from the radar.  So even if we did not angle the beam 0.5 degrees or higher, out pulse radar beam will still sample a higher elevation as the distance increased from the radar.

Hope this helps you picture what the current radar system can do.