WX Radar Rules of Thumb
 

I know I have seen it before somewhere, but can't recall where. Can anyone tell me some of the rules of thumb equations for calculating the height of precipitation in a thunderstorm from the wx radar? For instance, painting a cell at 50 miles, and utilizing the tilt to find out how high the precipitation reaches?

Thanks.

Forget it. If you are even thinking about climbing over it, and you think you may not be able to, then GO ROUND IT, giving it plenty of room; if you can't do that, then turn back. Sorry if I haven't been very helpful in answering your question but don't ever mess with thunderstorms.

Hello,

Maybe you mean that 1° corresponds to 1 NM at a range of 60 NM. Working with proportions you can find out values for different ranges. Is that what you were looking for ?

I have seen a formula where using the aircraft's altitude, distance from thunderstorm based on the weather radar and the degree's of tilt, you could actually work out the approximate height of the cell. I myself would like to know this formula, but for the life of me I cannot remember where I saw it.

Simple one-in-sixty rule. If you are at high level say FL350,tilt the radar down to -1, the waht you see at a 30nm range is half a nm below,that is 3000ft below you. Work like magic. Try tilt the radar all the way down to -8 or -9 then "walk" it upwardwards and note what shown on every 1 degree up. This way you can paint a very clear picture of shape of the cell ahead and work together with the freezing level,wha-la! The storm is naked!!!!

Hi,
This is out of a met book and hope it'll help :

(tilt angle - half beam width ) x 100 x range in NM = approximate height difference of cloud's top(in feet) from your flight level .

It works pretty nicely .

I...

Try this:

Height of cloud tops relative to the aircraft=

Range in feet x (weather radar scanner tilt - 1/2 beam width)
------------------------------------------------------------
60

e.g a cloud 50 miles away,tilt 1 deg up ,beam width 4 degrees:

50x6080x (1-2)
-------------- = 5067 ft
60

Hope it helps, but gotta agree with smudger..give them plenty of space

Cheers
Camel:)

Avoiding TS by climbing is for the hard of thinking only.

They also grow rapidly. So by the time you reach the cell, it might be well above you. The 'rule of thumb' is thus of limited practical use.

So I concur, give them a wide berth.

Company gave us a booklet with radar tips. Had the formula in it. Cool, a way to finally figure out how high the tops are.

Coming back from Europe across Canada. Storm ahead. We both start playing with the radar. "How high did you figure?" Both within about 2000' of each other.

Then we fly by the storm. It's way above us.

Booklet goes in the trash...

The idea is to find the height of the precipitation so you can estimate its likelyhood of being a thunderstorm as opposed to a bit of rain.

Aerocat. you haven't flown in the tropics much have you?

I have a little, why do you ask?

What exactly is the beam width again? I remember reading about it but I cant seem to remember right now.

The best lesson for thundestorms is to understand their life cycle well. Usually not possible to climb over them but easier to avoid laterally.

Aerocat
You do what you like.:rolleyes:
I've been IN one or two and above a few. I suggest you do what most folk do which is avoid them laterally, even if it means a bit off off track nav.

If you'd rather overfly them, fill yer boots!:)

Where have I suggested flying over one?

Like I say, the idea is to assess whether it is a thunderstorm or some other type of rain cloud. If it has high vertical development then it is probably a TS or going to become one, so you go around. If it is only up to 10,000 feet or something then its just heavy rain and you can fly through it. Obviously there are other indicators like the steepness of the contour, irregular shapes and so on. This is all supposing that you can't see it because it is embedded or night time or something.

There are better ways of determining intensity. Don't know if wx radar on your type can show contours/ colours or not. This gives a good idea of whats inside as does the shape of the return.
You'll soon learn anyway!:ok:

The tropics do not cover the entire world! :)

When flying at night in the central United States, particularily during the summer months, it is not at all uncommon to have dissipating lines of thunderstorms which contain sections that top out well below normal jet cruising levels. The capability to judge the height of these storms greatly enhances situational awareness and the ability to choose the most sensible route across the line. Since some of these lines may literally stretch from Texas to Iowa, (several hundred miles) determining a low spot will often be one of the strategies employed to decide the best location to cross. It is sometimes not possible to cross in a location where NO precipitation returns are present on the wx RADAR.

Using the tilt to determine the areas of highest and lowest height of returns is one of the actions which may be performed in determining the most and least favorable places to cross the line. This can be a good confirmation of what is indicated by other information sources.

The specific techniques used will vary according to the particular characteristics and specifications of the installed system but the following general technique works well to further verify suspected "low' or "soft" spots in the storm line in the aircraft I fly. Remember, this information is best used along with all other available information, not by itself.

With the range set to 100 miles, note the location of precipitation returns of interest, then tilt the antenna down until ground returns are noted at the 60 mile range. Note the selected angle. Now tilt the antenna up until the precipitation returns in your selected "soft spot" disappear from the screen. Note the tilt angle selected and find the difference between the two angles. Each degree of tilt equals aproximately 1 mile of height above the ground at 60 miles, so if it took 5 degrees of tilt difference to make the returns disappear, the precipitation tops are at aproximately 30,000' above the ground if they are at 60 miles. Adjust the tops estimate by 1,000' for each 10 miles of range difference from 60 miles. Higher if closer, and lower if further.

Look, this isn't anything more than a second, third or fourth way to verify what you think is happening ahead. I would never rely on this method as a sole source of information to make a decision as to where a storm line will be crossed. Precipitation returns by azimuth and intensity, lightning detection, reports from preceeding traffic, ATC RADAR reports and route suggestions, downlinked doppler RADAR feeds, and yes, good old visual observation and assessment are all arrows in the quiver. The more of these tools you have, the better. Each can be used in conjunction with the others as an aid in deciding the most appropriate course of action to take in crossing a line of storms which cannot be entirely circumnavigated. It's done all summer here, many thousands of times. I find the antenna tilt function to be one of several tools which can be used as an aid in enhancing situational awareness. Please remember that cumiluform cloud tops may extend well above airborn wx RADAR precipitation returns. Never rely soley on these precipitation top estimates to determine a course of action.

Best regards,

Westhawk

You mean like the contours and shapes I mentioned in my post just above yours? Yeah I guess I'll learn all about that soon enough :hmm:.