Building clouds have always
waited for me from April through September. Until now, I have
never
seen the insides of a green or black cloud.
Don't fly through clouds that are either black or light green. And please, creep carefully through the white, benign variety. Green clouds get their color because light refracts through ice. Black ones get that way because water droplets stop light.
Where do you find green clouds? In the upper third of cumulonimbus monsters. Leave aside the question of why you were there in the first place. That light green ice inside clouds is called hail.
Where does hail begin? What follows is empirical and subjective. I have not yet found it in textbooks. Someone reading this account will undoubtedly prove it true. Until now I have not figured out how to collect the physical evidence and survive.
Having flown the classes of airplanes in Table One, all the numbers apply to me, except the nautical-miles-per-minute. They are from airplane handbooks.
Building clouds have always
waited for me from April through September. Until now, I have
never
seen the insides of a green or black cloud.
As the nice white, friendly-looking cumulus clouds are building, their tops have reached the freezing level. When that happens, they go ballistic and attain two-thousand feet per minute upward mobility.
A small halo of freeze-dried moisture appears as a gossamer veil atop the building cumulus the instant it punches through the freezing level. The veil is soon swallowed by the rapidly rising cloud. Look quickly or you'll miss it. Keep scanning along the freezing level and you'll find more of them. It happens to every cloud that dares rise that high in life.
How do you find the freezing level? Look at the Outside Air Temperature gauge. The inside ring is notched in two-degrees-Centigrade increments. Say it is three notches warmer than zero-degrees Centigrade. Your view should be directed at an altitude three thousand feet above you. And remember, if you try to wade through clouds with tops above the freezing level, advise everyone to fasten seat belts, please.
Where is the freezing level? On a Standard Day you should keep an eye on the outside air temperature as you're climbing above seven thousand feet. The definition of a Standard Day is by common agreement among nations. Sea level is plus-fifteen degrees Centigrade.
An American pilot's skin sensors are set for Fahrenheit. For them being in shirtsleeves a 32 deg. F. is miserable. Fifteen degrees of Centigrade will, therefore, feel like a balmy fifty-eight degrees Fahrenheit to an American.
Zero degrees Centigrade is found around seven thousand feet and above. The gossamer veil is seen being absorbed by the building cumulus. Look sharp because it will be swallowed quickly. Where do these ice crystals go? They go straight up, acting as magnets for more moisture.
Above thirty thousand feet those innocent crystals are big enough to refract light. Stay far away. Escape from this region of wondrous beauty.
Why concern yourself with this gossamer veil clue? Depending on the class of airplane and level of your experience, you may need to pick your way through buildups. See TABLE ONE below
| TABLE ONE | |||
|---|---|---|---|
| Cruising Altitude | N.M. per minute | Pilot hours | |
| Small Single-Engine | 5,000 | 2 | 500 |
| Large Single-Engine | 10,000 | 3 | 1000 |
| Unpressurized Twin | 15,000 | 3 | 1500 |
| Pressurized Twin | 20,000 | 3 | 1500 |
| Turboprop | 30,000 | 4 | 3000 |
| Jet | 40,000 | 5-7 | 5000 |
I have used a knots-per-minute speed reference. This is to emphasize how quickly the clouds build. By the time you get there, the gate is closed.
In Figure One, you are ten miles from the building cumulus clouds, flying at five thousand feet in a large single-engine or unpressurized twin. When you arrive, the clouds will look like Figure Three.
Avoid the ice crystals lurking inside those clouds. They are wafting upward with great mobility, getting bigger, big enough to be called hail. It will harm windshields and make dents in airplanes.
If you were in a pressurized airplane, you wouldn't be cruising between buildups. You would see them, however, as you climbed and descended.
It comes to mind that some readers will notice these are daytime descriptions. At night you'll be notified by lightening flashes. Hardly anyone is brave enough to aim directly at it.
The clues in this story makes your weather radar more
meaningful. Enjoy the ride.
RETURN TO MAIN PAGE