BWCA How to find the height of the base of clouds- especially convective ones. Boundary Waters Group Forum: WEATHER STUFF
Chat Rooms (0 Chatting)  |  Search  |   Login/Join
* For the benefit of the community, commercial posting is not allowed.
Boundary Waters Quetico Forum
   Group Forum: WEATHER STUFF
      How to find the height of the base of clouds- especially convective ones.     
 Forum Sponsor

Author

Text

07/28/2021 05:44PM  
In following up on the post on "high base thunderstorms" - I thought I would go into what "base" is and how to calculate quite accurately how high above ground they are.

"base" is the height of a cloud above ground level. In most cases we are talking about convective clouds (Thunderstorm clouds) but also rain clouds with no lightning usually works also but the formula is really for convective clouds.

The higher the base of your convective cloud, the less likely precipitation will make it all the way to the ground. Higher based clouds have higher bases because of dry air between the base and the surface. Precipitation that evaporates before hitting the ground is called virga and can be dangerous for small planes to fly through. The opposite is also true, lower based convective clouds have higher chance of their precip hitting the ground/ocean/surface.

So it makes sense that climates with higher amounts of water vapor will have higher chances of precip and thus wetter climates and vice versa.
Here is the formula for finding convective cloud bases-
TEMP (F) - DEW PT (F)
/
4.4
* 1000 = Cloud base in feet AGL (above ground level

So here is an example of a high humidity location such as Florida

Temp = 88F
Dew PT = 75F
88-75 = 13
13/4.4 = 2.95
2.95 * 1000 = 2950' or 3000'
3000' above ground level in this example would be base of convective clouds.

Example of drier location- such as the SW USA-

TEMP= 82F
Dew PT 48F
82-48= 34
34/4.4 = 7.7
7.7 * = 7700'
7700' above ground level in this example would be base of convective clouds

Doesn't take a rocket scientist to figure out which example has the greatest chance of the precip actually making it to the surface. But - the same elements of a Thunderstorm other than rainfall hitting the ground are usually accompanied by high base thunderstorms, ie-
lightning and high winds and even downbursts and microbursts.
Thanks for reading.

 
      Print Top Bottom Previous Next
07/28/2021 08:02PM  
Thanks for the refresher. I had learned this in flight school almost 30 years ago.
 
      Print Top Bottom Previous Next