×
PPL Video Lectures (10 Jul 2020)

PPL Video Lectures covering Aerodynamics, General Knowledge, Performance, Meteorology And Navigation are now available through our website see front page for details.

× Welcome to the CPL Meteorology question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

How do we calculate cloud base?

• Edlina kalfabun
• Topic Author

Edlina kalfabun created the topic: How do we calculate cloud base?

How do we calculate cloud base?

Please Log in or Create an account to join the conversation.

• Posts: 2155
• Thank you received: 171

bobtait replied the topic: How do we calculate cloud base?

I'm not sure exactly what you want with this question. The pilot never needs to 'calculate' the cloud base, the Met man does that. If you mean how is the cloud base expressed, it depends on the forecast you're reading. A Graphical Area Forecast gives cloud base above sea-level and an aerodrome forecast (TAF) or (TTF), gives cloud base above ground level.

See also AIP GEN 3.5 para 3.7.1

Please Log in or Create an account to join the conversation.

• Posts: 168
• Thank you received: 29

Carello replied the topic: How do we calculate cloud base?

You can calculate the convective cloud base if you know the surface temp and dewpoint temperature.

Cloud Base in feet = (Air temperature at surface – dew point temperature at surface) x 400'

The calculated base will be the height above the surface observation.

If you grab an F160 you should be able to derive this formula for yourself.
The following user(s) said Thank You: CameronD

Please Log in or Create an account to join the conversation.

• Posts: 4
• Thank you received: 3

flyingmeatball666@gmail.com replied the topic: How do we calculate cloud base?

Cloud base AGL

(Temp - dew point ) / 2.5 x 1000

Please Log in or Create an account to join the conversation.

• Posts: 35
• Thank you received: 0

adambernhardt replied the topic: How do we calculate cloud base?

word is its sneaking into the exams

Please Log in or Create an account to join the conversation.

• Posts: 2155
• Thank you received: 171

bobtait replied the topic: How do we calculate cloud base?

Rising unsaturated air cools at about 3° per thousand feet and dew point temperature lapses at about 0.5° per thousand feet. So the difference between the rising air's temperature and dew point temperature reduces by about 2.5° per thousand feet of ascent.

So the approximate height of the cloud base above ground level can be calculated as:-

Cloud base in thousands of feet = (Surface air temperature - Surface dew point temperature) ÷ 2.5

For example, if the surface air temperature was 18°C and the surface dew point temperature was 6°C, the cloud base would be approximately 4800 feet.

Please Log in or Create an account to join the conversation.

Time to create page: 0.194 seconds