I'm working on a Python script that takes in metar data and decides if an airport is VFR/IFR/MVFR etc. This is the website that I'm getting the info from:


I'm using this website to decide if an airport is IFR/VFR. I understand the visibility requirements, but not the ceiling. What if an airport is overcast at 500, broken at 5000, scattered at 3000? What takes priority to decide the ceiling requirement?


  • $\begingroup$ The lowest one does, however it also depends on the airspace designation of the airport for the actual requirements so I hope you are taking that into account. $\endgroup$
    – Ron Beyer
    Oct 3 '19 at 17:02
  • $\begingroup$ @RonBeyer Thanks for the reply, so the ceiling requirements are different for class B,G,C,D airspace? Sorry, but I don't see that in the link. Where can I get that info? $\endgroup$
    – Matt Damoz
    Oct 3 '19 at 17:11
  • $\begingroup$ Here is a good reference, for Class B you have to remain clear of the clouds (don't touch them), for Class G it's the same, unless you are 1200 feet AGL or less (see note on bottom). $\endgroup$
    – Ron Beyer
    Oct 3 '19 at 17:18
  • $\begingroup$ @RonBeyer Thanks, this will help me with my if statements. I'm a commercial pilot, but I'm in IT, and I code for fun. My plan is to create a map of all the ~1500 airports in the US with color codes. $\endgroup$
    – Matt Damoz
    Oct 3 '19 at 17:21
  • $\begingroup$ Geez I must be getting rusty-- forgot that "clear of clouds" in Class G was only valid for daytime operations below 1200' agl. Not that there are many places where Class G extends above 1200' agl anyway... $\endgroup$ Oct 3 '19 at 17:59

There are many websites and apps that do this for you already. The website SkyVector will show colored dots that indicate what the airport status is. There is also a ForeFlight app that will show colored dots on their maps. I am not endorsing any products, simply pointing out tools that accomplish what you are asking.

All these companies use information found in AC 00-45H. I added color for clarification.

Description of aviation airport weather

Personally, I would stay away from getting into the details of what class airspace an airport is currently using. Although, the information can be easily found, it may be a challenge to code successfully. The airspace above an airport can also change depending on whether an control tower is in use, the day of time or other factors.

The other reason, is 91.155(c). Hence, any ceiling below 1,000 FT makes the airport IFR.

Except as provided in §91.157, no person may operate an aircraft beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when the ceiling is less than 1,000 feet.

To answer your other question. The ceiling is defined as the lowest BKN or OVC layer. In your example above, the ceiling is OVC 500.


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