It says “good picture” not “comprehensive picture”. And by that, they mean the pilot can build an understanding of the general weather conditions and surface weather pattern. If you were trying to literally draw a picture of the current and complete weather scene, which is what Flight Simulator aims to do, and what most of us are talking about here, then the METAR would be missing lots of information. Just to name a few as it relates to this thread:
- What types of clouds are over the field?
- What are the tops of those clouds?
- How fast and in which direction are they moving?
- Are the clouds growing or shrinking?
- Is there any high altitude cirrus?
The METAR might not give you any information about this. Sometimes it can, or sometimes it can be inferred, but lots of times it doesn’t say anything at all about these things.
And it’s only as current as the last update. Many of the METAR parameters are allowed to change quite a bit before an update is triggered.
Here are the federal requirements for issuing an update:
Which is why I said the ceiling could change by thousands of feet, the visibility by miles, and the winds by tens of degrees and still not qualify for a special METAR update.
It’s almost like the conditions that trigger a SPECI were designed to notify of significant impacts to aviation, not provide completely accurate weather reporting. 