I used the term "reported ceiling" without really thinking about it ceiling before. But the reg doesn't say that. 91.155, when talking about operating below the ceiling, does not use the word "reported." Just like it does with cloud clearances in general. And in contrast to visibility where the regs use the words "flight" and "ground" and some Part 135 and 121 approach rules, which use the phrase "reported ceiling."
OTOH, way back in 1975 and 1980, the Chief Counsel's office very clearly said, "The established and continuing legal opinion at this office is that the reported ceiling at the primary airport in a control zone governs as to whether VFR operations may be conducted
within that particular control zone." Whether it is still valid, I don't know, but since it is not in the public online collection:
MAY 21, 1979
AGC-23
Control Zone Weather
Chief, Airspace, Air Traffic and Environmental Quality Branch, AGC-23
AAT-300
This is in response to your memo of March 23, 1979, in which you ask for guidance on the question of what weather applies when more than one station is reporting the weather within a given control zone.
There has been considerable interest over the past few years within the FAA regarding control zone VFR requirements and the extent to which reported weather should be used to determine whether VFR operation within an entire control zone should or should not be conducted. At one point, a change was even proposed to Sec. 91.105(c) which would take into consideration the possibility of varying weather in a control zone. This proposal was eventually dropped, however, because of the safety implications and the enforceability problems which it raised.
The continuing legal opinion of this office is that the reported ceiling at the primary airport in a control zone (i.e. the airport upon which the designation of the control zone is based) governs as to whether VFR operations can be conducted within that particular control zone.
Even though there may be more than one weather station within a control zone, there will not be more than one at a given airport. If one of the stations is located at the primary airport, which will generally be the case, the report of that station governs. If neither of the stations is located at the primary airport (an unlikely possibility), the station used by the primary airport to determine its weather governs. This provides an enforceable precise basis for determining whether Sec. 91.105(c) has been violated.
This opinion linking "reported" ceiling to the "primary airport" in Sec. 91.105(c) has been the position of the office of the Chief Counsel for over 28 years.
No replacement concept has been proposed which has been shown to provide the same degree of safety and enforceability.
If there are airports or control zones which present special problems that are not fairly treated by this longstanding interpretation, these might be addressed on an individual basis in Part 93.
Let us know if we can provide further assistance in this matter.
There are also a few NTSB cases that take this view, but they are also pretty old. Whether or not things have changed, I don't know.
It would be very interesting to see what that LOA says.