Cannot parse where visibility is directional

[drmrbrewer]

According to this page:

Visibility can also be listed per direction. 1500SW 2000NE means the visibility to the southwest is 1500 meters and 2000 meters to the northeast.

It seems that this isn't accounted for by this parser... as per this example it gives the following error:

UnexpectedParseError: container.visibility not instantiated

[aeharding]

Based on the following, page 25-28, it appears as if the directional visibility will always accompany a primary visibility.

https://www.vaisala.com/sites/default/files/documents/Vaisala%20unmanned%20automatic%20weather%20observations%20at%20airports.pdf

The minimum visibility is also included when the visibility in one direction, which is not the prevailing visibility, is less than 1,500 meters or less than 50% of the prevailing visibility and less than 5000 meters. A direction is also added if possible, as N, NE, E, SE, S, SW, W and NW. If the direction cannot be determined like in AUTO metar, NDV (No directional visibility) keyword can be used.

It seems like a visibility with a direction attached will always have a prevailing visibility (without a specific direction). For example

3200 1200SW

Here's you example, but with the above visibility string, working correctly:

https://aeharding.github.io/metar-taf-parser/metar?input=CYVR+301300Z+09006KT+3200+1200SW+2000NE+FEW055+FEW120+M04%2FM06+A3049+RMK+SC1AC1+SC+TR+SLP327

It seems like it may be possible (?) to have more than one minimum visibility directions, but I'm not sure.

Do you have a specific example of a real METAR with a direction but without a prevailing visibility?

[drmrbrewer]

You may well be right, but it's frustratingly difficult to find a definitive resource.

This reference backs up your theory:

But this source only refers to "two groups" (not in addition to a prevailing group):

And then this source again suggests there is a prevailing visibility followed by a directional visibility:

On balance (and based on the "officialness" of the above sources) it does seem that you're correct that a directional visibility should follow a non-directional visibility.

Happy to close this if you are.

[aeharding]

Sounds good! Please let me know if you find anything weird like this in a real METAR and I will reopen this.