Originally Posted by HDQDD

Having worked in dispatch, I can shed some light on this. Most regionals don't bother to get their pilots Category III ILS certified. It's too expensive (used to be about $20K+ per pilot in early 2000s) and there's too much turnover to justify it with their thin margins. I'm also not sure if all regional airplanes have the equipment for it either. Almost all regional pilots are only Cat I certified (which is good enough 99% of the time). Cat I means they usually require at least 1800ft visibility and Vertical Vis of 200 feet to land* IIRC. It's (extremely) rare to not have at least these conditions. Probably less than one day every few years for 90+% airports. Cat III is auto-land, where little to no visibility (Cat IIIc) is required.

*When conditions are too bad to land, they are often too bad to takeoff as well. Here's why: In case of emergency, the pilots have to either A) be able to return to the field (which they wouldn't if conditions worse than those mentioned above) B) File with a TALT (Takeoff Alternate) which is essentially an airport nearby that they could land at in case of emergency. Problem with TALT's is that they're usually experiencing the same weather. When this happens, the flight cannot leave until either A or B is above minimums.

If this was the case, it's a weather delay. An avoidable one if money were no object, but peeps don't seem to like paying higher fares.