Understanding Alpine Ice Ratings

I've been looking into alpine climbing recently and I've been a bit confused by the alpine ice ratings (AI#) on many of sierra objectives, for example the North Couloir of North Peak. mountainproject.com/v/north…

My question comes down to what grade would generally necessitate full belayed technical ice climbing and in which conditions? For example for the North Couloir I see pictures online of people pitching it out, but it seems to be in late season blue ice conditions? Would neve conditions generally mean this isn't necessary? Do people often use pickets, etc. in neve conditions on these sorts of climbs when it would be icescrews in blue ice conditions?

To make things more confusing, some sources say that alpine ice is generally easier than the equivalent waterfall ice ( alpinist.com/p/online/grades ), but intuitively it should be very season dependent.

Thanks for your help,
Ben

I think you answered your own question. Alpine ice and other winter routes can range from a nice hike, to a technical ice pitch, to unprotected mixed climbing to bowling alley depending on conditions. If you have the requisite mountain experience, you will get there with a general idea of what to expect, and then figure out what you need to do (i.e. pitch it out, stomp joyously up slope, retreat, etc) depending on what you find.

As for some of your more detailed questions, pickets are usually only useful to the extent there is decent snow to sink them in. In those conditions, you are usually using a picket as an anchor and running it out anchor to anchor. Then you can get thin ice where its good and easy to climb, but wont take good screws. Ice conditions good enough you may get some screws, but typically want to belay off rock gear on the sides of the couloirs if you can find good gear (its generally more protected than being exposed to rock/ice fall in the couloir). At the end of the day, on less technical alpine routes speed is safety and the climbing isn't so hard that placing a lot of gear is going to happen. The mixed alpine rack is some small and medium camps supplemented with some nuts and tricams. Maybe a pin or two and two or three screws. Modify from there depending on what conditions you expect to find.