A little tip if you want your cards to be coloured like official ones: on VioletCLM's card generator, if a card has only one colour on its banner, put the type of it in the Primary box, then in the Secondary box put 'SAME'. With Log Cabin, you'll want to put Victory as the Primary, and Action/Event as Secondary.
Of all your cards here so far, the Avalanche set is my favourite. The interactions with all the cards and what they do are sound. How many Firn Villages are there though? And you might want to use the same wording as Fortress for it, 'when you trash this, put it into your hand', because if it's trashed by another player's Knight there could be some confusion over whose hand it goes to. Fortress's wording is safe here.
Edit after Asper's 'ninja': Lodge is a fine way to make a card use 2 Actions. I would suggest the bottom be worded "At the start of your Buy phase, for every unused Action you have, you may discard a Lodge from your Tavern mat." Then give it only +1 Action or make it a big terminal.
Snowy Owl is a simple and effective card, but with an extra Buy you can get 2 Lurkers for $4 anyway. Trash for benefit cards and games with no +Buys still like this of course.
Then writing this I realise Lurker shines in both these situations, so actually this a more elegant design again. Well done you.
Frigid Village is a strictly better Caravan, so that would push the cost to $5. Unless you add an on-gain effect to change this.
And reading your comments on it...are you designing this to be a set that plays by itself, or one to mix with other sets? Almost everyone on this forum will assume mixing with other sets, so that may affect the feedback you get.