Grouse are inherintly not overly bright creatures.
Rainy springs will come very close to wiping out the chicks because they don't have enough sense to take cover, except under the wings of the female, which will often lead to the demise of the female, if she isn't already under cover.
Adult grouse will seek cover from rain/cold and usually survive to produce another batch of eggs. If it's to cold, those eggs won't hatch.
Our area had a very wet/cold spring this year. Grouse populations are way down and I'm still seeing chicks that are only a few weeks old. Same goes for Quail.
The local Quail population that circulates through my yard was down to 5 birds, from a usual 75-100. Yesterday I counted over 40 birds, with at least 30+ chicks around two weeks old.
Hopefully the winter isn't to inclement and the survival rate is good.
Because of the cold/wet spring, many of the wild fruit shrubs and trees, such as huckleberries/choke cherries/saskatoon berries lost all their fruit. The wild animals and birds that depend on that fruit to put on weight to weather the cold are desperate for a replacement food and are resorting to thorn berries, which are mostly just hard seeds that don't digest.
just came back from a week long moose camp in the area, didnt see too many birds and what you say makes sense, plus a bunch of coyotes seem to be happy at home there, im thinking about cutting down their population a bit to give other animals better chance at surviving winter