On a recent trip, I tried to go pretty light and struggled with whether or not to bring hard shell tops and bottoms. I have a Patagonia Rain Shadow jacket and some full zip North Face pants (total weight about 1.5 lbs). It was two-day trip and the forecast called for good weather, no wind, not too cold, and no snowcover anywhere on the route (Southern Sierra). As always, the hard shells stayed in the pack from car to tent to summit and back. I knew they would, but I just couldn't bring myself to leave them behind.
I'm curious how others make this decision. For a weekend trip*, do you pack your hard shells only when the forecast calls for foul weather? Do you always bring them just in-case? Do you only bring the jacket and leave the pants behind?
*For an extended trip the decision seems pretty obvious to bring them, and for a day trip the forecast should suffice.
I always bring a hard shell jacket since I climb in the notoriously fickle weather of the PNW. It weighs only 10.3 oz so why not. It is useful against high winds even if it doesn't rain or snow. I never bring hard shell pants while climbing in the lower 48 year round. I do wear hard shell pants in Alaska though.
Since my climbing is in the Sierra and typically only a couple of days I usually carry my Precip shell jacket. It is lightweight and I incorporate it into my layering system so I am not carrying unnecessary items and have a little extra protection against the elements. I only bring my pants if I am going to be out for an extended period where the forecast could change, or if they likelihood of wet weather is increased to the point I might need them. Again, I attempt to coordinate them into my overall clothing system if at all possible (ie warm days with cool nights, I don't bring pants for camp in the evening and instead use my hard shells if it is cool).
Always. These are some of the lightest, most packable gear I own, so why not? Even on cloudless summer days they come in handy in windy conditions above treeline, and they make a good extra layer for cold mornings in camp. Again, lighter and more compact than a warmth-equivalent fleece for either purpose.