The lightest jackets are under 4 ounces. Just remember the lighest stuff usually rips in a crash. The 8oz jackets are a little tougher. Also get a cycling vest with mesh back, you'll use them layered together and make adjusting to the weather and your effort level easy.
.....wanna be able to pack a lwater resistant, wind resistant light jacket.....sorta a just in case jacket.....some great suggestions.....any more out there.....anything from Endura, Pearl Izumi, Gore ect...that you have experience with and can recommend....thanks...Ride On!
There are two paths you can go by but in the long run........
North Face VERTO is an excellent “just in case” summertime downpour jacket, put it in your bag(or jersey pocket) and forget about it, packs down so fricken small and weighs nothing! The hood is a bit tight over helmet, but it’s thin so under works, also the sleeves have a lot of material that flap around in wind. This is not really my go to jacket on wet rainy day rides for long periods of time, for me it’s a “emergency” jacket for rain showers or higher elevation chill. The North Face® Summit Series Verto Jacket - YouTube
Been there, done that... don't remember it. Tallboy LTc & Bronson