Lightweight packable roadie waterproof

+1 for montane. You’d
+1 for montane. You’d probably want to couple it with a ls jersey or arm warmes though, as they stop the sweat sticking it to you.

I have one of these. Packs
I have one of these. Packs down small enough to fit into a jersey pocket, and Warterproof enough for some pretty bad weather. The fit isn’t baggy but its not skintight.

http://www.wiggle.co.uk/altura-pocket-rocket-waterproof-cycling-jacket/

I’m a big fan of the Montane
I’m a big fan of the Montane Featherlite Velo. I’ve had mine for 3 years and it’s been so good. Packs really small into a pocket, comfortable fit and doesn’t cost a great deal.

I’d definitely buy another if this one were to somehow fail.

both the Castelli and Mavic
both the Castelli and Mavic jackets are similarly ‘racer’ cut to the Gore, although not quite as extreme, designed to be snug and not flappy in the wind which you might find tricky fitting over winter gear, not tried the Altura but as a brand they tend to be more generously cut

have a look at Montane, they do a good range of lightweight pocketable wind/waterproofs that will fit over lots of clothes

the cut on some Gore jackets
the cut on some Gore jackets can be very ‘racer’ tight so if you’re carrying a few extra pounds or even too much stuff in your rear pockets they can be tricky to zip-up

that jacket’s really more water-resistant than waterproof and designed more of a breathable windproof, although it will keep drizzle off for a couple of hours, and it does pack down small and light