Hi. At this time of year I would definitely wear a waterproof jacket. There's loads on the market now but I always found a waxed jacket the best in the rain. Choose a jacket with vents and a long enough flap at the back to go over the cantle of the saddle-so your bum doesn't get wet! I find a two way zip is a must too. And a secure pocket to keep your gloves in. Waxed jackets can be quite heavy tho for when the weather is changeable. Lighter, waterproof jackets are available with the same features.