I do not understand this thread. Like the poster above me, I just wear a thin merino layer if it is cold and raining. A jacket may make it easier for the first 5 minutes, but it quickly ruins your run by getting wet and making you sweat like you're wearing a sauna suit.
If it is over 32, you'll warm up after 5 minutes.
A good read from Duke alum Andrew Skurka (who is also an outdoor gear expert):
Why waterproof-breathable fabrics fail
In my experience, waterproof-breathable fabrics are neither waterproof nor breathable, especially during extended use and/or if the garment is not brand new. While there are measurable performance differences between the degrees of water-resistance and breathability of different fabrics, the ultimate outcome is the same: I will get wet from the outside, the inside, or both. It’s really just a question of timing and method.
Outside: The Achilles heel of WP/B fabrics is the durable water repellent (DWR) treatment applied to the face fabric. This long-chain (C8) fluorocarbon-based treatment easily degrades due to abrasion and contaminants (e.g. dirt, body oils, sunscreen), which causes the face fabric to become saturated with moisture. Since it is more humid outside the jacket than inside it, moisture is “pulled” through the jacket by the drier air inside. With new restrictions C8 soon taking effect, the lackluster performance of DWR will decline further.
The DWR finish can be restored with wash-in and spray-on treatments like Nikwax TX Direct Wash In. They definitely help, but I have found that the DWR is never as-good-as-new again. And without a functional DWR, wet-out is inevitable.
Inside: Technically, waterproof/breathable fabrics are breathable — i.e. moisture can transmit through the fabric, via solid state diffusion or direct venting. But so too is a jacket made of trash bag material with a few pinholes in it. Regardless of marketing claims to the contrary, the breathability of WP/B fabrics is utterly inadequate relative to a normal rate of perspiration when hiking, especially in warm and/or humid conditions. So even if you managed to stay dry on the outside while wearing WP/B clothing (like if it’s a sunny day) you will get wet from the inside due to trapped perspiration.