Oh, from Ian Corless' review of a Salomon hybrid rain jacket:
(http://iancorless.org/2015/02/15/salomon-s-lab-hybrid-jacket-m-and-hybrid-pants-m-review/)
"So, should bad weather come in and lets say a worse case scenario of torrential rain, snow, blizzards and zero temperatures I personally don’t feel that the HYBRID would provide me (or maybe similar runners) with enough protection. This is not questioning its waterproofing, the jacket is waterproof BUT only in key places.
So you see the dilemma. If you are moving quick and retaining core temperature, the HYBRID Jacket M will be ideal allowing adequate protection in a lightweight, breathable and seriously functional product. But if your pace drops, you have extended walking and your core temperature starts to drop, this jacket may well not be the best for you… something a little heavier, a little more robust and 100% waterproof may well be the better product."
(if you don't know Ian Corless, check out his podcasts, loads of good interviews with mountain running athletes).