Pins & Needles in Forearms

Now that our long runs are getting longer, I'm starting to feel a sensation in my forearms again that I've felt during past training cycles. It feels almost like pins and needles shoot up my forearms, and happens later on in a long run when I go to check my watch or shake out my arms. I tried to do some googling, but can't figure out if it's an electrolyte thing, another nutrient/hydration thing, or something else. Curious if anyone else has experienced this or if there's something I should be doing to prevent it!