Just to follow up here, PWS ELMERWDX1 seems to only be on from ~7am ~5pm. Maybe it's hooked up to solar power? Seems to correspond to those times. I see there's another PWS that is only just a bit further away - maybe we'll be able to select the one we'd like to use in a future update.
In either case, I really like the idea of being with an "official" one that's at an airport - I know it's maintained and calibrated.