Mine has done this as well, quite a bit here lately. We're getting ready for a big snow storm tomorrow, Southern Colorado, and it was really showing bizzare values for the last three days, up until the storm was about 24-36 hours away. It's been much more stable today, but I do occasionally catch a glimpse of it throwing out some goofy numbers. lol
Plus, it's not just my station doing it. The surrounding stations 10 day forecast will also show weird readings when it happens.