Rudland rigg will be good in this weather. Have you a gps device. I got a good route from this website.
http://www.mtb-routes.co.uk/northyorkmoors/default.aspx
Done the Farndale one and the Nawton loop one. This one may be a bit claggy though.
Edit. Just remembered that the start of the Nawton route was really muddy when we did it in late spring. Really warm day, but after some rain. Think there is a diversion you can take though. Brill ride though. Well worth having a crack at.