Raynauds is IMHO a bit of a bogus catch-all. My guess is that Raynauds is mostly a stress induced Hypothalmic condition in most cases... I know that in my case, stress does bring on the temp drop...but of course whether it is mental stress or the stress of facing 50 below..the organism probably reacts in somewhat the same fashion.
Actually there is Raynaud's disease, which is an autoimmune disorder, and Raynaud's phenomena, which is the Raynaud's symptoms from a known cause such as hypothyroidism. Stress can increase epinephrine release, which causes a constriction of blood vessels. This can also bring on a feeling of being cold.