Icing - yes they would have been in icing conditions. The engine anti ice would have been on as a matter of course, in cloud with OAT below +10.
Airframe icing is really not an issue with the 73NG, at least not in those sort of conditions.
Windshear (since it has been mentioned) - to cause such an accident would have had to have been pretty dramatic. Unlikely if not impossible in prevailing conditions.