Johnston Fire Department was alerted of a mutual aid rural fire assignment to Grimes. E3930, Tender 3950 were requested on the first alarm and were enroute in minutes, before units arrived on scene C3700 per dispatch information quickly struck a 2nd alarm and tanker task force. RE3970 enroute on the second alarm. Weather conditions made travel conditions trecherous. Initial arrival report of E3730 described heavy fire and smoke showing from garage area. Rapidly deteriorating weather conditions made operations painstakingly difficult. Two drafting operations were set up. Tankers from Grimes, Johnston, Waukee, Granger, Dallas Center, Polk City, and Saylor responded. Urbandale R418 responded as RIT.