On April 9, 1999, approximately 0930 central daylight time, a McDonnel Douglas DC9-32, N205ME, operated by Midwest Express Airlines, Inc. (MWEA), experienced a loss of elevator control while in cruise flight near Dubuque, Iowa. The 14 CFR Part 121 flight departed General Mitchell International Airport, Milwaukee, Wisconsin, at 0920, enroute to Eppley Airfield, Omaha, Nebraska. The flight crew piloted the aircraft using the elevator trim system until regaining elevator control after descent. The airplane landed at Eppley Airfield without further incident. There were no reported injuries to the 6 crew members or to the 85 passengers. The pilot stated that the aircraft departed General Mitchell International Airport in "moderate wind driven rain." The pilot said that when the aircraft was leveled off, after climb, the elevator control "...was found to be frozen and would not move." The pilot further stated that when a descent was made to "warmer air", the "... elevator thawed out..." and normal control was regained. A weather report for General Mitchell International Airport, MKE, at 0856, showed a temperature of 39 degrees Fahrenheit, rain, mist, and winds from 030 degrees magnetic at 20 knots gusting to 28 knots. An inspection of the aircraft after the incident failed to reveal any anomalies with respect or the aircraft or aircraft systems. On two other occasions, MWEA DC9 aircraft experienced elevator control difficulties. On these occurrences, the aircraft departed in rain with temperatures of 46 degrees Fahrenheit and 39 degrees Fahrenheit respectively. On one of the occurrences, MWEA maintenance personnel found ice accretions in the elevator control bay of the vertical stabilizer (Reference: CHI99IA115).