Floods can have a significant impact on human populations, affecting business, industry, and natural resources. This is especially true in the Susquehanna River Basin (SRB) watershed which contains approximately four million inhabitants within its confines. Warning times for floods are often too short and it can be difficult to predict exactly where and when a flood will occur. Therefore, it is important to improve flood forecasts in order to decrease the cost of damages and minimize loss of life. The goal of this project is to approach the issue of major flooding on a climatological level by assessing air mass frequencies to determine the relationship between any one air mass type and the timing of major flooding. Air masses are defined by the Spatial Synoptic Classification and frequencies during significant floods over the past 20 years will be calculated to compare to the long-term period of record frequencies. Flood periods are identified using flood stage, crest, and stream flow. A statistical significance analysis of the results will be performed using the computer programming language, IDL. Ultimately this information should improve the information used by meteorologists to forecast floods since there is high skill in predicting air masses. Preliminary results indicate moist air mass types are more frequent during significant flood events.