Ensemble simulations of arctic circulation can develop multiple dynamical regimes. We use ensemble simulations of June -- December 2007 by the WRF-ARW model to examine regime development, and to understand the differences in the atmospheric circulation caused by changes in sea ice and how it is represented. Multiple regimes are common in our ensemble simulations, although there are differences through the period. There is a slight tendency for two or three regimes to be preferred more in June-July-August than October-November-December. September has the fewest multiple-regime periods. September is also the month of sea-ice minimum, suggesting that open ocean may inhibit the occurrence of multiple regimes in ensemble simulations compared to periods when substantial sea ice is present. Differences in sea-ice treatment have little influence on model results. The regime behavior occurring here suggests that as future summer ice cover wanes in the Arctic, the predictability of the atmosphere may increase.