A two-dimensional, steady state boundary layer model is used to investigate the formation of cloud plumes over open Arctic leads. Satellite observations from the period of an intense storm in the Beaufort Sea during April 1992 are used to document lead plume formation <Fett et al., 1997>. These observations show a marked variability of open leads with and without cloud plumes dependent on synoptic weather conditions. Model simulations are conducted (using soundings before and after the storm's passage) which show extensive plumes forming in the postfrontal environment but not in the prefrontal atmosphere. To better isolate important factors contributing to plume development and plume dynamics, a large set of idealized model experiments is performed. This matrix of model simulations permits exploration of the parameter space of plume formation. The model is found capable of forecasting the onset of steam fog over a lead in a manner which agrees with empirical relationships. Such steam fog, however, dissipates quickly upon advecting over the surrounding ice and does not therefore appear generally responsible for extensive plumes observed to emanate from leads. Instead, extended cloud plumes form at the top of the convective thermal internal boundary layer (TIBL) that develops over a lead. These elevated plumes are quite sensitive to the relative humidity of the environmental air. Unlike steam fog, the elevated plumes also are found to be sensitive to the lapse rate of the environmental air. Changes in wind speed have little impact on the integrated heat and moisture amounts transferred to the atmosphere from a lead (provided advection balances flux divergence) but do impact the cloud plumes by altering shear-driven entrainment. For wide leads, indications are that lead refreezing must be in an advanced stage before having a major impact on the plume formation process. Additionally, we investigate the conditions under which a cloud plume that is detached from its parent lead may form downwind of a lead. Often, the plumes are predominantly water clouds near the lead, with the ice crystal fraction increasing as the plume cools downstream. A simple formula for estimating plume penetration depth is found to agree reasonably well with the model simulations for 1 km wide leads but deviates considerably for wider leads.¿ 1997 American Geophysical Union