Due to the very low density of meteorological observations in the Arctic, the design of optimal research aircraft flight trajectories during FIRE-III was particularly difficult. To provide a real-time guidance for the Canadian Convair research aircraft (based in Inuvik N.W.T.) missions, an experimental mesoscale forecast system was run daily during the Canadian phase of the experiment (April 6 – May 1st 1998). A nested version (35 km and 10 km) of the Canadian MC2 model was run each day to produce specialized forecasts of various meteorological parameters with an emphasis on the mesoscale cloud structure and boundary layer fluxes. The clouds were forecast with the mixed-phase cloud scheme developed by Tremblay et al. (Tellus, 48A, 483-500). This scheme considers the total water content (TWC) as a basic prognostic variable. The TWC is diagnostically partioned into solid and liquid phases at subfreezing temperatures and encompasses the continuum of all solid and liquid phase particles that constitute the mass of condensate in the atmosphere.
Modeled and observed Arctic clouds for this period were mostly composed of ice crystals. Their water content was low. The supercooled liquid water was observed and modeled on few occasions and it was generally confined to localized regions near the surface. Multiple cloud layers was a common property of the cloud field and temperature inversions were frequent. The structure and microphysics of low-level Arctic stratus will be compared with available data, especially in situ aircraft observations.