This paper presents three-dimensional prognostic O<sub>3</sub> simulations with parameterized gas-phase photochemistry from the new NOGAPS-ALPHA middle atmosphere forecast model. We compare 5-day NOGAPS-ALPHA hindcasts of stratospheric O<sub>3</sub> with satellite and DC-8 aircraft measurements for two cases during the SOLVE II campaign: (1) the cold, isolated vortex during 11-16 January 2003; and (2) the rapidly developing stratospheric warming of 17-22 January 2003. In the first case we test three different photochemistry parameterizations. NOGAPS-ALPHA O<sub>3</sub> simulations using the NRL-CHEM2D parameterization give the best agreement with SAGE III and POAM III profile measurements. 5-day NOGAPS-ALPHA hindcasts of polar O<sub>3</sub> initialized with the NASA GEOS4 analyses produce better agreement with observations than do the operational ECMWF O<sub>3</sub> forecasts of case 1. For case 2, both NOGAPS-ALPHA and ECMWF 114-h forecasts of the split vortex structure in lower stratospheric O<sub>3</sub> on 21 January 2003 show comparable skill. Updated ECMWF O<sub>3</sub> forecasts of this event at hour 42 display marked improvement from the 114-h forecast; corresponding updated 42-hour NOGAPS-ALPHA prognostic O<sub>3</sub> fields initialized with the GEOS4 analyses do not improve significantly. When NOGAPS-ALPHA prognostic O<sub>3</sub> is initialized with the higher resolution ECMWF O<sub>3</sub> analyses, the NOGAPS-ALPHA 42-hour lower stratospheric O<sub>3</sub> fields closely match the operational 42-hour ECMWF O<sub>3</sub> forecast of the 21 January event. We find that stratospheric O<sub>3</sub> forecasts at high latitudes in winter can depend on both model initial conditions and the treatment of photochemistry over periods of 1-5 days. Overall, these results show that the new O<sub>3</sub> initialization, photochemistry parameterization, and spectral transport in the NOGAPS-ALPHA NWP model can provide reliable short-range stratospheric O<sub>3</sub> forecasts during Arctic winter.