Recent in situ measurements of water vapor, meteorological properties, and cloud particles provide evidence for large slushy ice particles at -40¿C in an intense tropical updraft. During a flight through Tropical Storm Chantal (20 Aug. 2001), the NASA DC-8 aircraft encountered strong convection, high humidities, high particle concentrations, and plugged probe inlets. This paper addresses the question of whether these observations can be explained with our current understanding of cloud microphysical processes. The microphysical evolution of particles in the updraft is simulated with a model to demonstrate that millimeter-sized slushy ice particles can exist at environmental temperatures below the ice homogeneous nucleation temperature. Supercooled liquid droplets are inferred to exist at higher temperatures in the updraft, below the DC-8 altitude.