Office note (National Centers for Environmental Prediction (U.S.)) ; 337

National Weather Service (NWS)

Forecasts with the Nested Grid Model were made in which the interval between calculation of (vertical mixing plus precipitation) were varied from 1.25 minutes to 60 minutes on grid C. As the interval is lengthened, the convective precipitation in a fixed time (e.g. 12 hours) increases, but the grid-scale precipitation decreases more, resulting in a decrease of precipitation. Small decreases in cyclogenesis are noted when the interval is long. These effects are not present when only the vertical mixing interval is lengthened. Thought could be given to reducing this effect on precipitation by adding an anticipatory estimated effect every dynamical time step.