The WRF-based incremental analysis updates and its implementation in an hourly cycling data assimilation system

With the application of IAU, the analysis increment is smoothly introduced into the model integration over a time window centered at the analysis time.

As in digital filter initialization (DFI), the IAU scheme is able to limit large shocks in the early part of a model forecast. Compared to DFI, IAU does better in hydrometeor spinup and produces more continuous precipitation forecasts from cycle to cycle. The run with IAU is shown to improve the precipitation forecast skills (101% for CSI scores) compared to the regular cycling forecasts without IAU.