This paper investigates systematic tendencies and biases of NOGAPS central pressure forecasts for extratropical cyclones with central mean sea-level pressure not exceeding 1001 mb. Specifically, temporal and regional forecast biases are addressed for ocean and land lows, including deepening (pressure drop greater than -1 mb/12 hrs but less than -7.5 mb/12 hrs), rapidly deepening (pressure drop greater than -7.5 mb/12 hrs), and filling (pressure rise greater than 1 mb /12 hrs) systems. The regions of investigation include North America, Eurasia, the North Atlantic Ocean, North Pacific Ocean, and the Mediterranean Sea. The paper focuses on 48 to 96-hr forecast errors.
Results for September through May indicate NOGAPS is slow to deepen for deepening cyclones, with the tendency most apparent for rapidly deepening cyclones. This is especially evident at forecast times beyond 48 hrs. Conversely, NOGAPS is slow to fill for filling cyclones, with the exception of those in the North American region. Here, NOGAPS shows a slight tendency to over fill for filling cyclones. These tendencies are again most notable at forecast times beyond 48 hrs.