Title: The predictability of North American land-falling cyclones

Authors: Brian Ancell (Texas Tech University)
Lynn McMurdie (University of Washington)
Rolf Langland (Naval Research Laboratory)

Abstract: Land-falling North Pacific storms often impact the west coast of North America with strong winds, heavy precipitation and large mountain snowfall. These storms are frequently poorly predicted by operational models despite continued improvements in model resolution, model physics and data assimilation. Previous studies have shown that short-term (24-72hr) forecast errors of sea level pressure along the U.S. west coast are statistically related to large-scale upper-level flow regime. We expand on this prior work by using other methods to define predictability and relating this predictability to the specific characteristics of the cyclones themselves. Specifically, we examine 12- to 48-hr forecasts of land-falling North American west coast cyclones over 2 winter seasons. The tools used to assess predictability of the cyclones are 1) ensemble sensitivity produced from a WRF-model ensemble Kalman filter (EnKF), 2) adjoint sensitivity produced with an MM5 adjoint model, and 3) spread growth in the cyclone sea-level pressure field within the same WRF-model EnKF. We use these tools to further distinguish why certain cyclones may exhibit poor predictability, and whether large intrinsic potential for error growth or slower-growing, larger errors present at initialization are more important. Results over the 2-year period are shown, and plans to extend this work beyond this initial examination are discussed. The goal of this project is to determine some of the factors that contribute to predictability of a variety of weather regimes on multiple scales. Determining these relationships could be very important to address the modeling/data assimilation configuration during specific weather regimes associated with poor prediction of cyclones.

GMAO Head: Michele Rienecker Global Modeling and Assimilation Office NASA Goddard Space Flight Center

Curator: Nikki Privé Last Updated: March 1 2011