Issues in Mesoscale Verification: Implications of the Verification of High-Resolution MM5 Forecasts over the Pacific Northwest

Eric Grimit, Cliff Mass, Dave Ovens, and Mark Albright

Department of Atmospheric Sciences,

University of Washington

Seattle, Washington

cliff@atmos.washington.edu

During the past five years a real-time MM5 forecast system has been run twice a day at 36, 12, and 4 km grid spacing over the Pacific Northwest. These forecasts have been verified against a mesoscale observational database derived by collecting all available observations over the region. The verification approach has been based on interpolating model output to the observation location, in contrast to the grid box methods commonly used elsewhere.

This talk will provide a brief overview of the Northwest verification results and then turn to outstanding problems and issues regarding the verification of high-resolution model forecasts. It will be shown that although high-resolution simulations generally produce more realistic structures, timing and displacement errors in concert with traditional measures of forecast skill seriously penalize high-resolution forecasts. Furthermore, the effects of insufficient data density skew verification results to erroneously penalize high-resolution forecasts. If time permits, an idealized verification experiment will be presented as well as some suggestions for addressing the verification of high-resolution forecasts.

References:

Mass, C., D. Ovens, M. Albright, and K. Westrick, 2002: Does Increasing Horizontal Resolution Produce Better Forecasts?: The Results of Two Years of Real-Time Numerical Weather Prediction in the Pacific Northwest. Bull. Amer. Meteor. Soc., 83, 407-430.

Colle, B.A., C. F. Mass, and D. Ovens, 2001: Evaluation of the timing and strength of MM5 and Eta surface trough passages over the eastern Pacific. Weather and Forecasting, 16, 553-572

Colle, B. A., C. F. Mass, and K. J. Westrick, 2000: MM5 precipitation verification over the Pacific Northwest during the 1977-1999 cool seasons. Weather and Forecasting, 15, 730-744.

Colle, B. A. and C. F. Mass, 2000: The 5-9 February 1996 flooding event over the Pacific Northwest: sensitivity studies and evaluation of the MM5 precipitation forecasts. Mon. Wea. Rev., 128, 593-617.

Colle, B. A., K. J. Westrick, and C. F. Mass, 1999: Evaluation of MM5 and Eta-10 precipitation forecasts over the Pacific Northwest during the cool season . Weather and Forecasting, 14, 137-154.