1. An Investigation of Cool Season Extratropical Cyclone Forecast Errors Within Operational Models Brian A. Colle 1 and Michael Charles 1,2 1 School of Marine and Atmospheric Sciences Stony Brook University – SUNY 2 National Centers for Environmental Prediction

2. Motivation Complete a long-term (5-year) cyclone verification of the operational NCEP GFS and NAM models (several years since the last objective evaluation). What synoptic flow patterns are associated with particular cyclone errors in operational models? What is the impact of using the NCEP Short- Range Ensemble Forecast (SREF) system for cyclone prediction?

3. Automated Cyclone Verification using NCEP Tracking algorithm (Marchok 2002) fcst - 960 mb obs - 955 mb fcst - 982 mb obs - 982 mb fcst - 982 mb obs - 984 mb http://www.emc.ncep.noaa.gov/gmb/tpm/emchurr/tcgen/

4. Data Cyclone Events (Oct-Mar 2002-2007) - GFS (0-120 hr every 6 h) at 80 km grid spacing - Eta/NAM (0-60 h every 6-h) at 40-80 km grid spacing - Same cyclones and times were used to compare models. Interpolate to common 80-km grid SREF (Oct-Mar 2004-2007) - 15 members (5 Eta-KF, 5 Eta-BM, 5 RSM) - ~40 km grid spacing (212 grid) - Available at 09 & 21 UTC ( 63 h forecast) - Included 6 SREF WRF members for 2006-2007

5. NAM-GFS analysis cyclone central pressures for 2002- 2007 cool seasons Central and Eastern N Amer Western N Amer Pacific W. Atlantic Central and Eastern N Amer Western N Amer Pacific Mean Analysis SLP Error as compared to surface observations for cyclones within 500 km of station Mean Abs Error Mean Error

6. Cyclone Central Pressure Mean Absolute Errors in mb (18-36 h ) GFS NAM

7. Cyclone SLP Abs Error versus Fhour By Region NAMGFS E. Pacific Cent N.A. W. Atlantic W. N.A. CP 1 2 3 4 5 6 CA

8. Cyclone Central Pressure Mean Error in mb (48-60 hrs) GFS NAM

9. Western Atlantic Cyclone Position Errors (42-60 h) NAM GFS All Cyclones Deep (1.5 stnd dev) Cyclones

10. GFS SLP MAE 12 UTC versus 18 UTC Runs GFS cyclone displacement error (km) for 12 UTC versus 18 UTC Runs E. Pacific W. Atlantic Cent N.A. 18 UTC 12 UTC 2002-2006 GFS Atlantic hurricane track error X X X X X X X X 1995-1998 GFS Atlantic hurricane track error * * GFS extra-tropical 1989-90 (Mullen and Smith 1993)

11. Cyclone SLP Abs Error in mb (48 h) NAM GFS E. Pacific E. US. and W Atl Central U.S.

12. Cyclone Displacement Error in km (48-h) NAM GFS E. Pacific W. Atlantic

13. GFS Median Range Mean Absolute SLP Error (970 mb) (990 mb) (992 mb) (975 mb) (973 mb) ALL CYCLONES DEEP CYCLONES (> 1.5 stnd dev) E. Pacific W. Atlantic E. N.A. Cent N.A. W. N.A. E. Pacific W. Atlantic E. N.A. W. N.A. Cent N.A.

14. GFS Median Range Mean SLP Error (Deep storms) ( 970 mb) (990 mb) (992 mb) (975 mb) (973 mb) E. Pacific W. Atlantic E. N.A. W. N.A. Cent N.A.

15. 96-h GFS forecast (12z 16 Jan 2004)

16. Hour 72 Hour 30 Hour 96 Random Error DaysLarge Error E. Pac (>1.5 std dev)

17. GFS Large Error Cyclone Events for 48-h (Regions 5,6) GFS negative SLP error (1.5 std dev > mean error, or < -5.1 mb) GFS positive SLP error (1.5 std dev > mean error, or > 4.5 mb) Model pressure tendency error (mb/6h)

18. SREF and GFS/NAM Displacement Error (W. Atlantic) SREF and GFS/NAM Central Pressures Mean Absolute Error (W. Atl) GFS SREF NAM GFS SREF NAM

19. 51-h SREF (valid 2006011500) X X X EKF EBM RSM NAM GFS OBS -10 to 0 mb 0 to 10 mb 10 to 20 mb

20. Rank Histogram of cyclone central pressure and best member likelihood percentage (W. Atlantic) RSM Eta-KFEta-BM Hours 33-45

21. Conclusions GFS analysis for cyclones is significantly better than the NAM or NARR, especially over the oceanic regions. The NAM and NARR cyclones are too weak on average. GFS cyclone forecasts have more skill than the NAM in all regions. NAM cyclones are too weak over the E. Pacific on average. By hour 84, W. Atlantic errors become comparable to the E. Pacific and the errors become greater than E. Pacific for deeper cyclones. The 09/21z SREF has larger cyclone MAEs than the deterministic GFS and slightly less than NAM. The SREF pressures tends to be overdispersed in many locations. Some model cyclone biases for the eastern U.S. may favor specific storm tracks. Large cyclone errors over the E. Pacific can impact the western Atlantic 2-3 days later.

22. EXTRA SLIDES

23. Cyclone Identification (NCEP Approach) SLP field from grib file Locate grid point with lowest SLP Try to find 2mb closed isobar Mask out cyclone and repeat 2 1 3 4 Same used at NCEP - http://www.emc.ncep.noaa.gov/gmb/tpm/emchurr/tcgen/http://www.emc.ncep.noaa.gov/gmb/tpm/emchurr/tcgen/

24. Cool Season Cyclone Numbers per 2.5 o grid