ETA and GFS Validation (Southeastern Mexico)

1. ETA and GFS Validation(Southeastern Mexico) John M. Dickens RSIS/CPC

2. Outline • Models • Data • Methods • Results • Conclusions

3. Purpose • To determine whether it is appropriate to replace the 20 km ETA model with the 50 km GFS model for forecasting precipitation amounts in Central America and the Caribbean.

4. Models • ETA 20 • 20 km • CPC Domain • GFS 50 • Global • 50 km Show model domain

5. Data • Central America GTS Stations (75): The data from these stations are quality controlled downstairs and in the CPC, making them more reliable than their NOAA/USGS counterparts. Due to the sparse data these stations will not be used. • NOAA/USGS Stations (101): These stations were set up as part of the Hurricane Mitch Program. No money was set aside for maintenance of these stations so their reliability is in question. Also, the exact units of the measurements have never been determined. Therefore, these stations will not be used. • Mexico Co-Op Stations (~500 out of 1000): The Mexico stations will be used because they are fairly dense in the southern half of the country and therefore will be a decent representation of the Central American region.

6. Data • Only used stations reporting precipitation amounts greater than zero • Time period: May 1 to August 31, 2004

7. Data • The forecasts represent the precipitation for the past 6 hours. • F06 represents rainfall from F00 to F06 • F12 represents rainfall from F06 to F12 • ……. August 1 Forecast August 1 Mexico Data: The Mexico data runs from 12Z to 12Z. August 2 Forecast August 2 Mexico Data: The Mexico data runs from 12Z to 12Z. August 3 Forecast * For the August 1st forecasts of 24 hrs and 48 hrs the Mexico data for August 1st and 2nd are required.

8. Methods • Match Co-op stations to model grid points in a point-to-grid comparison = model grid points = Co-op stations

9. Methods • Regular • 24 hr / 48 hr forecasts • No Coast • 24 hr / 48 hr forecasts • No Mountains • 24 hr / 48 hr forecasts

10. Data Points

11. Methods • Regular vs No Coast vs No Mountains • 24 hr and 48 forecasts • 24 hr vs 48 hr forecasts • ETA and GFS • Overall

12. 24 hr Mean Difference

13. 24 hr Standard Deviationof the Mean Difference

14. 48 hr Mean Difference

15. 48 hr Standard Deviation of the Mean Difference

16. Categorical Summary

17. 24 hr vs 48 hr Forecasts 24 hr ETA 48 hr ETA 24 hr GFS48 hr GFS

18. Conclusions • Mean differences increase with increasingly large events • Standard deviations of mean difference increase with increasingly large events

19. Conclusions • Regular • Overall GFS smaller mean difference • Overall ETA smaller standard deviation of the mean difference • No Coast • Overall GFS smaller mean difference • Overall ETA smaller standard deviation of mean difference • No Mountains • Overall ETA smaller mean difference • Overall ETA and GFS have identical standard deviations of mean difference

20. Conclusions • ETA 48 hr forecasts more accurate than the ETA 24 hr forecasts • Known initialization problems….additional 24 hrs for spinup • ETA forecasts precipitation in the region better than the GFS • Mean differences: both < ±6 mm • Standard Deviations: both > 15 mm, ETA ~ 5 mm lower • Correlations: ETA .25-.30, GFS near zero

21. Thank You