1. A Comparison of In-Situ Data with Meso-Scale Forecasts
Keith Williams
20 SEP 01

2. Objective: To determine the skill of meso-scale models in
forecasting strong low level inversions and associated increased
Wind speeds.
Background: On leg two of the OC 3570 cruise, surface winds
in excess of 30kts were observed while rawinsonde data showed a sharp inversion at ~500m (~950mb) and rapid decrease in wind speed with height.
Comparison: MM5 Analyses and 36, 24 & 12 hour forecasts were compared with 4 sondes that were launched closest to synoptic hours. MM5 fields of interest were MSLP, 980mb, 840mb, Skew-T, and vertical cross sections.

3. LEGEND
Each slide is for one valid time.
Forecasts from previous model runs are shown with each valid time.
Example: “06/00z 36hr fcst” is the 36 hour forecast from the 04/12z model run and is for the valid time 06/00z.

4. Balloons of Interest #6 07/21Z #7 08/00Z #5 07/17Z #4 07/01Z #3 06/20Z

5. 06/00z 36hr fcst
06/00z 24hr fcst
06/00z 840mb
06/00z 12h fcst
06/00z anal

6. 06/00z 36hr fcst
06/00z 24hr fcst
06/00z 980mb
06/00z 12hr fcst
06/00z anal

7. 06/00z 24hr fcst
06/00z 36hr fcst
06/00z MSLP
06/00z 12hr fcst
06/00z anal

8. 06/00 36hr fcst
06/00 24hr fcst
Balloon 1
06/01z
06/00 12hr fcst
06/00 anal

9. Balloon 1

11. 06/12z 36hr fcst
06/12z 24hr fcst
06/12z 840mb
06/12z 12hr fcst
06/12z anal

12. 06/12z 36hr fcst
06/12z 24hr fcst
06/12z 980mb
06/12z 12hr fcst
06/12z anal

13. 06/12z 24hr fcst
06/12z 36hr fcst
06/12z MSLP
06/12z 12hr fcst
06/12z anal

14. 06/12 36hr fcst
06/12 24hr fcst
Balloon 2
06/13z
06/12 12hr fcst
06/12 anal

15. Balloon 2

16. Balloon 3

18. 07/00z 36hr fcst
07/00z 24hr fcst
07/00z 840mb
07/00z 12hr fcst
07/00z anal

19. 07/00z 36hr fcst
07/00z 24hr fcst
07/00z 980mb
07/00z 12hr fcst
07/00z anal

20. 07/00 36hr fcst
07/00 24hr fcst
Balloon 4
07/01z
07/00 12hr fcst
07/00 anal

21. 07/00z 36hr fcst
07/00z 24hr fcst
07/00z MSLP
07/00z 12hr fcst
07/00z anal

22. Balloon 4

23. V2 V1
#4 07/01Z V3

24. 07/00 36hr fcst
07/00 24hr fcst
Vertical 3
07/00z
07/00 12hr fcst
07/00 anal

26. 07/12z 36hr fcst
07/12z 24hr fcst
07/12z 840mb
07/12z 12hr fcst
07/12z anal
NOT AVAILABLE

27. 07/12z 36hr fcst
07/12z 24hr fcst
07/12z 980mb
07/12z 12hr fcst
07/12z anal
NOT AVAILABLE

28. 07/12z 36hr fcst
07/12z 24hr fcst
07/12z MSLP
07/12z 12hr fcst
07/12z anal
NOT AVAILABLE

30. 08/00z 840mb
08/00z 36hr fcst
08/00z 24hr fcst

31. 08/00z 980mb
08/00z 36hr fcst
08/00z 24hr fcst

32. 08/00z MSLP
08/00z 36hr fcst
08/00z 24hr fcst

33. Balloon 7
08/00z
08/00 36hr fcst
08/00 24hr fcst

34. Balloon 7

36. Conclusions:
MM5 was able to identify the low level inversion.
The model correctly forecast the wind direction with height.
Although increases in winds were forecast, the model was off by as much as 10kts at times.
Vertical cross-sections are easier to interpret than vertical soundings.
The excellent performance of this mesoscale model should not replace the value added by the forecaster. Specifically, the under-forecast of the model with respect to surface wind speeds could be compensated for by a forecaster.