1. A Sensitivity Study on the NOAA/GLERL Wind Wave Model used in the Graphical Forecast Editor David Zaff (NWS) and Keith Jaszka (summer student) NOAA/National Weather Service Buffalo, NY Oct 08, 2008

2. Goal Learn a bit about the NOAA/GLERL Wind Wave Model Fun Fact: The Great Salt Lake is the largest producer of brine shrimp in the world.

3. Main variables Only 3 variables are needed for the GLERL Wind Wave Model: –Air Temperature –Wind Speed –Lake Temperature

4. Unstable or Stable Marine Boundary Layer Cold lake, warm air –Inversion –Small waves Warm lake, cold Air –Unstable –Friction –Big waves Climate/Temperature for Lake Erie

5. Assumptions Test for Lake Ontario Set lake to 0 C for entire study and varied: –the air temperature –The wind speed. Constant wind at 240 degrees –(typical direction) Ran model until wave heights reached equilibrium state No ice.

6. 400 Simulations later… Results strongly support rule of thumb: –Winds>18 kts (9.5 m/s) produce: waves in excess of 4 ft (1.2 m) –Regardless of air/lake temperature difference SMALL CRAFT ADVISORY (18-33 kts and/or waves > 4 ft (3-5 ft)

7. Lets see some data…

8. Small Craft Advisory (>= 4 ft/(1.2m) (Warm Lake and Cold Airmass) Wind speed (0-10 kts) (Cold Lake and Warm Airmass)

9. (Warm Lake and Cold Airmass) (Cold Lake and Warm Airmass) Wind speed (0-15 kts) Small Craft Advisory (>= 4 ft/1.2m)

10. (Warm Lake and Cold Airmass) (Cold Lake and Warm Airmass) Wind speed (0-40 kts) Small Craft Advisory (>= 4 ft/1.2m)

11. (Warm Lake and Cold Airmass) (Cold Lake and Warm Airmass) Wind speed (10-20 kts) Small Craft Advisory (>= 4 ft/1.2m) 1.Focus in on area that straddles the SMALL CRAFT ADVISORY 10-20 kts. 1.If you forecast 10-20 kts – should you issue a SCA? 2.Stable airmass – you’re OK 3.Marginally stable or unstable airmass? Don’t know

12. Wind speed (10-20 kts) (Warm Lake and Cold Airmass) (Cold Lake and Warm Airmass) Small Craft Advisory (>= 4 ft/1.2m) THE FORECAST….SOUTHWEST WINDS 10 TO 20 KNOTS Worse case scenario: 10kt winds  2.2 ft 20kt winds  6.5 ft

13. Case Study #1 August 16, 2008 Upper level low passing by to east –Lake temp: 73F/23C –Forecast High: 75F/24C (after a morning low of 56F/13C) UNSTABLE in the Marine Boundary Layer 500mb Height 500mb Height Anomaly

14. Case Study #1 August 16, 2008 The nearshore forecast (off lake Erie):.TODAY...NORTHWEST WINDS 10 KNOTS OR LESS BECOMING SOUTHWEST AND INCREASING TO 10 TO 20 KNOTS. PARTLY SUNNY WITH AN ISOLATED SHOWER OR THUNDERSTORM POSSIBLE. ISOLATED WATERSPOUTS POSSIBLE. WAVES 2 FEET OR LESS BUILDING TO 2 TO 3 FEET. 850mb Temperature MSLP

15. Case Study #1 August 16, 2008 Through 12Z: SOUTHWEST WINDS 10 TO 20 KNOTS WAVES 2 TO 3 FEET. Waves below 2 ft Winds 10-15kts

16. Case Study #1 August 16, 2008 16Z: “What’s going on?” Winds estimated 15-20kts With waves near 3ft. VERY choppy waters A large no. of boats returning to harbor Through 16Z: SOUTHWEST WINDS 10 TO 20 KNOTS WAVES 2 TO 3 FEET. 3 TO 5 FEET SCA Waves below 2 ft Winds 12G18kts

17. Case Study #1 August 16, 2008 End result (22Z)/Verification SOUTHWEST WINDS eventually hit 20kts with gusts near 25kts WAVES approached 5ft.

18. (Warm Lake and Cold Airmass) (Cold Lake and Warm Airmass) Wind speed (10-20 kts) Small Craft Advisory (>= 4 ft/1.2m) End result (22Z)/Verification SOUTHWEST WINDS eventually hit 20kts with gusts near 25kts WAVES approached 5ft. Very close to 20kt Sensitivity study line

19. 1 st Important Conclusion Do not forecast 10-20kt wind forecasts when you have: –1) a long fetch –2) Winds to last several hrs –3) an unstable or marginally unstable Marine Boundary Layer. Rather – choose: –10-15kts (No SCA) or –15-20kts (SCA)

20. What’s the highest wave height observed in Lake Ontario? –(Buoy data available from: approx April-Nov 2002-2007 ) A) 15ft B) 20ft C) 25ft D) 30ft E) 35ft November 13, 2003 Wind: 24345G59KT 3AM Forecast: STORM WARNING 50KT STORMS WAVES 10-15 FEET Case Study #2 (Questionnaire….)

21. (Warm Lake and Cold Airmass) (Cold Lake and Warm Airmass) Wind speed (0-40 kts) Small Craft Advisory (>= 4 ft/1.2m) End result/Verification for highest wave heights On Lake Ontario (Apr-Nov 2002-2007) SOUTHWEST WIND 45kts with gusts to 59kts WAVES approached 25ft. Outside study area, But probably on target

22. The Remnants of Hurricane IKE passed right over Lake Ontario…. Sept 13, 2008 Sept 14, 2008 Sept 15, 2008 Case Study #3 Sept 15, 2008

23. 346AM and 1006AM update: SW WIND TO 30KTS WAVES 5-7 FT 341PM: W WIND TO 30KTS WAVES 4-6 FT 545PM: S TO W GALES TO 40KTS WAVES 4-7 FT 607PM GALES TO 35KTS WAVES 7-10FT 704PM GALES TO 40KTS WAVE 7-10FT 1007PM GALES TO 35KTS WAVES 7-10FT

24. Case Study #3 Sept 15, 2008 Verification: SOUTHWEST WINDS eventually hit 39kts with gusts to 50kts WAVES hit 12ft.

25. (Warm Lake and Cold Airmass) (Cold Lake and Warm Airmass) Wind speed (0-40 kts) Small Craft Advisory (>= 4 ft/1.2m) End result/Verification IKE WEST WINDS 39kts with gusts to 50kts WAVES hit 12ft. Sensitivity Study would Have over forecast wave Heights by several feet. But this was a unique case with short lived Wind event

26. Case Study #2 and #3 Why did we under forecast wave heights? Is it the formatter? What did the “Grids” show?

27. Stability Considerations Lighter winds have more of an impact on wave height when factoring in instability –3 “regimes” Moderate/Stronger winds – less impact when considering instability –2 “regimes” End State Wave Height (ft) Wind speed (10-20 kts)

28. Summary SCA Rule of thumb works: –Winds >18kts  Issue a SCA regardless of marine boundary layer –HOWEVER - SCA conditions possible for wind as low as 14kts –unstable marine boundary layer Forecasting 10-20kt winds can get you in trouble during summer/fall –Wave Heights can vary substantially (below or above SCA limits) within this range. Waves more susceptible to stability considerations for lighter winds.