ASSESSMENT OF THE NEW GREAT LAKES WATERSPOUT FORECAST SYSTEM

2013 Great Lakes Operational Meteorology Workshop

Victor Chung & Wade Szilagyi

Meteorological Service of Canada

April 9, 2013

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Introduction – The Great Lakes Waterspout Forecast System (GLWFS)

• Experimental tool → potential for waterspouts over the Great Lakes

• Output → Szilagyi Waterspout Index (SWI), 0-48 hrs

• Automation of the Waterspout Nomogram

• Used for the first time in 2012 at the OSPC

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Verification - Methodology

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Verification Considerations -Seasonal Period

• Peak of waterspout season (August - September) chosen

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Verification Considerations - Diurnal Time Period

• Daytime only (12-18Z, 18-24Z)

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Verification Considerations – Areal Coverage

• Half lake resolution (marine forecast sub-zones)

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Verification - Database

• 13,180 entries

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Verification - Database

• Date (Aug. – Sept.)

• Time (12-18Z, 18-24Z)

• Location (i.e. western Lake Erie)

• Forecast/Observed/Possible Waterspouts (Yes/No)

• Forecast SWI (<0, 0, 1,…,10)

• SWI Percent Coverage (0, 25, 50, 75,100%)

• Forecast/Observation Location Correlation (Yes/No)

• Lead Time (0-48 hrs)

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Verification - Results

• N = 1,318

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Verification - Results

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Verification - Results

• Average Lead Time = 36 hrs!

• Forecast/Observation Location Correlation = 92%

• Forecast SWI value-waterspout events most frequently associated with forecast SWI

≥ 7

• SWI Percent Coverage-over half of the events occurred when coverage was ≥ 75% →

SWI areal coverage is a factor to consider when forecasting waterspouts

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Case Study –Waterspout Outbreak (Aug. 9-13, 2012)

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1500Z, Aug 09, 2012

1604z

1601z

1542zA fewwaterspouts

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1800Z, Aug 09, 2012

1700z

1710zFunnels and 2 waterspouts

1700zA few waterspouts

1710-1735zMultiplewaterspouts 1926z

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2100Z, Aug 09, 2012

2145z

2137zMultiplewaterspouts

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0600Z, Aug 10, 2012

0524z

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1200Z, Aug 10, 2012

1242-1248z2 waterspouts

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0000Z, Aug 11, 2012

Early evening2 funnels

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1200Z, Aug 11, 2012

1330z

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1500Z, Aug 11, 2012

1630z

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2100Z, Aug 11, 2012

2000z

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0000Z, Aug 12, 2012

2325z

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1200Z, Aug 12, 2012

1510-1525z2+ waterspouts

1506z

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Conclusion

1.Has a very good lead time

2.Has excellent rare event skill score

3.Has good non-rare event skill scores

The Waterspout Forecast System:

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Future Work• Include surface convergence (SWI → ESWI)

• Higher resolution model output (horizontal and vertical)

• Distinguish between “Severe Wx” vs “Fair Wx” waterspouts

• Expand to other marine areas: Atlantic/Pacific coasts, globally

• Experimental → Operational

• Investigate use as a landspout forecast tool