the terrain

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Federal Department of Home Affairs FDHAFederal Office of Meteorology and Climatology MeteoSwiss

NWP Eumetcal course 26-29 November 2007 Langen – Germany Dean Gill

3-4 July 2007 missed heavy precipitation eventin the Western Swiss Alps(Or the art of forecasting precipitations in a mountainous region)

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The terrain

Geneva

Zurich

Locarno

Bern

Lausanne

Basel

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Heavy precipitation critical thresholds in Switzerland

50mm/24h

100mm/24h

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• Unseasonably strong westerly flow across the Alps.• Passage of an active frontal system in this rapid flow• Unusually active warm front and warm sector• cold front starting to wave against the Alps• Mainly large scale precipitations certainly with a convective

component (but no thunderstorms)

What happened?

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MeteoSwiss Surface analysis – 3 July 2007 12UTC

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UK Met Office Surface analysis – 4 July 2007 00UTC

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MeteoSwiss 500 hPa analysis – 3 July 2007 12UTC

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Western Switzerland

WV 5.35 - 7.15 µm 3 July – 18UTC

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WV 5.35 - 7.15 µm 4 July – 00UTC

Western Switzerland

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ECMWF 01.07.2007 00UTC run – 24h precip for 3 and 4 July

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Region receiving more than 50mm/12h

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Hourly Precipitation rate in Aigle, le Bouveret and le Moléson

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Consequences

• Floods• Landslides• Mudslides• Power outage• Fortunately no injuries or deaths!

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A new tool – MAP D-PHASE

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… and what about forecasting stratus cloud in mountainous regions?

the terrain

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