Deutscher Wetterdienst Zentrale Vorhersage DWD Workshop "Use and Verification of LEPS products",...

DWD Workshop "Use and Verification of LEPS products", Geneve, 26 - 28 May, 2003

Deutscher WetterdienstDeutscher WetterdienstZentrale Vorhersage

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Verification of LEPS products at the DWD - first results

Thomas Schumann, Deutscher Wetterdienst, Zentrale Vorhersage

D-63067 Offenbach, GermanyE-Mail: [email protected]



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Content

1. Introduction

2. A subjective verification method

3. Some case studies

4. Results

5. Conclusions and outlook



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1. IntroductionA lot of parameters and thresholds available ... at time steps H+24 . . . 120

Parameter Thresholds (> ... , Tn < ...)

fx 10 m/s 15 m/s 20 m/s 25 m/s

precip 24h 20 mm 50 mm 100 mm 150 mm

precip 72h 50 mm 100 mm 150 mm 250 mm

Tx 20°C 30°C 35°C 40°C

Tn < 5°C < 0°C < -5°C < -10°C

Selection for verification !



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2 Examples ...

Prob fx > 20 m/sMay 04, 12 + 24 ... 48 H

Prob Tx > 30°CMay 05, 12 + 18 ... 42 H



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Datenblatt zur Verifikation der LEPS-Vorhersagen

Datum Tmax Betroffene RegionZieltermin > 30 °C

Obs T+42 T+66 T+90 T+114

02.04.03 12 003.04.03 12 0 004.04.03 12 0 0 0 Südwesten (Obs)05.04.03 16 0 0 0 0 Südwesten (Obs)06.04.03 10 0 0 0 0 Rhein(Obs)07.04.03 8 0 0 0 0 Niederrhein(Obs)08.04.03 10 0 0 0 0 Freiburg(Obs)09.04.03 11 0 0 0 0 Südwesten (Obs)10.04.03 10 0 0 0 0 Bamberg(Obs)11.04.03 12 0 0 0 012.04.03 17 0 0 0 0 Rhein(Obs)13.04.03 20 0 0 0 0 Oberrhein(Obs)14.04.03 24 0 0 0 30 Oberrhein(114),Oberrhein(Obs)15.04.03 26 0 0 0 0 Niederrhein(Obs)16.04.03 25 0 40 40 0 Rhein(90),Oberrhein17.04.03 24 50 60 20 40 Westen(114),Westen(90),Südwesten, Stellenweise am Rhein(42)18.04.03 21 0 0 0 20 Westen(114)

2. A subjective verification method

Permanent Verification (Excel-Sheet) or Case Studies ...



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Problem: Lack of severe events (permanent blocking)a few cases only

SLP Analysis, May 05, 06 UTCPrecipitation Anomaly 2003Dresden and Duesseldorf(www.cpc.ncep.noaa.gov)



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3. Some case studies3.1. Temperature - late cold outbreaks Date: April 09/10 and 10/11, 2003

ECM April 7, 12 + 72 h, SLP (blue) and T850 (red) ECM April 8, 12 + 72 h

L

L

H

H

H



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Tn forecasts 09/10 AprilApril 08, 12 + 18 ... 42 H (left top), April 07, 12 + 42 ... 66 H (left bottom)

Tn forecast 10/11 AprilApril 06, 12 + 66 ... 90 H



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EPS ECMWF Prob Tmin < 0°C April 10/11April 06, 12 + 72 ... 84 H

April 08, 12 + 18 ... 42 H



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Observed Tn April 10, 06 UTC

Observed Tn April 11, 06 UTC

Late frost over widespread areas



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... The snow forecast has been performed well ... (excerpt Southern Germany)

April 07, 12 + 72 ... 96 H April 11, 06 UTC 24-hr snow amount (cm)

April 09, 12 + 24 ... 48 H



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EPS ECMWF prob snow > 1 cmApril 09, 12 + 24 ... 48 H

Snow fc fromthe EPS:

No signal !



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3.2. Temperature - daily Temperature Maximum

ECM March 22, 12 + 72 h, SLP (blue) and T850 (red)

Date: March 25, 2003Tmax exceeding 20°C over SouthernGermany is likely

H

Observed Tmax



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March 24, 12 + 18 ... 42 H (left top), March 23, 12 + 42 ... 66 H (left bottom)

March 21, 12 + 90 ... 114 H (right)

Forecasts perform well, even the effect oflarge cities (London) is visible !

Useful forecasts also in similar situations !



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3.3. Total precipitation, accumulated over 24 hours

ECM April 1, 12 + 72 h, SLP (blue) and T850 (red)

Case: April 03/04, 2003

large-scale precip at thenorthern side of the Alpsand the Pyrenees

mostly convective precipat the Algerian coast andthe Croatic and Slowenicmountains

L

L

L

H



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Obs 24-hr precip values, April 4, 06 UTC (top)and April 5, 06 UTC (right)

Gaps caused bycountries, doesn´treport 24-hr preciptotals

a better verification ifLEPS could predict12-hr precip totals at06 and 18 UTC (synop)



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March 31, 12 + 72...96 H April 1, 12 + 48...72 H

April 1, 12 + 72...96 H March 31, 12 + 96...120 H

LEPS fc valid forApril 4 (top)threshold: 20 mm

LEPS fc valid forApril 5 (bottom)threshold: 50 mm



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3.4. Wind gustsDate: April 05/06, 2003

MSLP Analysis April 05, 12 UTC

• Through situation, in transistion to a cut-off over eastern Europe• instable conditions over eastern Germany and Poland ---> gusts

April 06, 12 UTC



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Max wind gusts (obs) April 05, 18 UTC

gusts up to 24 m/sover northeasternparts of Germany and the North Seacoast

April 03, 12+24...48 HThreshold: 20 m/s

Excellent Forecast



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Max wind gusts (obs) April 07, 00 UTC

gusts up to 24 m/snear the Baltic Seacoast

April 03, 12 + 48...72 HThreshold: 20 m/s

Gusts overestimated !



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EPS ECMWF prob fx > 20 m/sApril 03, 12 + 48 ... 60 H,valid at April 05, 12 ... 24 UTC

April 04, 12 + 48 ... 60 Hvalid at April 06, 12 ... 24 UTC



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April 19, 12 UTC Sat picture (vis) andGeopotential 500hPa ECM 12 + 00 h

Small cut-off low over central Germany

caused convectiveprecipitation up to32 mm (10460)

3.5. Convective precipitation eventsCase study: April 19 - cut-off low



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Obs April 19, 18 UTCweather, lightning,radar

Obs April 20, 06 UTC24-hr precip totals



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24-hr Precip totals (right)April 19, 00 UTC, GME + 24 h April 18, 12 UTC, ECM + 36 hBoth models gave valuable signals !

LEPS April 18, 12 UTC + 24...48 hNo signal !



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EPS ECMWF prob precip_24hr > 10mmApril 18, 12 + 24 ... 48 H

ECMWF T511 precip_24hrApril 16, 12 + 66 ... 90 H (left)April 18, 12 + 18 ... 42 H (right)valid April 19/20, 06 UTC

T511-forecast: event was predictedquite well, but the EPS: No signal



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4. Results

• preliminary status - experiences obtained from several forecasters during semi-operational use

• Case studies ...

• Subjective verification method takes a lot of time ...

• High expectations to the LEPS• well-known problems of the LM- and the ECMWF (EPS- and T511)-forecasts (wind gusts, convective precipitations)



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Parameter Results Comments

Minimum temperature No signal Don´t use the LEPS !Maximum temperature fair, useful realistic regional assignment of

the signals, some skill in med-range

Wind gusts fair, useful gusts sometimes overestimated (LM)realistic presentation of orographiceffects, without skill in med-range

Snow not very well realistic presentation of orographiceffects, one case study only

precipitationlarge scale fair, useful realistic regional assignment of the

signals, rapid lost of predictabilityby increasing leading time

convective mostly no The use if LEPS is not signal recommendable !



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5. Conclusions and outlook• LEPS wasn´t able to meet our expectations (no skill in med-range)

• predictions of convective precipitations and gusts, caused by convective events, not useful

• forecasts of late cold outbreaks: results very poor, no signal

• Acceptance by forecasters

Results of this workshopexperiences from otherCOSMO-LEPS members

Further development ofthe LEPS systemSimulation of „historic“extreme weather events

Continuing verification ?Continuous or case-sensitive ?

Improvements of the LEPSforecasts in the near future ?

Enhanced operational use of the LEPS system by forecaters ?



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Thank you for your attention !

Deutscher Wetterdienst Zentrale Vorhersage DWD Workshop "Use and Verification of LEPS products",...

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Transcript of Deutscher Wetterdienst Zentrale Vorhersage DWD Workshop "Use and Verification of LEPS products",...