Page 1 © Crown copyright 2005 ECMWF User Meeting, June 2006 Developments in the Use of Short and Medium-Range Ensembles at the Met Office Ken Mylne Ensemble Forecasting Manager

Page 2 © Crown copyright 2005 ECMWF User Meeting, June 2006 Contents First Guess Early Warnings – again! Example of EPS Use for Confidence New Applications of EPS Drought-planning Forecasts Best-Member Project Eurorisk PREVIEW Windstorms MOGREPS – The new Met Office short-range ensemble

First Guess Early Warnings - A confession

Page 4 © Crown copyright 2005 ECMWF User Meeting, June 2006 FGEW Verification – an error Over the last few years we have reported on verification results from our First Guess Early Warnings A key feature was a maximum in skill at 4 days Much discussion and investigation With regret and apologies, I have to report that this result was caused by an error in our verification scheme Misalignment of forecast times with verifying times in the verification database Day 4 was correctly aligned, other days wrong

Page 5 © Crown copyright 2005 ECMWF User Meeting, June 2006 Corrected Verification - ROC With the bug corrected the verification shows a near- constant ROC area for days 1-4 of the forecast with a slow decline from day 5 or 6.

Page 6 © Crown copyright 2005 ECMWF User Meeting, June 2006 Corrected Verification - Reliability Reliability diagrams show useful resolution at 2 and 4 days.

Page 7 © Crown copyright 2005 ECMWF User Meeting, June 2006 Corrected Verification – Cost-loss Cost-loss curves show slow reduction in values at longer lead times Largest effect for large C/L ratios Increasing chance of capturing event at high probability

Example of EPS Use for Confidence

Page 9 © Crown copyright 2005 ECMWF User Meeting, June 2006 Example – low spread, high confidence Cold period in November 06 with snow in SW ECMWF EPS gave very high confidence of blocking breakdown Allowed issue of high confidence of return to mild conditions on Wed 30 th 5 days ahead Analysis of 0600 on 30 th confirms this was correct

New Applications of EPS - i) Drought Planning Forecasts

Page 11 © Crown copyright 2005 ECMWF User Meeting, June 2006 Drought planning forecasts Probabilities for 10-day rainfall totals Mod-High probability of below normal Only low risk of very dry (<5mm in 10 days) in SE England

New Applications of EPS - ii) Best Member Project

Page 13 © Crown copyright 2005 ECMWF User Meeting, June 2006 Integrating Ensembles into Operations We would like to make all forecasts probabilistic BUT Met Office customers still demand a best-estimate deterministic forecast Currently use field modification Link UK GM at T+36 with preferred solution later Can we choose an ensemble Best Member? Best fit to preferred solution, or Ensemble Mean? Representative member of largest cluster? Best Member could give: Dynamically consistent forecast at all times Full set of consistent model fields

Page 14 © Crown copyright 2005 ECMWF User Meeting, June 2006 Best Member project Project being run with Operations Centre to test: Can we identify a suitable Best Member? How long does a good EPS member stay good? Can we re-calculate probabilities? Expect BM selected for mesoscale may be different from that for synoptic scale/medium range forecasts. Use error tracking to identify source regions Consider short and medium ranges separately, using MOGREPS and EC EPS respectively.

New Applications of EPS - iii) Eurorisk PREVIEW Windstorms

Page 16 © Crown copyright 2005 ECMWF User Meeting, June 2006 Ensemble Forecasts PEACE (MeteoFrance) SRNWP-PEPS (DWD) LAMEPS (Met.no) ECMWF EPS (ECMWF) MOGREPS ( Met Office UK) COSMO-LEPS Eurorisk PREVIEW Windstorms Database (Met Office UK) Kalman Filter Wind Gust Calculation (Meteo-France) Windstorm Forecast Products Website (Met Office UK) Risk Mapping Data (SMHI) Windstorm Risk Mapping Products Multi-model ensemble forecasts for Windstorm Risk Adapted existing site-specific database tables for additional ensembles 196 sites across 9 countries

Page 17 © Crown copyright 2005 ECMWF User Meeting, June 2006 Products Traffic light maps for initial alerts Site-specific details: Meteograms Wind-roses Eurorisk PREVIEW Windstorms

Page 18 © Crown copyright 2005 ECMWF User Meeting, June 2006 Eurorisk PREVIEW Windstorms Alert thresholds will be a combination of probability and severity, eg. Severity (Climate Percentile) 90%95%99%99.9% Prob>80% 50-80% 20-50% 1-20% Thresholds referenced to site climates Analysed from ERA40 Calibrated using site observations

MOGREPS – Met Office Global and Regional EPS

Page 20 © Crown copyright 2005 ECMWF User Meeting, June 2006 MOGREPS – The Met Office short-range Ensemble Ensemble designed for short-range Regional ensemble over N. Atlantic and Europe (NAE) Nested within global ensemble ETKF perturbations Stochastic physics T+72 global, T+36 regional Aim to assess uncertainty in short-range, eg.: Rapid cyclogenesis Local details (wind etc) Precipitation Fog and cloud NAE MOGREPS is on Operational Trial for 1 year from September 2005

Page 21 © Crown copyright 2005 NWP Seminar 3 rd Feb 2006 T+12 perturbed forecast T+12 ensemble mean forecast ( - ) + = Transform matrix Control analysis Perturbed analysis 0.9 Pert Pert Pert Pert Pert 5 Ensemble Transform Kalman Filter (ETKF)

Page 22 © Crown copyright 2005 NWP Seminar 3 rd Feb 2006 Stochastic Convective Vorticity (SCV) Unresolved impact of organised convection (MCSs) Not used in the higher resolution regional ensemble Random Parameters (RP) Structural error due to tuneable parameters Stochastic Kinetic Energy Backscatter (SKEB) Similar to ECMWF CASBS scheme Excess dissipation of energy at small scales SKEB implemented in global ensemble in PS11 Stochastic schemes for the UM Impact is propagated to next cycle through the ETKF!

Page 23 © Crown copyright 2005 ECMWF User Meeting, June 2006 Display system

Page 24 © Crown copyright 2005 ECMWF User Meeting, June 2006 Products – Postage stamps

Page 25 © Crown copyright 2005 ECMWF User Meeting, June 2006 Products – Probability charts

Page 26 © Crown copyright 2005 ECMWF User Meeting, June 2006 MOGREPS Site-specific forecasts EPS Meteograms MOGREPS Plume Kalman filter MOS is being implemented for MOGREPS forecasts

Page 27 © Crown copyright 2005 NWP Seminar 3 rd Feb 2006 Verification Verification to date is very basic Verification is being implemented within the Area-based Verification system (ABV) and Site-specific Verification system (SBV) Verification performed over NAE area for forecasts from global ensemble Performed (except where stated) against analysis For 111 cycles between 17/10/05 and 9/1/06

Page 28 © Crown copyright 2005 NWP Seminar 3 rd Feb hPa height – spread and RMSE Spread optimised by variable inflation factor against observations in u, v, T and RH at T+12 Appears too large because verified against analysis (tbc) Ensemble mean skill does not currently improve on control skill Spread and RMSE for 500hPa GPH

Page 29 © Crown copyright 2005 NWP Seminar 3 rd Feb hPa height – rank histogram Rank histogram is encouragingly flat Close to ideal Suggests that ETKF perturbations are representative of genuine analysis errors This performance seems much improved on ECMWF ensemble Rank Histogram at T+72 for 500hPa GPH Solid – operational, Dotted – PS11 upgrade

Page 30 © Crown copyright 2005 ECMWF User Meeting, June 2006 Verification - T+36 6hr total > 0.5mm Global EnsembleRegional Ensemble

Page 31 © Crown copyright 2005 ECMWF User Meeting, June 2006 Verification - T+36 6hr total > 5mm Global EnsembleRegional Ensemble

Page 32 © Crown copyright 2005 ECMWF User Meeting, June 2006 Verification - T+36 6hr total > 0.5mm Global Ensemble GlobalRegional

Page 33 © Crown copyright 2005 ECMWF User Meeting, June 2006 Conclusions FGEW verification resolved! EPS continues to become more integrated in forecasting procedures First-choice for new services (eg drought planning) How to produce best deterministic forecast? Basis of new risk-management services for EU MOGREPS provides a promising new short- range ensemble capability complements EPS for medium-range

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