Page 1 © Crown copyright 2005 ECMWF User Meeting, 14-16 June 2006 Developments in the Use of Short and Medium-Range Ensembles at the Met Office Ken Mylne.

© Crown copyright 2005 ECMWF User Meeting, 14-16 June 2006 Page 1

Developments in the Use of Short and Medium-Range Ensembles at the Met Office

Ken Mylne

Ensemble Forecasting Manager


Contents

First Guess Early Warnings – again!

Example of EPS Use for Confidence

New Applications of EPSDrought-planning ForecastsBest-Member ProjectEurorisk PREVIEW Windstorms

MOGREPS – The new Met Office short-range ensemble

First Guess Early Warnings- A confession


FGEW Verification – an error

Over the last few years we have reported on verification results from our First Guess Early WarningsA key feature was a maximum in skill at 4 days

Much discussion and investigationWith regret and apologies, I have to report that this

“result” was caused by an error in our verification schemeMisalignment of forecast times with verifying

times in the verification databaseDay 4 was correctly aligned, other days wrong


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.


Corrected Verification - Reliability

Reliability diagrams show useful resolution at 2 and 4 days.


Corrected Verification – Cost-loss

Cost-loss curves show slow reduction in values at longer lead timesLargest effect for large C/L ratios

Increasing chance of capturing event at high probability

Example of EPS Use for Confidence


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 30th 5 days aheadAnalysis of 0600 on 30th confirms this was correct

New Applications of EPS - i) Drought Planning Forecasts


Drought planning forecasts

Probabilities for 10-day rainfall totals

Mod-High probability of below normalOnly low risk of very dry (<5mm in 10 days) in SE England

New Applications of EPS - ii) “Best Member” Project


Integrating Ensembles into Operations

We would like to make all forecasts probabilisticBUT Met Office customers still demand a best-estimate deterministic forecastCurrently use field modification

Link UK GM at T+36 with preferred solution laterCan 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 timesFull set of consistent model fields


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


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


Products Traffic light maps for initial alerts Site-specific details:

Meteograms Wind-roses




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 climatesAnalysed from ERA40Calibrated using site observations

MOGREPS – Met Office Global and Regional EPS


MOGREPS – The Met Office short-range Ensemble

Ensemble designed for short-rangeRegional ensemble over N. Atlantic and Europe (NAE)Nested within global ensembleETKF perturbationsStochastic physicsT+72 global, T+36 regionalAim 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 3rd Feb 2006

T+12 perturbed forecast

T+12 ensemble mean forecast

( - ) + =

( - ) + =

( - ) + =

( - ) + =

( - ) + =Transform matrix

Control analysis

Perturbed analysis

0.9 Pert 1-0.1 Pert 2-0.1 Pert 3-0.1 Pert 4-0.1 Pert 5

Ensemble Transform Kalman Filter (ETKF)


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 schemeExcess dissipation of energy at small scalesSKEB implemented in global ensemble in PS11

Stochastic schemes for the UM

Impact is propagated to next cycle through the ETKF!


Display system


Products – Postage stamps


Products – Probability charts


MOGREPS Site-specific forecasts

EPS Meteograms

MOGREPS Plume

Kalman filter MOS is being implemented for MOGREPS forecasts


Verification

Verification to date is very basicVerification 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


500hPa 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


500hPa height – rank histogram

Rank histogram is encouragingly flatClose 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


Verification - T+36 6hr total > 0.5mm

Global Ensemble Regional Ensemble


Verification - T+36 6hr total > 5mm

Global Ensemble Regional Ensemble


Verification - T+36 6hr total > 0.5mm

Global Ensemble

Global Regional

0.84 0.88


Conclusions

FGEW verification resolved!

EPS continues to become more integrated in forecasting proceduresFirst-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

Any questions?

Page 1 © Crown copyright 2005 ECMWF User Meeting, 14-16 June 2006 Developments in the Use of Short and Medium-Range Ensembles at the Met Office Ken Mylne.

Documents

crown copyright

ecmwf user meeting

verification verification

confidence slide

confession slide

correct slide

regional eps slide

high probability slide