ECMWF Forecasts Laura Ferranti, Frederic Vitart and Fernando Prates

Predictability of Atlantic weather regimes for medium forecast ranges

ECMWF ODRD meeting DRD meeting, 2 July 2004 Daily Time series of the four Euro-Atlantic weather regimes: analysis and EPS scenarios at t+7days NAO+ Blocking NAO- Atl. Ridge November 2011December 2011January 2012February 2012 Z500 Monthly mean anomalies from analysis: Analysis

Wind Storm 2-3 January 2012 ECMWF ANALYSIS Mslp & Winds 250hPa (kt) “...this storm was judged as the most severe for 13 years – since 26 December 1998” (south Scotland) MetOffice

SJ Metosat IR Ch 7 VT: 03Jan UTC ANALYSIS: System-Relative wind speed & Equiv Pot temperature ~ 850 hPa VT: 03Jan UTC Analysis: Earth-Relative wind speed (m/s). θ (c. every 2 k) and Q (g/kg)

EPS -Extreme Forecast Index 10fg Z1000 hPa EM CDFs for the EPS & M-climate (black) (24-48h) Glasgow airport VT: h +72h +144h Obs at 0820 UTC

+72 VT: 04 Jan 00 UTC Probability that gusts exceed 5-year return value +48 VT: 04 Jan 00 UTC Probability that gusts exceed 5-year return value Probability that Gusts exceed 10-year return value

Monthly forecast performance for DJF 2012

Predictions of the cold wave in February: onset 23-29/01/ /01/201230/01-05/ /02/2012 Verifying anomalies Forecast day12-18 Forecast day19-25

Predictability of the Cold event in Feb 2012 Sensitivity experiments to investigate the sources of predictability of the cold event in February: 51 member 32-day T255L91 coupled from day 0 for 2 starting dates 5 th and 9 th Jan 2012 : - Control experiment - IFS forced by observed SST/Sea Ice - Stratosphere relaxed to operational analysis - Tropics (20N-20S) relaxed to operational analysis

IFS forced by observed SST and sea-ice 2-metre temperature anomalies Forecast day Start date: 05/01 Stratosphere relaxed to analysis Tropics relaxed to analysis 30/01-05/ Verifying anomalies

NW Iberian Peninsula PPN time series ( normal )

12-18/12/ /12/ /12/201126/12-01/01/2012 Verifying anomalies Forecast day12-18 Forecast day19-25

09-15/01/ /01/ /01/ /01/2012 Verifying anomalies Forecast day12-18 Forecast day19-25

06-12/02/201230/01-05/02/ /02/ /02/2012 Verifying anomalies Forecast day12-18 Forecast day19-25

Conclusions: “The most severe storm for 13 years” in Scotland was well predicted 3-2 days in advance by the EPS. The Extreme Forecast Index (EFI) and probabilities for very unusual wind gusts thresholds provided reliable information at this forecast time range. The onset of the cold event in February was well predicted at day while its demise was persisted for a further week. Sensitivity experiments indicate that the larger contribution to the cold Feb conditions over Western Europe is associated with tropical variability. The persistence of dry-than-normal conditions was well predicted at day in SW Europe for December and January but poor during late January and February.

ECMWF ODRD meeting DRD meeting, 2 July 2004 Seasonal forecast performance for DJF 2012

ECMWF ODRD meeting DRD meeting, 2 July 2004 NINO 3.4 past predictions

ECMWF ODRD meeting DRD meeting, 2 July mt predictions for DJF 2012: init.date:1Nov2011 Verifying anomalies ECMWF Ens. Mean anomalies EUROSIP Ens. Mean anomaliesAGCM forced by SST (S3)

ECMWF ODRD meeting DRD meeting, 2 July 2004 Verifying anomalies DJF 2012 Z500 Predictions for DJF 2012: Init.date:1Nov2011 ECMWF Ens. Mean Anom. EUROSIP Ens. Mean Anom.

ECMWF ODRD meeting DRD meeting, 2 July 2004 Z500 Predictions for DJF 2012 Init.date:1Nov2011 Nov 2011Dec Jan 2012Jan –Feb 2012 ECMWF Ens. M. anom : Verifying anomalies:

ECMWF ODRD meeting DRD meeting, 2 July 2004 Dec 2011JF 2012 Z500 Predictions for DJF 2012 Init. date: 1 Dec 2011 Verifying anomalies: ECMWF Ens. M. anom :

ECMWF ODRD meeting DRD meeting, 2 July 2004 Anomaly correlations of forecasts initiated with four Atlantic regimes: Thanks to Martin Janousek All forecast in the seasons Nov- April Nov-March 2012

ECMWF ODRD meeting DRD meeting, 2 July 2004 RMSE/sda Thanks to Martin Janousek >17days Persistence distribution

ECMWF ODRD meeting DRD meeting, 2 July 2004 Predictive skill of the Euro-Atlantic regimes in the monthly forecast Brier Skill Scores : Forecast Range All regimesNAO+BlockingNAO-Atl. Ridge 1-7 days days days days days days days days days Red values are the BSS from the persisting the preceding week Blue values are the BSS from System 3 [ From Susanna Corti] Forecast Range All regimesNAO+BlockingNAO-Atl. Ridge 1-7 days days days days days days days days days

ECMWF ODRD meeting DRD meeting, 2 July 2004 Conclusions: Overall the temperature anomalies for DJF were well predicted by the seasonal forecast. ECMWF and Eurosip systems overestimated the teleconnections associated with La Niña. The onset of the cold event in February was well predicted at day while its demise was persisted for a further week. Sensitivity experiments indicate that the larger contribution to the cold Feb conditions over Western Europe is associated with tropical variability. An experiment with an ocean mixed layer show a further cooling in SST and 2m temp for the cold event in Feb..

ECMWF ODRD meeting DRD meeting, 2 July 2004 Conclusions: There is skill in predicting the Euro-Atlantic weather regimes up to day in the monthly forecast and up to month 1 in the seasonal forecast. Sys4 skill is improved with respect to Sys3 for all the regimes. Flow dependent scores indicate that forecast initiated in blocking conditions have less skill than the forecast initiated in NAO- conditions. Further assessment is in progress.