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    Fig. 1.

    Heatwaves: (a),(c),(e),(g) 2-m temperature anomalies for the target week (indicated in the panel titles) from ERA5 data and (b),(d),(f),(h) those predicted by the ECMWF week-3 forecasts (hindcasts prior to 2016), with initialization dates indicated in panel titles. Rows show the (a),(b) California heatwave, (c),(d) European heatwave, (e),(f) U.S. heatwave, and (g),(h) East Asian heatwave. White boxes indicate the averaging areas used for Fig. 2. All case studies use model version CY45R1, except for the East Asia heatwave, which uses CY46R1.

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    Fig. 2.

    Heatwaves: PDF of the predicted 2-m temperature anomalies from the model ensemble averaged over the target week (indicated in Table 1) for the heatwave case studies, averaged over the white boxes in Fig. 1 and initialized at (from left to right) 4, 3, and 2 weeks before the start of the target week. Panels show the (a) California heatwave 2018, (b) European heatwave 2018, (c) southeastern U.S. heatwave 2019, and (d) East Asian heatwave 2013. Tercile limits (below normal: blue; normal: gray; above normal: red) are computed with respect to the lead time–dependent model climatology. Values above the 66th percentile (below the 33rd percentile) are represented by red (blue) shading. Gray shading represents values bet­ween these terciles. The yellow dots indicate the ensemble members that were used to construct the PDF (51 for forecasts, 11 for hindcasts). The extremes above the 90th (below the 10th) percentile are hatched and their probabilities are indicated by red (blue) numbers. The purple dashed line represents the anomaly in ERA5 averaged over the target week.

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    Fig. 3.

    As in Fig. 1, but for the cold spell case studies: (a),(b) Southeastern European cold spell in 2003 (model version CY46R1), (c),(d) central/northern European cold spell in 2018 (model version CY43R3), (e),(f) France cold spell in 2017 (model version CY43R1), and (g),(h) northern European cold spell in 2010 (model version CY46R1).

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    Fig. 4.

    As in Fig. 2, but for the cold spell case studies: (a) Southeastern European cold spell in 2003, (b) European cold spell in 2018, (c) France cold spell in 2017, and (d) the northern European cold spell in 2010.

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    Fig. 5.

    Precipitation events: Accumulated precipitation anomalies over the target week (week 3, indicated in the panel titles) for (a),(c),(e),(g) observations and (b),(d),(f),(h) the ECMWF model prediction (initialization date indicated in the panel titles). Rows show (a),(b) Guatemala, (c),(d) western Ecuador, (e),(f) northwestern Italy, and (g),(h) northeastern Australia. The blue boxes and dots indicate the target location for each case study, as indicated in Table 1. Observations are from (a),(c),(e) CPC and (g) AWAP.

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    Fig. 6.

    Precipitation extremes: Predictability scores for week 3, (a),(c),(e),(g) assessed through the area under the ROC curve for the above-normal category and (b),(d),(f),(h) Spearman’s rank correlation coefficient. The results were interpolated to the CPC unified grid. For details of the scores, see “Data and methods” section. Rows show (a),(b) ­Guatemala, (c),(d) western Ecuador, (e),(f) northwestern Italy, and (g),(h) northeastern Australia. The blue boxes and dots are as in Fig. 5.

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    Fig. 7.

    Cyclones: Satellite images at a time close to the maximum intensity of the storms for (a) Cyclone Claudia on 13 Jan 2020 (NOAA) (c) Cyclone Belna on 7 Dec 2019 (NASA), (e) Typhoon Chan-hom on 10 Jul 2015 (SSEC/CIMSS, University of Wisconsin–Madison), and (g) Medicane Zorbas (2018M02) on 29 Sep 2018 (MODIS NASA). (b),(d),(f),(h) Probability of cyclone occurrence for (b) Claudia initialized on 30 Dec 2019 for lead times of 15–21 days, (d) Belna initialized on 18 Nov 2019 for lead times of 22–28 days, (f) Chan-hom initialized on 15 Jun 2015 for lead times of 22–28 days, and (h) Medicane Zorbas initialized on 13 Sep 2018 for lead times of 0–32 days. Black lines indicate the observed cyclone tracks during the verification period, and the names of the cyclones corresponding to the tracks are indicated. The different choice of lead times for the case studies refers to the longest lead time for which the events were possible to be predicted.

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    Fig. 8.

    Cyclones: Outgoing longwave radiation (OLR) anomalies (shaded; W m−2) and MJO-filtered OLR anomalies (red contours; every 15 W m−2 for negative values) from (a),(c) observations averaged over (a) 0°–10°N and (c) 0°–10°S with tropical cyclone tracks (black lines) and names (first letter of the cyclone name in the red circle) and (b),(d) ECMWF ensemble forecasts initialized on 15 Jun 2015 and 18 Nov 2019. MJO filtering is performed using a wavenumber–frequency filter that selects for wavenumbers 0–9 and periods of 20–100 days. MJO-filtered OLR was calculated by padding the forecast with observations prior to initialization following the methodology described in Janiga et al. (2018). (e) CAPE (J kg−1) from the ECMWF ensemble forecast initialized on 30 Aug 2018 and valid on 26 Sep 2018.