Files containing data in Figures 1-7 in the manuscript Korhonen N. et al. "The probabilistic skill of Extended-Range Heat wave forecasts over Europe". Files and their contents: Fig1a_HW_lower_threshold_ERA5_all_years.nc Data of Fig1a: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2019 of the ERA5 reanalyses (Hersbach, et al. 2020). Fig1b_HW_lower_threshold_ERA5_excl2010.nc Data of Fig1b: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2009 and 2011-2019 of the ERA5 reanalyses (Hersbach, et al. 2020). Fig1d_HW_lower_threshold_EC_fc_1wk_all_years.nc Data of Fig1d: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2019 of the ensembles of the extended range hindcasts of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS; Cycles 46r1 and 47r1; Vitart, 2014) in forecast week 1. Fig1e_HW_lower_threshold_EC_fc_1wk_excl2010.nc Data of Fig1e: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2009 and 2011-2019 of the ensembles of the extended range hindcasts of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS; Cycles 46r1 and 47r1; Vitart, 2014) in forecast week 1. Fig1g_HW_lower_threshold_EC_fc_2wk_all_years.nc Data of Fig1g: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2019 of the ensembles of the ECMWF’s hindcasts in forecast week 2. Fig1h_HW_lower_threshold_EC_fc_2wk_excl2010.nc Data of Fig1h: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2009 and 2011-2019 of the ensembles of the ECMWF’s hindcasts in forecast week 2. Fig1j_HW_lower_threshold_EC_fc_3wk_all_years.nc Data of Fig1j: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2019 of the ensembles of the ECMWF’s hindcasts in forecast week 3. Fig1k_HW_lower_threshold_EC_fc_3wk_excl2010.nc Data of Fig1k: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2009 and 2011-2019 of the ensembles of the ECMWF’s hindcasts in forecast week 3. Fig1m_HW_lower_threshold_EC_fc_4wk_all_years.nc Data of Fig1m: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2019 of the ensembles of the ECMWF’s hindcasts in forecast week 4. Fig1n_HW_lower_threshold_EC_fc_4wk_excl2010.nc Data of Fig1n: The lower thresholds of heat wave days: the 90th percentile of the 5-day moving average temperature in summers 2000-2009 and 2011-2019 of the ensembles of the ECMWF’s hindcasts in forecast week 4. Fig2a_LHWMD_ERA5.nc Data of Fig2a: The duration of the longest period of heat wave days in each grid point over Europe defined from the ERA5 reanalysis data of summers 2000-2019. Fig2b_LHWMD_ERA5.nc Data of Fig2b: The duration of the longest period of heat wave days in each grid point over Europe defined from the ERA5 reanalysis data of summers 2000-2009 and 2011-2019. Fig2c_HWNP_ERA5.nc Data of Fig2c: the number of periods with heat wave days in the ERA5 reanalyses during 2000-2019. Fig2d_HWNP_ERA5.nc Data of Fig2d: the number of periods with heat wave days in the ERA5 reanalyses during 2000-2009 and 2011-2019. Fig3a_sharpness_diagram.txt Data of the sharpness diagram in Fig. 3a. Fig3b_reliability_diagram.txt Data of the reliability diagram in Fig. 3b. Fig4a_BSS_Week1_All_hindcasts.nc Fig4b_BSS_Week1_excluding_longest_HW.nc Fig4c_BSS_Week1_excl2010.nc Fig4d_BSS_Week2_All_hindcasts.nc Fig4e_BSS_Week2_excluding_longest_HW.nc Fig4f_BSS_Week2_excl2010.nc Fig4g_BSS_Week3_All_hindcasts.nc Fig4h_BSS_Week3_excluding_longest_HW.nc Fig4i_BSS_Week3_excl2010.nc Fig4j_BSS_Week4_All_hindcasts.nc Fig4k_BSS_Week4_excluding_longest_HW.nc Fig4l_BSS_Week4_excl2010.nc Data of the BSS in Figures 4a-l. Figure5a_ForecastWeek1.txt Figure5b_ForecastWeek2.txt Figure5c_ForecastWeek3.txt Figure5d_ForecastWeek4.txt Data of the boxplots in Figures 5a-d. Figure6a_ForecastWeek1.txt Figure6b_ForecastWeek2.txt Figure6c_ForecastWeek3.txt Figure6d_ForecastWeek4.txt Data of the boxplots in Figures 6a-d. Figure7a_ForecastWeek1.txt Figure7b_ForecastWeek2.txt Figure7c_ForecastWeek3.txt Figure7d_ForecastWeek4.txt Data of the boxplots in Figures 7a-d. Hersbach, H., Bell, B., Berrisford, P., et al.: The ERA5 Global Reanalysis, Quart. J. Roy. Meteor. Soc., 146, 1999-2049, doi:10.1002/qj.3803, 2020. Vitart F.: Evolution of ECMWF sub-seasonal forecast skill scores, Q. J. R. Meteorol. Soc., 140, 1889–1899, doi: 10.1002/qj.2256, 2014.

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