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Forecasting severe convective hazards

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-2: As Fig8.1.9.6-1 but with ensemble control precipitation totals over 9hrs added: purple > 10mm.  In practice, the fact that there is precipitation indicates sufficient availability of moisture while the very high EFI indicates that unusual (i.e. climatologically high as defined by M-climate) convective available potential energy (MUCAPE) is available in the north Germany area.  Precipitation totals in the very active storms that are likely to form will be greater than ensemble control or ensemble members show (here ensemble control precipitation) and with associated significant downdraught gusts.  

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-4: CAPE-shear EFI, data time 00UTC 22 June 2017, valid for 00-24UTC 22 June 2013 (as on Fig8.1.9.6-3).  EFI colours orange and red taken as indicating an extreme event likely.  SOT values indicate the ratio of departures of ENS forecast values from the M-climate extreme considering the greatest 10% ENS members.  The other charts show MUCAPE-shear values in the M-climate (derived on 19 June 2017) wherein only 1 in 10 occasions (central chart) and only 1 in 100 occasions realises more than the values shown.  The existence of significant EFI and SOT, even some days in advance, should not be overlooked, particularly if the actual forecast MUCAPE-shear values are much greater than the M-climate values (at say the 90th or 99th percentiles) for the area.

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All the charts below correspond to the same example. All are for data time 00UTC 6th August 2017, and we focus on the forecast for 8th August.  Fig8.1.9.6-7 and Fig8.1.9.6-8 show 6-hour ensemble control precipitation forecasts for 00UTC on the 8 and 9 Aug 2017 as displayed by ecCharts.  It appears an area of significant rainfall associated with an upper trough moves from southwest France to Austria.   However, precipitation data is not shown for 12UTC on 8 Aug.  Meanwhile 24-hour total precipitation EFI (0.9) (Fig8.1.9.6-9) and MUCAPE-shear EFI (0.85) (Fig8.1.9.6-11) are available for 00UTC 9 Aug and show very high values.  MUCAPE EFI (0.6) (Fig8.1.9.6-10)  is only moderate illustrating the significant impact of bulk shear to give the high MUCAPE-shear EFI values.  The precipitation meteogram for the western Alps shows heavy rainfall in that area during the day and this is confirmed by data on Fig8.1.9.6-8 and Fig8.1.9.6-12 (note that these charts have different but overlapping validity periods). 

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.  The examples below may be used as a guide to performance of the Ensemble Control Forecast (ex-HRES).

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Fig8.1.9.6-7: ecChart showing 300hPa height with stratiform and convective rainfall (convective rainfall is plotted on top of stratiform) over the last 6 hr for T+48hr verifying at 00UTC 08 Aug 2017 based on ensemble control data time 00UTC 6 August 2017.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-8: ecChart showing 300hPa height with stratiform and convective rainfall over the last 6 hr for T+72hr verifying at 00UTC 09 Aug 2017 based on ensemble control data time 00UTC 6 August 2017.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-9: ecChart showing 300hPa height with total precipitation EFI at T+72hr verifying at 00UTC 09 Aug 2017 based on ENS data time 00UTC 6 August 2017.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-10: ecChart showing 300hPa height with CAPE EFI for the 24h ending at 00UTC 09 Aug 2017 based on ENS data time 00UTC 6 August 2017.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-11: ecChart showing 300hPa height with CAPE Shear EFI for the 24h ending at 00UTC 09 Aug 2017 based on ENS data time 00UTC 6 August 2017.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-12: ECMWF chart showing stratiform and convective rainfall over the last 6 hr for T+60hr verifying at 12UTC 08 Aug 2017 based on ensemble control data time 00UTC 6 August 2017. Also shown are surface isobars.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-13: ecChart showing the probability of precipitation ≥20mm in 24hrs ending 18UTC 9 August 2017. The forecast probability of heavy rainfall is concentrated at about 6ºE, in amongst the forecast CAPE-shear EFI maxima in Fig8.1.9.6.12.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-14:  15day meteogram with M-climate for 45N06E based on ENS data time 00UTC 6 August 2017.  An exceptional event is forecast for 8 Aug; the median lies above the 99th percentile of M-climate (green line).  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-15: CDF and associated EFI for west Alps region (45N06E).  Forecasts with a data time of 00UTC 6th, as on the other plots above, are denoted by the darkest of the two dashed blue lines.  There is a consistently high EFI for rainfall (over 80%) which is sufficient for forecasting a significant and maybe an extreme rainfall event.  Some ENS members show rainfall totals close to the M-climate maxima.  The slope of the precipitation CDF shows the variation within ENS members, but all members show greater than M-climate values.  For greater confidence the slope of the CDF should be more vertical.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-16: Probability of Detection and False Alarm Ratio results from an initial investigation on the ability of HRES in capture of MCS.  

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

Fig8.1.9.6-17:  ROCA Diagram showing  Relative Operating Characteristics (ROCA) diagrams can show skill of CAPE and CAPE-shear Extreme Forecast Index (EFI) at recognising severe convective outbreaks outbreaks (verified against observed MCS).  The area under the Relative Operating Characteristics (the ROCA ) curve gives an indication of skill (1.0 = High Skill; 0.5 = No Skill).  The EFI is verified against severe weather reports in the European Severe Weather Database (ESWD) averaged over the April-September periods between 2017 and 2020.  

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-18: Comparison between HRES (9km resolution) output and observed distribution of MCS areas over Europe.  HRES data time 23 June 2021 12UTC, Verifying time 24 June 2021 00UTC. Observe MCSs are persisting during the night.

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-19: Forecast vertical profile for Zaragoza DT 00UTC 6 July 2023 VT 12UTC 6 July 2023.  Large MUCAPE can be released after overcoming small CIN with strong bulk wind shear available.  The ENS cumulative distribution function for precipitation at Zaragoza during the 24hr period 00UTC 6 July to 00UTC 7 July 2023.  The CDFs for DT 00UTC 5 July (purple), DT 12UTC 5 July (blue), DT 00UTC 6 July (red) all show about 5% of ensemble members produce precipitation greater than the extreme of M-climate for Zaragoza.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-21: Forecast Extreme Forecast Index for CAPE with Shift of Tails for 24hrs to VT 00UTC 27 Dec 2023, DT 00UTC 26 Dec 2023.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-22: Forecast Extreme Forecast Index for CAPE-shear with Shift of Tails for 24hrs to VT 00UTC 27 Dec 2023, DT 00UTC 26 Dec 2023.  Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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Fig8.1.9.6-24: Observed severe weather over USA 26 May 2024 (left diagrams). EFI forecast of MUCAPE and MUCAPE-shear  DT 00UTC  24 May 2024, VT 00UTC 26 May to 00UTC 27 May 2024 (right diagrams).  The MUCAPE-shear EFI signal is much stronger than that of MUCAPE EFI which illustrates the importance of strong instability together with significant shear when forecasting severe convective weather.

Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

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• Further information is available on EFI forecasting for severe convection.
• Guide to Instability Indices in ECMWF output
  
• Further information is available on derivation of CAPE and Most Unstable CAPE (MUCAPE).  Describes the technique introduced in Cy47r3. 

(FUG Associated with Cy49r1)

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