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Fig9.6.1-18(b): Bulk Wind Shear (Orange high, Yellow low).  T+24 VT00UTC 11 July 2019, DT00UTC 10 July 2019.  

Fig9.6.1-1819(a): Forecast CAPE-SHEAR (Purple high, Blue low).

Fig9.6.1-1819(b): Max CAPE-SHEAR (Red high, Blue low).  T+24 VT00UTC 11 July 2019, DT00UTC 10 July 2019.  Very high values are indicated in the vicinity of Pilio.  More modest values are indicated in the vicinity of Kavala on the CAPE-SHEAR chart but note that the maximum CAPE-SHEAR chart shows there have been much higher values during the previous 6hrs.

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The forecast precipitation field (Fig9.6.1-19) shows a belt of rainfall across North Greece, Albania and Bulgaria.  This indicates that, as a minimum, in this area there is sufficient moisture in the forecast atmosphere to provide precipitation.  The area of forecast precipitation intersects the northern flank of the forecast CAPE and CAPE-SHEAR areas and thus it is this area that is more likely to see release of deep and active convection with availability of plenty of moisture.   Little or no precipitation is indicated in mid-Greece but nevertheless these lie within the areas of very high CAPE and isolated but local very heavy showers are possible and, bearing in mind the high bulk shear and CAPE-SHEAR values, local storms cannot be ruled out. 

Fig9.6.1-1920: Forecast precipitation (12hr). T+24 VT00UTC 11 July 2019, DT00UTC 10 July 2019.

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The corresponding diagnostic charts for the probability of high rainfall (>40mm/24hr) and Extreme Forecast Index (EFI) for precipitation (Fig9.6.1-20(a) & Fig9.6.1-20(b)) identify the areas at greatest risk of a major precipitation event.     

Fig9.6.1-2021(a): Probability of total precipitation >40mm (24hr).  Green shading represents 35-65% probability.

Fig9.6.1-2021(b): Precipitation extreme forecast index (EFI).  Red shading represents EFI>0.8, Dark red >0.9 EFI. T+24 VT00UTC 11 July 2019, DT00UTC 10 July 2019.

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Violent storms with local hail swept across northern Greece overnight 10/11 July 2019 causing seven deaths and widespread damage.

Fig9.6.1-2122: Forecast vertical profiles for Kavala and Pilio, Greece. T+24 VT00UTC 11 July 2019, DT00UTC 10 July 2019.

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A sequence of forecast EFI charts gives early indication of forthcoming severe weather potential (Fig9.6.1-22), and some idea of the confidence that may be placed on the forecast event.  In this case, northern Greece is identified as being at moderately high risk of an extreme event (EFI ~ 0.6) four days before, rising steadily to a very high risk of an extreme event (EFI ~ 0.9) two days before the occurrence of the severe weather.  Note how there is consistent indication of a very high risk of an extreme event (EFI ~ 0.9) over the Balkan states through the sequence of forecast runs.  The consistency in the areas shown at risk leads to a higher confidence in forecasts of severe weather.  Users should inspect forecast fields using ecCharts and vertical profiles as outlined above to assess forecast details, and also add in the influence of additional factors using local knowledge (e.g. regarding topographic influences) wherever possible.   

Fig9.6.1-2223: Sequence of EFI precipitation charts from four EFI runs at 24hr intervals (DT 12UTC on 6, 7, 8, 9 July 2019). Increasingly high EFI precipitation values identify the areas at greatest risk.

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CONTROL-10/HRES tends to over-forecast extreme convection, especially in the maritime tropics.  Spurious quasi-circular waves (sometimes rings) in convective precipitation fields can emanate from the forecast rapid uplift that is associated. These spread outwards. The gravity waves can even move well upwind, giving a false impression of an eastward-moving trough.  The source of these false features should be recognised and their effects discarded from forecasts. Changes to the IFS moist physics in 2019 have mitigated but not entirely removed this effect. 

Fig 9.6.1-2324: An example of a forecast precipitation chart showing a very active convective area in the mid-Indian Ocean. The surrounding ring of forecast precipitation is associated with a spurious gravity wave (ripple effect) moving outward from the initial convective cell.  These rings of precipitation are incorrect and should be ignored.

Fig9.6.1-2425: Ensemble control/HRES forecast of precipitation associated with gravity waves propagating outward across central Africa from a pulse of very strong convection formed over the Gulf of Guinea (just to the southwest of the charts).  Model precipitation rate are shown for one such feature at T+120, T+132, T+144, data time 00Z 3 Sept 2018. The apparent trough is propagating anomalously against the flow and the precipitation is not correct. 

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