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 Status: Finalised Material from: Linus, Ivan


 


1. Impact

The news reports of devastating flash floods in Greece 15 November, just west of Athens (e.g http://www.bbc.co.uk/news/world-europe-41998374). At least 15 people were killed. The news reports say that heavy rainfall fell overnight, which I interpret as before 06UTC. It is therefore a bit surprising that the maximum observation covering 14 Nov 06UTC - 15 Nov 06UTC in the region around Athens is 11 mm (Elefis Airport, close to Mandras where the flooding took place).

2. Description of the event

The plot below shows the 24-hour accumulated precipitation between 14 Nov 06UTC - 15 Nov 06UTC. Note the low values around Athens, while the west coast had widespread high precipitation.


On the satellite RGB airmass animation we can detect convection across the broad Athens area which organizes into a linear mesoscale convective system (MSC). Looking at the shape of this MSC we probably could classify it as a trailing stratiform type of MSC. This type of MSCs being parallel to the main flow tends to produce prolonged periods of intense rainfall. We still do not have any good estimates how much rain that fell in the mountains north-west of Athens, that caused the flash-floods.


3. Predictability

  

3.1 Data assimilation

 

3.2 HRES

The plot below shows the last HRES before the event. The amounts Athens was 20-30 mm/24h.



3.3 ENS

The plots below show the 95th percentile of the 12-hour precipitation from the raw ensemble (left) and the point-rainfall product (right). Looking at the 95th percentile from the ensemble no extreme is visible in the area, and the point rainfall product does not increase the 95th percentile significantly

The plot below shows the convective hazard forecast based on ENS, T+24-48h valid for 15 November. Here the region around Athens was highlighted as a potential area for severe convection.



3.4 Monthly forecasts


3.5 Comparison with other centres


4. Experience from general performance/other cases


5. Good and bad aspects of the forecasts for the event

  • Difficult event to evaluate due to lack of observations
  • No signal in HRES or ENS precipitation
  • Convective hazard map gave some guidance

6. Additional material

 Status:Ongoing analysis Material from: Linus, Ivan


 


1. Impact

The news reports of devastating flash floods in Greece 15 November, just west of Athens (e.g http://www.bbc.co.uk/news/world-europe-41998374). At least 15 people were killed. The news reports say that heavy rainfall fell overnight, which I interpret as before 06UTC. It is therefore a bit surprising that the maximum observation covering 14 Nov 06UTC - 15 Nov 06UTC in the region around Athens is 11 mm (Elefis Airport, close to Mandras where the flooding took place).

2. Description of the event

The plot below shows the 24-hour accumulated precipitation between 14 Nov 06UTC - 15 Nov 06UTC. Note the low values around Athens, while the west coast had widespread high precipitation.


On the satellite RGB airmass animation we can detect convection across the broad Athens area which organizes into a linear mesoscale convective system (MSC). Looking at the shape of this MSC we probably could classify it as a trailing stratiform type of MSC. This type of MSCs being parallel to the main flow tends to produce prolonged periods of intense rainfall. We still do not have any good estimates how much rain that fell in the mountains north-west of Athens, that caused the flash-floods.


3. Predictability

  

3.1 Data assimilation

 

3.2 HRES

The plot below shows the last HRES before the event. The amounts Athens was 20-30 mm/24h.



3.3 ENS

The plots below show the 95th percentile of the 12-hour precipitation from the raw ensemble (left) and the point-rainfall product (right). Looking at the 95th percentile from the ensemble no extreme is visible in the area, and the point rainfall product does not increase the 95th percentile significantly

The plot below shows the convective hazard forecast based on ENS, T+24-48h valid for 15 November. Here the region around Athens was highlighted as a potential area for severe convection.



3.4 Monthly forecasts


3.5 Comparison with other centres


4. Experience from general performance/other cases


5. Good and bad aspects of the forecasts for the event

  • Difficult event to evaluate due to lack of observations
  • No signal in HRES or ENS precipitation
  • Convective hazard map gave some guidance

6. Additional material