Status:Ongoing analysis Material from: Linus, Fernando, ...


1. Impact

The windstorm Poly caused severe disruption on 5 July in the northern part of Netherlands, due to extreme windgusts, especially for being from a summer cyclone. The media mentioned that schools were closed in some regions, air traffic paused and the trains were also affected because of fallen trees in the tracks and overhead wires. 2 dead person is reported (–23_European_windstorm_season#Storm_Poly) and several injuries due to flying debris. The red warning for Netherlands was issued yesterday evening or today after a yellow warning issued yesterday.

2. Description of the event

The plots below show analyses of MSLP and 6 hour rainfall from 3 July 00UTC to 6 July 00UTC, every 12th hour. The development started on 4 July with heavy rainfall on southern England and the cyclone quickly intensified over the north Sea.

The plots below show analyses of z500 and T850 from 2 July to 7 July 00UTC, every 24 hour.

The satellite images below show the evolution of the cyclone in the morning of 5 July. There are some evidence of a sting jet in the satellite signature.

3. Predictability

3.1 Data assimilation


3.2 HRES

The plots below show 24-hourmaximum wind gusts (5 July 00UTC - 6 July 00UTC) in observations (first plot) concatenated short forecasts (second plot) and HRES forecasts with different lead times. 

3.3 ENS

The plots below shows EFI and SOT for 1-day  wind gusts on 5 July, from different initial dates. While there was a signal in the SOT early on, the strong signal in EFI appeared on 4 July.

The plot below shows the forecast evolution plot for 24-hour maximum wind gusts (5 July 00UTC - 6 July 00UTC) at Schiphol Airport near Amsterdam. Mean of observations - green, HRES –red, ENS blue box-and-whisker, Model climate – red box-and-whisker. Ensemble mean as black diamonds. Triangle marks the maximum in the model climate based on 1200 forecasts. While some members had extreme wind gusts in forecasts from 30 June-1 July, the ensemble picked up the extreme signal over the last 2 days before the event.

The plots below shows cyclone features coloured by maximum wind speed within 300 km on 5 July 12UTC.

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

  • Some medium-range signal i a few members (for the right synoptic reason?)
  • Late (1.5-2 day) capturing of the cyclone

6. Additional material