Impact Based Forecasting - Hanoi © Crown copyright Met Office

Recap... Introduction to weather and forecasting Hazard and impact matrices Impact based weather forecasting Impact tables

Impact tables in the UK © Crown copyright Met Office

Impact and likelihood Not just the nature of severe weather up to 5 days ahead – no weather thresholds Impact based system Two factors Likelihood of impacts occurring Confidence in forecast The level of impacts expected – dependent on: Location Timing Recent weather © Crown copyright Met Office

Considerations relating to Impact General Is the bad weather expected during a rush hour? Are there reasons for there being more travellers/outdoor activities in the area of the warning? Greater risk of Road Traffic Accidents? In the area of concern are there any local “hot-spots” i.e. areas prone to the particular weather hazard (such as wind and flooding) Are there any significant outdoor events at which large numbers of people could be adversely affected? Are there “politically” sensitive areas, such as areas which have flooded badly recently? © Crown copyright Met Office

Considerations relating to Impact Rain Does the rain follow a prolonged dry spell? Is the rain a continuation of a prolonged wet spell? Is the ground already saturated? Is the heaviest rain falling over urban areas? Is it falling during a rush hour or a major public event? © Crown copyright Met Office

Considerations relating to Impact Wind Are the trees in full leaf? Is the ground saturated? Is the wind from an unusual quadrant? Is the wind unseasonal? Is the wind affecting a major public outdoor event Have there been previous strong wind events possibly weakening structures? Will there be a significant cross wind component on key roads, especially bridges? © Crown copyright Met Office

The Matrix Colour determined by the combination of the likelihood and the impacts

Storm Timeline - 28th October 2013

Wednesday 23rd October The Guidance – Moderate risk that some sort of “low prob, high impact” warning for wind will be issued tomorrow for Monday – still significant uncertainty in track and depth of low, but could be a very significant feature/event Still outside the five day warning time period so nothing can be issued. © Crown copyright Met Office

Thursday 24th October Increasing likelihood that a major storm will move across the UK. Still much uncertainty over the track of the storm but… Time to issue alerts © Crown copyright Met Office

Despite uncertainty over track of storm still enough confidence to highlight an AMBER area Very low likelihood of High impacts Low likelihood of High impacts

Still uncertainties so impact and likelihood assessments similar but areas now larger Very low likelihood of High impacts Low likelihood of High impacts

Saturday 26th October Differing details still giving a spread to the possible tracks Increasing confidence in levels of damaging winds so increased likelihood of high impacts © Crown copyright Met Office

Increasing likelihood of high impacts in the AMBER area Very low likelihood of High impacts Medium likelihood of High impacts

Sunday 27th October – the day before Much narrower spread to possible tracks Still a medium likelihood of high impacts, particularly to the south of the storm’s track Lesser impacts expected to the north of the track so Yellow warning modified accordingly

Sunday 27th October Low likelihood of Medium impacts Medium likelihood of High impacts

And finally, it blows through quicker than expected so… Warning is cancelled

The damage © Crown copyright Met Office

Any questions? © Crown copyright Met Office