Alert levels

Heat Alert Forecasting and Supporting Information

The service uses information from the national “Hot weather planning advice forecast” service that is issued to public authorities and health professionals in Sussex by the Met Office.

The forecasts are supported by information provided by Public Health England’s Heatwave Plan for England. The plan describes the heat-health watch system which operates in England from June to September each year. During this period, the Met Office may forecast heatwaves, as defined by forecasts of day (31°C) and night-time (16°C) temperatures and their duration, as set out below.

View the Heatwave Plan for England

What the Heatwave Plan Levels mean (Heatwave Plan for England 2014 (updated May 2022)

Level 1 Heatwave and Summer preparedness programme June to September
Level 2 Heatwave is forecast – Alert and readiness 60% risk of heatwave in the next 2 to 3 days
Level 3 Heatwave Action – temperature (daytime 31°C or night time 16°C) reached in one or more Met Office National Severe Weather Warning Service regions
Level 4 Emergency response – Central government will declare a Level 4 alert in the event of severe or prolonged heatwave affecting sectors other than health

* Older adults and children with heart or lung problems are at greater risk of symptoms developed as a result of severe hot weather.

Level 1: Heatwave and Summer Preparedness

Summer preparedness runs from June to September when a Level 1 alert will be issued.

The heatwave plan will remain at Level 1 unless a higher alert is triggered. During the summer months, social and healthcare services need to ensure that awareness and background preparedness are maintained by implementing the measures set out in the heatwave plan.

Level 2: Alert and Readiness

This is triggered as soon as the Met Office forecasts that there is a 60 per cent chance of temperatures being high enough on at least two consecutive days to have significant effects on health. This will normally occur 2 to 3 days before the event is expected.

As death rates rise soon after temperature increases, with many deaths occurring in the first two days, this is an important stage to ensure readiness and swift action to reduce harm from a potential heatwave.

Level 3: Heatwave Action

This is triggered as soon as the Met Office confirms that threshold temperatures have been reached in any one region or more. This stage requires specific actions targeted at high-risk groups.

Level 4: Major Incident

This is reached when a heatwave is so severe and/or prolonged that its effects extend outside health and social care, such as power or water shortages, and/or where the integrity of health and social care systems is threatened. At this level, illness and death may occur among the fit and healthy, and not just in high-risk groups and will require a multi-sector response at national and regional levels.

The decision to go to a Level 4 is made at national level and will be taken in light of a cross government assessment of the weather conditions, co-ordinated by the Civil Contingencies Secretariat (Cabinet Office).

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