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Weather warnings explanation

Met Éireann is the National Meteorological Service of Ireland and one of its most important roles is to issue weather forecasts and warnings for Ireland. This Public Weather Service mandate is primarily to protect life and ensure citizen safety. The service also supports the activities of the citizen and other agencies to mitigate damage to property and reduce disturbance to economic activity and so enhance support for impact-based decision making for weather events.

Met Éireann’s main suite of warnings are issued by the duty forecaster between 10am and midday and are updated as necessary as new information becomes available. In general, warnings will not be issued more than 48-hours ahead of the expected adverse weather but advisories on potential hazards are issued up to a week in advance.

Impacts from wind/rain/snow etc., vary depending on location, recent weather conditions, the state of ground, the time of year as well as the duration of the event. In particular the timing and location of the occurrence of extreme weather can significantly affect the impact which extreme weather may have on society, or on the economy.
The colour coding used by Met Éireann is fully aligned with international best practice and the European Meteoalarm system (www.meteoalarm.eu)

 

Yellow             Not unusual weather. Localised danger.
Orange            Infrequent. Dangerous/disruptive.
Red                  Rare. Extremely dangerous/destructive.

Local Authorities are the lead agencies for co-ordinating the response to severe weather emergencies.  Where weather emergencies are judged to impact public safety at national level the National Emergency Coordination Group (NECG) is activated by the Office of Emergency Planning on request from the Department of Housing, Planning and Local Government. This is the Lead Government Department for weather emergencies.

Met Éireann provides the weather briefings at the NECG, which brings together all Government Departments and relevant agencies and organisations, to support the locally led response and ensure coordination across the “Whole-of-Government” for the duration of the emergency.

Weather Advisories

Weather Advisories are issued up to about a week ahead to provide early information on potential hazardous weather. They may also be employed when a sum of weather elements acting together create a significant hazard, e.g. winds which may not be up to warnings strength but which, when combined with high tides and significant swell, generate a risk of flooding. Another possible use would be to advise of wind speed and direction on occasions of Volcanic Ash contamination. They might also be used to advise of expected significant medium-term accumulations of rain during a very unsettled period, when soils are known to be saturated. The issue of Weather Warnings and Weather Advisories is at all times down to the judgement of the Met Éireann Meteorologists/Forecasters.

When Will The Weather Warnings Be Issued?

In general Weather Warnings will be issued whenever weather conditions meeting the detailed thresholds defined below are anticipated within a 48-hr period. There will be judgement required on the part of the forecaster who must weigh up the possible severity of the weather conditions and the likelihood of their occurrence. However on some occasions (weekends, holiday periods) it may be necessary to issue Weather Warnings beyond this 48-hr horizon, if sufficient certainty derives from examination of the weather charts. Normally, however, a Weather Advisory (see above) will be used to flag severe weather beyond 48hrs and Advisories will normally anticipate only “Orange” or “Red” criteria weather hazards.

Given that the thrust of the Weather Warnings service is on potential “Impacts” of weather rather than on the numerical values attained by the weather elements themselves, it may on occasion be appropriate to issue warnings at a level higher than that strictly justified by the anticipated weather elements. An example would be when heavy rain was expected which might not quite meet the “Orange Warning” criteria but which might give rise to significant flooding because of already saturated ground, or because of a combination of rain, wind and tide in a coastal location.

Weather Warning Criteria

The criteria for the different warnings levels (Yellow, Orange, Red) and the different weather elements are laid out in the tables below. These numerical criteria are strong guidelines but impacts from wind/rain/snow etc., vary depending on location, recent weather conditions, the state of ground, the time of year as well as the duration of the event.

 

STATUS YELLOW

Weather that does not pose a threat to the general population but is potentially dangerous on a localised scale.

Be aware about meteorological conditions and check if you are exposed to danger by nature of your activity or your specific location. Do not take any avoidable risks

Wind
Mean speed: 10 minute
Gust: 1 minute
Widespread mean speeds between 50 and 65km/h
Widespread gusts between 90 and 110km/h
Coastal Wind Warnings
Mean speeds up to 30 nautical miles offshore
Gale force 8 / Strong Gale Force 9
Rain
Amounts can be up to double on
windward upper slopes &
impacts vary depending on for
example soil moisture deficits.
20mm – 30mm in 6 hrs or less
30mm – 40mm in 12 hrs or less
30mm – 50mm in 24 hrs
Snow/Ice 3cm or more in 24 hours
Low Temperature/Ice Air minima of minus 3C or minus 4C expected over a wide area (localised lower values will occur).
Dangerous surfaces due to ice and/or lying snow. Situation improving.
High Temperature
>27/15/>27

Maxima in excess of 27C expected and minima in excess of 15C over 36 hrs
Thunderstorm Localised thunderstorms/lightning activity/heavy rainfall
Fog (or freezing fog) Dense fog over a wide area or pockets of freezing fog

 

STATUS ORANGE

Infrequent and dangerous weather conditions which may pose a threat to life and property.

Prepare yourself in an appropriate way depending on location and activity. All people and property in the affected areas can be significantly impacted.
Check your activity/event and delay or cancel as appropriate.

Wind
Mean speed: 10 minute
Gust: 1 minute
Widespread mean speeds between 65 and 80km/h
Widespread gusts between 110 and 130km/h
Coastal Wind Warnings
Mean speeds up to 30 nautical miles offshore
Storm Force 10
Rain
Amounts can be up to double on
windward upper slopes &
impacts vary depending on for
example soil moisture deficits.
30mm – 50mm in 6 hrs or less
40mm – 60mm in 12 hrs or less
50mm – 80mm in 24 hrs
Snow/Ice 3cm or greater in 6 hrs
5cm or greater in 12 hrs
10cm or greater in 24 hrs
Low Temperature/Ice Air minima of minus 5C to minus 10C (or lower) expected over a wide area.
Dangerous surfaces due to ice and/or lying snow/freezing rain.  Situation stable.
High Temperature >30/20/>30/20/>30
Maxima in excess of 30C for three days and minima of 20C for two nights (consecutive).
Thunderstorm Widespread thunderstorms/severe lightning
activity/heavy rainfall/large damaging hail
Fog (or freezing fog) Dense fog/freezing fog persisting over a wide area
causing a widespread and significant driving hazard on
national primary routes.

 

STATUS RED

Rare and very dangerous weather conditions from intense meteorological phenomena.

Take action to protect yourself and your property.

Follow instructions and advice given by the authorities under all circumstances and be prepared for exceptional measures.

Wind
Mean speed: 10 minute
Gust: 1 minute
Widespread mean speeds in excess of 80km/h
Widespread gusts in excess of 130km/h
Coastal Wind Warnings
Mean speeds up to 30 nautical miles offshore
Violent Storm Force 11 / Hurricane force 12
Rain
Amounts can be up to double on
windward upper slopes & impacts vary depending on for
example soil moisture deficits.
Greater than 50mm in 6 hrs or less
Greater than 60mm in 12 hrs or less
Greater than 80mm in 24 hrs or less
Snow/Ice 10cm or greater in 6 hrs
15cm or greater in 12 hrs
30cm or greater in 24 hrs
Low Temperature/Ice Air minima minus 10C (or below) for three consecutive
nights or more. Maxima of minus 2C.
Dangerous surfaces due to ice and/or lying
snow/freezing rain.  Situation likely to worsen.
High Temperature As Orange criterion, but persisting for five or more
consecutive days & nights.
Thunderstorm Exceptional
Fog (or freezing fog) Exceptional

Severe Weather Chart

Storm Naming

Naming storms by National Meteorological Services has been shown to raise awareness of severe weather. It provides a clear, authoritative and consistent message to the public and prompts people to take action to prevent harm to themselves or to their property.

Met Éireann, the UK Met Office and KNMI (Netherlands) collaborate in forecasting and naming storms. The names are chosen from public suggestions and are in alphabetical order, alternating between genders.

A storm is named by a National Meteorological Service when Orange Level wind warnings are forecast to impact over a wide area overland. Orange or Red level gusts can occur in exposed areas without the event being named.

Useful Knowledge/Impact Considerations

The timing and location of the occurrence of extreme weather can significantly affect the impact which it may have on society, or on the economy

Precipitation

  • Rainfall amounts can be up to double on windward upper slopes & impacts vary hugely depending on soil moisture deficits
  • Sudden heavy downpours can lead to flash flooding and poor visibility and can be accompanied by dangerous squally winds
  • Heavy rain can turn to snow when temperatures are close to zero (up to around +4C)
  • Thunderstorms: Be aware of the dangers of lightning and do not take shelter under an umbrella or a tree. It is dangerous to be out on open water. Be careful of landline phones or any metal that connects with the ground. Lightning can strike the same spot twice

Winds

  • Winds can exceed general warning thresholds in exposed areas such as coasts and high ground and also in some low lying areas due to funneling effects
  • Trees are more vulnerable to strong winds when in leaf
  • High waves can occur on lakes as well as along coasts

Temperatures

  • Hail showers can result in potentially lethal road conditions as the hail gets quickly compacted by traffic
  • Ground temperatures can be as much as 10 degrees lower than air temperatures
  • Fog/ice can persist all day in winter months
  • Ice is not always visible on roads and surfaces
  • High night-time temperatures in Summer, can be more impactful, especially on the vulnerable, than high daytime temperatures

Seasons

In the Northern hemisphere, meteorological summer is taken as the three warmest months which are June, July and August. The three months with the most sunlight are May, June and July.

Summer: June/July/August

Autumn: September/October/November

Winter: December/January/February

Spring: March/April/May

 

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