Weather Warnings are presented in three categories:
A. STATUS YELLOW – Weather Alert – Be Aware
The concept behind YELLOW level weather alerts is to notify those who are at risk because of their location and/or activity, and to allow them to take preventative action. It is implicit that YELLOW level weather alerts are for weather conditions that do not pose an immediate threat to the general population, but only to those exposed to risk by nature of their location and/or activity.
B. STATUS ORANGE – Weather Warning – Be Prepared
This category of ORANGE level weather warnings is for weather conditions which have the capacity to impact significantly on people in the affected areas. The issue of an Orange level weather warning implies that all recipients in the affected areas should prepare themselves in an appropriate way for the anticipated conditions.
C. STATUS RED – Severe Weather Warning – Take Action
The issue of RED level severe weather warnings should be a comparatively rare event and implies that recipients take action to protect themselves and/or their properties; this could be by moving their families out of the danger zone temporarily; by staying indoors; or by other specific actions aimed at mitigating the effects of the weather conditions.
What weather conditions are warned for?
Hazards deriving from the following weather-related types are covered by Kitasweather:
4. Low Temperatures
6. High Temperatures
8. Coastal Wind Warnings
When will Weather Alerts/Warnings be issued?
Weather Alerts and Warnings will be issued whenever weather conditions meeting the detailed thresholds defined below are anticipated within a 48-hr period. There will be judgment required on 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 below) 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 Advisories may be issued to provide early information on potential hazardous weather beyond the 48hr horizon. 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. 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 judgment of Kitasweather.
Weather Warning Criteria
The criteria for the different warnings levels (Yellow, Orange, Red) and the different weather elements (Rain, Wind etc) are laid out in the tables below.
Categories of Severe Weather encompassed by the National Weather Warnings System, together with the associated criteria:
Weather Element Criteria for Red – Severe Weather Warnings
1. Wind Mean Speeds in excess of 80 km/h
Gusts Speeds in excess of 130 km/h
2. Rain 70mm or greater in 24 hrs
50mm or greater in 12 hrs
40mm or greater in 6 hrs
3. Snow/Ice Significant falls of snow likely to cause accumulations of 8 cm or greater below 250 m AMSL. Slippery paths and roads due to accumulation of ice on untreated surfaces; situation likely to worsen.
4. Low Temperatures Minima of minus 10C or lower expected. Maxima of minus 2C or lower expected.
5. Fog No Criterion – not displayed.
6. High Temperature Maxima in excess of 44C for the Central Plain, 41 for coastal areas and 39 for the mountains above 1100m. or minima in excess of 28C expected for two or more consecutive nights.
7. Thunderstorms No Criterion – not displayed.
8. Coastal Wind Warnings Violent Storm Force 11 or greater. (Mean Speeds)
Weather Element Criteria for Orange – Weather Warnings
1. Wind Mean Speeds between 65 and 80 km/h
Gusts between 110 and 130 km/h
2. Rain 50mm – 70mm in 24 hrs
40mm – 50mm in 12 hrs
30mm – 40mm in 6 hrs
3. Snow/Ice Significant falls of snow likely to cause accumulations of 3 cm or greater below 250m AMSL. Slippery paths and roads due to accumulation of ice on untreated surfaces; situation stable.
4. Low Temperatures Minima of minus 5C to minus 9C expected. Maxima of 0C or minus 1C expected.
5. Fog Dense fog likely to cause a widespread and significant driving hazard on national primary routes.
6. High Temperature Maxima in excess of 42C for the Central Plain, 39 for coastal areas and 36 for the mountains above 1100m. or minima in excess of 26C expected in a 24hr period.
7. Thunderstorms Widespread thundery activity over a large area of the Island.
8. Coastal Wind Warnings Storm Force 10. (Mean Speeds).
Weather Element Criteria for Yellow – Weather Alerts
1. Wind Mean Speeds between 50 and 65 km/h
Gusts between 90 and 110 km/h
2. Rain 30mm – 50mm in 24 hrs
25mm – 40mm in 12 hrs
20mm – 30mm in 6 hrs
3. Snow/Ice Scattered snow showers giving accumulations of less than 3 cm below 250m AMSL. Slippery paths and roads due to accumulation of ice on untreated surfaces; situation improving.
4. Low Temperatures Minima of minus 3C or minus 4C expected. Maxima of plus 1C or plus 2C expected.
5. Fog No Criterion.
6. High Temperature Maxima in excess of 40C expected for the Central Plain, 37 for coastal areas and 33 for the mountains above 1100m altitude.
7. Thunderstorms No Criterion.
8. Coastal Wind Warnings Gale Force 8 or Strong Gale Force 9. (Mean Speeds)
Weather Element Criteria for Green (i.e. no significant hazardous weather)
1. Wind Gusts less than 80 km/h
2. Rain Less than 30mm in 24 hrs
Less than 25mm in 12 hrs
Less than 20mm in 6 hrs
3. Snow/Ice No snow, or some snow showers possible, mainly above 250m altitude.
4. Low Temperature Minima higher than minus 3C and maxima higher than plus 2C.
5. Fog None
6. Thunderstorms None
7. High Temperature Maxima less than 27C
8. Coastal Wind Warnings Winds less than Gale Force.