A meteorological threshold, for example 50 millimetres of rain in 24 hours, is not necessarily needed to be met in order for a warning to be issued. If the anticipated rainfall is expected to have an impact, an alert will be issued. Picture for illustration: iStock
The South African Weather Service (SAWS), in collaboration with the department of disaster management, recently announced that a new weather warning service has been introduced across South Africa.
The new service, known as the impact-based severe weather warning system, will change the current threshold-based alerts to impact-based ones, reports Lowvelder.
What this means is that a meteorological threshold, for example 50 millimetres of rain in 24 hours, is not necessarily needed to be met in order for a warning to be issued.
If the anticipated rainfall is expected to have an impact, an alert will be issued.
The new colour-coded impact-based weather forecast service. Picture: SAWS website
What you can expect from the new system:
• Warnings will be easier to understand;
• Less use of meteorological jargon and scientific wording;
• They only issued if an impact is expected to occur;
• They will be easier to translate;
• They will be unique to hazard and area; and
• Joint ownership of warnings between the SAWS and disaster management.
Impact-based warnings will be issued for the following hazards:
• Disruptive rainfall,
• Severe thunderstorms (heavy downpours/large hail/large amounts of small hail/damaging winds),
• Damaging winds,
• Disruptive snowfalls,
• Reduced visibility,
• Damaging waves, and
• Storm surges.
Warning levels will be colour-coded, using the traffic light system (yellow, orange and red). The colours will be dependent on the combination of the anticipated impacts and the likelihood of it occurring.
Fire danger alerts will, however, still be issued according to thresholds as these are governed by an Act of parliament. A warning will be issued if the index is higher than 75. A full fire danger index forecast map is available at www.weathersa.co.za/home/fireindexand and is updated daily.
In addition to weather warnings, advisories will be issued for the following phenomena:
• Extremely high temperatures: When the maximum temperature is expected to be at least 40°C.
• Extremely low temperatures: When the maximum temperature is expected to be 10°C or below.
• Heatwave conditions: The maximum temperature is 5°C higher than the average temperature for the hottest month for three consecutive days.
• High discomfort is considered when the temperatures exceeds 42°C and the relative humidity is at least 40%.
• Frost: The first frost of the season or where frost is not a common occurrence in the area. The purpose of issuing an advisory is just to alert the general public to the possibility of unusual conditions relating to temperature. These are not necessarily life-threatening if prepared for accordingly.
The main aim of the impact-based severe weather warning system is for related warnings to be better understood so that they reach more South Africans, and the required action can be taken well ahead of time in order to mitigate possible impacts.
This article was republished with permission from Caxton publication Lowvelder. Read the original article here.
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