Reflect

Alert and Activation Criteria

SkyWarn UK operates a combined weather alert and spotter activation system. Details of our alert and activation criteria are below:

All Clear (GREEN) - No active Convective Weather Advisory, Convective Weather Warning, or Severe Weather Warning. The spotter network is not activated.

Convective Weather Advisory (AMBER) - A Convective Weather Advisory is issued when there is a significant risk of any of the following (in direct association with a convective weather event such as thunderstorms or squalls):
• Marginally severe hail (15 to 20 mm diameter)
• Isolated / weak tornadoes (T0 - T1)
• Marginally severe winds (55 to 60 mph)

Convective Weather Warning (RED) - A Convective Weather Warning is issued when there is a significant risk of any of the following (in direct association with a convective weather event such as thunderstorms or squalls):
• Severe hail (over 20 mm diameter)
• Severe wind gusts (over 60 mph)
• Flooding rains
• Multiple / strong tornadoes (T2 intensity or higher)
• Possible LT supercells

Severe Weather Warning (RED) - A Severe Weather Warning is issued when there is a significant risk of any of the following (NOT in direct association with a convective weather event such as thunderstorms or squalls):
• Heavy rain likely to lead to localised flooding (generally in excess of 25 mm / 24 hrs)
• Heavy / disruptive snowfall (generally in excess of 5 cm)
• Damaging winds (gusts in excess of 70 mph)
• Storm (heavy rainfall in excess of 25 mm / 24 hrs AND wind gusts in excess of 70 mph)
• Winter Storm (heavy snowfall of at least 5 cm AND wind gusts in excess of 40 mph)

Spotters will be asked to report any event meeting the advisory / warning criteria as above.

posted in Alert & Activation Criteria01.12.09