The Description Below Was Taken From The Metoffice:

Regional flash warnings of severe weather and UK advance warnings of severe weather are issued when the following conditions are expected:

• Severe gales
• Heavy snow
• Heavy rain
• Dense fog
• Freezing rain/widespread icy roads

These warnings are classified as exceptionally severe when the following conditions are expected:

• Severe gales/storms
  
• Very heavy snowfall, blizzards or drifting snow

Term used Meaning Severe Gales: Gusts of 70 m.p.h. or more. Severe Gales/storms: Gusts of 80 m.p.h. or more. Heavy Snow: Snow falling at a rate of approx. 2 cm/hour or more expected for at least two hours. Blizzards/drifting snow: Moderate or heavy snow accompanied by winds of 30 m.p.h. or more with visibility reduced to 200 m or less, or drifting snow giving rise to similar conditions.   Very heavy snowfall, blizzards or drifting snow:   Expected to give depths of 15 cm or more potentially resulting in widespread dislocation of communications. Blizzards are severe when visibility is reduced to near zero.   Heavy rain:     Expected to persist for at least two hours and to give at least 15 mm within a three-hour period, or a period of rainfall of sufficient intensity to cause flooding on already saturated ground (includes snow-melt), i.e. around 25 mm/day.   Dense Fog:   Visibility generally less than 50 m. Freezing rain/widespread icy roads: Generally occurs when rain freezes on contact with road surfaces.