The list and the criteria of the dangerous and hazardous hydrometeorological phenomena and of the sudden weather changes

Dangerous phenomena:
Thunderstorms.
Storms and winds in gusts of 15 m/s and more.
Fog of 200 m and less visibility that lasts 3 hours and more.
Heavy rains with a precipitations amount of 15-49 mm accumulated in 12 hours.
Hail with diameter of 6-19 mm.
Heavy snowfalls with a precipitations amount of 7-19 mm accumulated in 12 hours.
Snowstorm with wind speed of more than 11 m/s, more than 3 hours.
Sleet deposits with diameter of 11-34 mm.
Glazed frost with diameter of 6-19 mm.
Icy roads.
Heat waves – air temperature of +33°C and more.

Hazardous phenomena:
Storms and winds in gusts of 25 m/s and more.
Heavy rains with a precipitations amount of 50 mm and more, accumulated in 12 hours, or with a precipitations amount of 30 mm and more, accumulated in 1 hour.
Long lasting rains with a precipitations amount of 120 mm and more, accumulated in 1-3 days.
Big hail with diameter of 20 mm and more.
Heavy snowfalls with a precipitations amount of 20 mm and more accumulated in 12 hours.
Snowstorm accompanied by snow drifting.
Fog of 50 m and less visibility that lasts more than 24 hours.
Glazed frost with diameter of 20 mm and more.
Ground frosts – negative air temperatures at a 2 m height and at the soil surface during the vegetation period.
Severe frost – air temperature of -25°C and less.
Exceptional fire risk.

Sudden weather changes:
Decrease of the maximum or minimum air temperature by 10°C and more during the cold period of the year.
Decrease of the air temperature by 10°C and more in 6-12 hours.
Replacement of the period without precipitations (3-5 days and more) with a period with precipitations (3-5 days and more) and vice versa.