SCIENCE NEWS

Severe Weather

characteristics of a Severe Thunderstorm Fueled by the increased instability of the air Intense rotating updrafts as strong as 240km/h and lasting several hours Know to produce: large hail, strong surface winds, heavy rain and tornadoes

Severe thunderstorms National Weather Service: - 3/4 inch hail and/or 50 knot wind gusts at the surface required to use term “severe” The big difference from ordinary t-storms is that many severe storms have a tilted updraft this keeps the downdraft from eventually killing the storm

SUPERCELLS Severe thunderstorms What is the name of a severe thunderstorm that developed into a self sustaining extreme storm? SUPERCELLS

SUPERCELLS

Remember ???? A cell is formed in the Mature Stage of a thunderstorm from the up/downdraft An anvil shape of the cumulonimbus cloud appears as the updrafts hit the tropopause

SUPERCELLS

SUPERCELLS

SUPERCELLS & Strong Winds Winds speeds over 160k/hm Violent concentration of downdrafts in a local area known as downbursts

DOWNBURSTS Classified by size of affected area Macroburst: destruction up to 5 km wide, wind exceeds 200 km/h, last up to 30 min. Microburst: destruction up to 3 km wide, winds exceed 250 km/h, less than 10 min

Macrobursts

Microbursts

SUPERCELLS & Hail Hail Collision of super cool water drops forms layers Formation from an abundance of strong up & down drafts

SUPERCELLS & Tornadoes a violent whirling column of air in contact with the ground

Super cell that produced a tornado

TORNADOES Occurrence Annually, the US has more than 1000 tornadoes but the highest frequency is observed in tornado alley of the Central Plains. Nearly 75% of tornadoes form from March to July, and are more likely when warm humid air is overlain by cooler dryer air to cause strong vertical lift.

TORNADOES Features Violent windstorm Rotating column of air that extends down from a cumulonimbus cloud Low pressures inside causes the air to rush into Smaller suction vortices can form inside stronger tornadoes

Rotating clouds are the first sign that a super cell may form a tornado

TORNADOES Diameter between 500 & 2000 ft Characteristics Diameter between 500 & 2000 ft Speed across landscape about 30 mph Cut about a 6 miles long path Most move toward the northeast Intensity measured by the Fujita intensity scale

Tornado Wind Speed As the tornado moves along a path, the circular tornado winds blowing opposite the path of movement will have less speed. Example if the storm rotational speed is 100 knots, and its path is 50 knots, it will have a maximum wind of 150 knots on its forward rotation side.

Tornados

Fujita Intensity Scale

Fujita-Damage Scale

Tornado damage

F5 Tornado damage

Tornado Damage

Other TORNADOES Funnel Clouds Rotating columns of air Wind speed may exceed 200 knots When the funnel cloud reaches the ground it becomes a tornado When the funnel cloud reaches the water it becomes a waterspout

Waterspout

Dust-devil

ANY QUESTIONS?

HOMEWORK Read p 350 – 354