Whirlwinds

Whirlwinds is a general term, covering all rotating wind storms which originate on the ground with a column of air spiraling upwards. Less vigorous vortices are called dust devils or if over the sea or lake water devils.

Tornadoes

Tornadoes are the most violent of wind systems. Spinning centres of over 180 km/hr (120 mph) - and sometimes much higher can occur, while the body of the storm moves over the land at 40-65 km/h (25-40 mph).

Each tornadoe is only a few hundred metres in diameter, yet contains as much energy as one night's street lighting in New York City.

As the funnel of the storm touches ground much damage can occur with large objects sucked into the storm which extensive damage to buildings. Across our globe tornadoes are very common affairs, the most frequent and severe across the Great Plains of the US, along a track through nine states called "Tornadoe Alley".

Air strongly heated from below, rushes upward to form an active convection cell, within this convection cell air rises at up to 165km/h (100 mph) inside the storm cloud. Winds at the top of the storm cloud starts to rotate at very high speed.

More air flows inward and the rotation extends downwards, narrowing as it does so. It's spin becomes faster. Very low pressure in the vortex causes water vapour to condense, making the funnel easily visible.

Because it is the same shape as a brass instrument, the top of the tornadoe is called a "tuba".

When a tornadoe passes over a building, the difference in pressure can make a building explode.

Water Spouts and Dust Devils

Water spouts are vortices of air over a water source. They usually form over land then on to water when they rapidly callapse.

Dust Devils occur during warm or hot summer spells, many was logged in the summer of 1975/76. Surfaces heats up into the day from strong hot sunlight. When the pressure wind flow is more than 10 mph or (16 km/h), the heated air rising into the horizontal air flow starts to spin. Usually the vortex sucks up dust, paper and other items into it's spinning centre, so it's visible, but on occasions there are no sign of dust and is invisible, and are only detectable by a sudden burst of wind accompanied by a hissing noise, knocking over dustbins and patio sets.

Next Week.....Hurricanes

The answer to last week's question was 4 miles.This week's question is:What is the name of the Alley in United States where tornadoes are frequent and most severe:A/ Dust Bowl Alley.B/ Tornadoe Alley.Glossary of Common Weather TermsCloudy: A cloudy day is one where the total cloud covers or nearly covers the entire sky.Cloud type of the week:

Cumulus (Cu): Detached heaped clouds, in the form of rising domes or towers. Brilliant white cauliflower shapes, with dark bases towards the horizon. Height of base 1,500 ft to 6,500 ft. Fair weather cumulus and shower cumulus are the two main types.

Weather for week Monday 23rd April-Friday 28th April Varied weather conditions through this period with fair warm spells alternating with short lived showery intervals, no sign of any real substantial rain through this period.

Frost free conditions overnight.

Maximum day temperature between 17 and 22c 63-72f.Minimum night temperature between 5 and 8c 41-46f.Last Week's Observations for Worcester (Monday-Friday)Highest day temperature............20.6c 70f on Thursday 19th April.Lowest night temperature..........2.2c 36f on Wednesday 18th April.Wettest day..............................No rainfall logged.