What is a drought?
prolonged period of dry weather that dramatically lowers the water level
What are droughts caused by?
What is desertification?
- process that turns productive desert into non-productive desert as a result of poor land management
- occurs in semiarid areas bordering deserts
What causes desertification?
- cultivating of marginal lands
- destruction of vegetation in arid regions
- poor grazing management
- incorrect irrigation processes
- increasing human population and poverty
What are heatwaves?
- long periods of extreme heat that are longer and hotter than normal
- close to the ground so they affect humans, pets and vegitation
What are ice storms?
- caused by freezing rain
- rain turns into ice on contact, causing everything to be slippery and causes extra weight on power lines and roofs
What are the 3 conditions for freezing rain?
- source of moisture
- warm air over a layer of cold air
- ground temperatures at or below freezing
What are blizzards?
severe winter storms with large amounts of snow, high winds, and low visibility for extended periods of time
What causes blizzards?
interaction between upper level low pressure trough and surface low pressure
What causes Colorado & coastal storms?
moist ocean air
What causes Alberta Clippers?
dry air with less snow and cold temperatures
What causes Nor'easters?
hurricane winds, heavy snows, intense precipitation, high waves
What are the atmospheric conditions for a thunderstorm?
- warm, humid air in the lower atmosphere
- cold air above warm air
- updraft must force air into the upper atmosphere
What are the different stages in a thunderstorm?
- cumulus stage
- mature stage
- dissipative stage
What is required to be a severe thunderstorm?
- winds greater than 58 mph
- hailstones bigger than .75"
- or generates a tornado
What are the necessary conditions for a severe thunderstorm?
- greater wind sheer, greater storm
- high water vapor content in lower atmosphere
- updraft of air
- dry air mass above a moist air mass
What are the types of severe thunderstorms?
- MCSs (mesoscale convective systems) most common
- squall lines
What are MCSs?
large clusters of self-propagating storms
What are squall lines?
- long lines of individual storm cells
- anvil shaped clouds form
- can develop along drought lines
What are supercells?
- smaller than other two but more damaging
- spawn the most tornadoes
- 12-30 miles in diameter
- last between 2 and 4 hours
What are tornadoes?
vortex extending downward from the cloud and touching the ground
Where do tornadoes form?
form where there are large differences in atmospheric pressure over short distances
What are the three stages of a tornado?
- organizational stage
- mature stage
- shrinking stage
- rope stage
What occurs in the organizational stage?
- updrafts tilt horizontally, rotating the air vertically
- cloud begins to lower and funnel descends
What occurs in the mature stage?
- funnel extends to ground
- moist air is drawn up
- suction and damage occur
What occurs in the shrinking stage?
- warm air is reduced
- tornado begins to thin
What occurs in the rope stage?
funnel moves erratically and then disappears
What is the Fujita scale?
- measures internal windspeeds and damage produced
- measured F0 to F5
- updated in 2007
- now based on detailed wind measurements and long-term damage records