Download Severe Weather Notes

Objective 1. Students will explain how each of the following
types of severe weather is formed.
III. Severe Weather
A. Graupel: is small, light weight, frozen H2O that forms balls
or spheres that do not create ice or crystals (hence not hail
or snow). It is created when rain falls into cooler temps,
freezes, gets blown back up by wind (updraft), falls again
and collects tiny droplets of H2O that freeze to it on the
way down.
B. Hail: is formed when rain falls through colder temps,
freezes completely (ice), catches an updraft, and collects
water that freezes completely to it. It will continue the
updraft, drop, freeze cycle until it is too heavy to remain in
the air.
C. Snow forms when water falls in colder temps, freezes into
a crystalline (crystal lattice) and continues to the ground.
D. Sleet forms when a rain drop freezes, melts slightly (due to
warm air) before hitting the ground. Sleet appears at an
angle because it is usually accompanied by strong winds.
E. Rain forms as a result of condensation or coalescence
(collisions of water vapor) that is too heavy for the cloud.
F. Thunderstorms form when cumulonimbus (nimbus means
storm) clouds, high winds, hail, rain, thunder and lightning
all combine. The thunder heads produce massive
condensation which creates friction; this quick build up of
clouds produces static charges. The static charges get
discharged as lightning when the + or – from the clouds
meets the + or – from the ground.
G. Tornadoes occur when warm moist air goes up, cool dry
air goes across which creates wind shear that causes the
air to rotate and tilt becoming the funnel cloud. The
funnel cloud touches ground (tornado) or water (water
spout).
H. Hurricanes are storms that occur over oceans or seas
when warm, moist air rises into pre-existing winds which
create a low pressure area. This causes high pressure to
move in to fill the low pressure, creating clouds containing
winds that move in a circular motion. Other names for
hurricanes: in the Western Pacific Ocean and China seaTyphoons, in the Indian ocean-Cyclones, in Northwest
Australia’s Timor sea-Willy Willies.