Storms and Weather Forecasts

Chapter 30

Thunderstorm

• Small area storms formed by a strong upward movement of warm, unstable moist air.

Air-mass thunderstorm

• Form within a warm, moist air mass.

• Often single storms.• Occur mostly in

spring and summer.• Usually last less than

an hour.

Frontal thunderstorm

• Usually form in warm, moist air on or ahead of a cold front. Some do occur in front of warm fronts.

Squall Lines

• Line of heavy precipitation and t-storms in front of a cold front.

Lightning

• A discharge of electricity from a thundercloud to the ground, another cloud, or cloud to ground.

• 28,000oC, 50,400oF

Thunder

• Sound created as lightning “superheats” and it expands (explodes) rapidly.

• Approximately 3 seconds for sound to travel 1 kilometer.

Tornado

• Narrow, funnel shaped column of spiraling winds that extend downward from the cloud base and touches the ground.

• Fujita scale F0-F5, damage related.

Tornado Peak Season

• From late spring to summer. • Occur most frequently in late afternoon.• Temperature lag is the cause. The Earth is

responsible for heating the lower atmosphere.

Waterspouts

• A tornado that has formed over a body of water.

• Usually weaker than a land born tornado.

Severe Thunderstorms

• Has wind gust of at least 80 m.p.h., hail about 2 cm in diameter or greater, and presence of a funnel cloud or tornado.

Watch

• Covers an area of 100km by 200km or larger. Severe t-storms and tornadoes possible.

Warning

• Is issued when a severe thunderstorm or tornado has been spotted.

Hurricane• Intense low-pressure

tropical area with sustained winds of 120kph (74mph) or greater.

• Strong winds and heavy rains produce major damage.

• It has no fronts, powered by evaporation.

• Source regions include Gulf of Mexico, Caribbean Sea and east coast of Africa.

Hurricane Peak Season

• From late summer to early fall.

Storm Surges

• Formed when a hurricane “piles up” water along the shore and blows it inland. Most damaging during high tides.

Eye

• Central area of sinking air, usually 15-20km in diameter.

• No rain, calm winds, high pressure.

Eye Wall

• Area of intense thunderstorms surrounding the eye of the hurricane.

Tropical Cyclones/Typhoons

• Hurricane near equator.

Naming Hurricanes

• Prior to 1953: – Identified by their date.

• From 1953 to 1979: – Given female names, alphabetically.

• 1979 to the present: – Given male and female names, alphabetically.

Blizzard

• A snowstorm with high winds and low temperatures.

Moisture Supply Differences

• In the United States, the midwest-Gulf of Mexico; the west coast-Pacific Ocean; the east cost-Atlantic ocean.

Computer Model

• A copy of the atmosphere in the computer that contains wind, temperature, pressure, humidity, clouds and precipitation.

Geostationary

• Means “stationary” in respects to the Earth.

GOES

• “Geostationary Operational Environmental Satellite” positioned to picture the 50 states.

Doppler Affect

• Effect caused by the movement of light, sound or wind relative to a stationary point. Winds moving toward the radar appear to have a shorter wavelength than particles moving away from the radar source.

Station Model

• National Weather Service based information from each recording station.