Geology Ch.19 - Weather Patterns and Severe Storms

Define hurricane. What other names are used for this storm?

A hurricane is a strong storm that forms over tropical waters and has a deep low-pressure center and high, sustained winds. Hurricanes are also called typhoons and cyclones.

Why do hurricanes not form near the equator? Explain the lack of hurricanes in the South Atlantic and eastern South Pacific.

A hurricane is large storm that rotates due to the Coriolis effect; there is no Coriolis effect near the equator. There are no hurricanes in the South Atlantic or the eastern South Pacific because the ocean waters are too cold and hurricanes require warm, deep waters to form.

Describe a stationary front and an occluded front.

A stationary front is when a front is not moving and airflow is almost parallel to the line of the front. An occluded front is when a cold front overtakes a warm front and acts as a boundary between two different types of air.

Distinguish between a tornado watch and a tornado warning.

A tornado watch is issued when conditions are right for the possibility of tornadoes occurring. A tornado warning is issued by the local National Weather Service office when a tornado has been spotted in person or on radar.

Briefly compare and contrast midlatitude cyclones, hurricanes, and tornadoes. How are thunderstorms related to each?

All three of these storms have a low-pressure center and cyclonic airflow. Midlatitude cyclones are the largest of these storms, with diameters up to 1000 miles and tornadoes are the smallest, with diameters far smaller than a half mile. Thunderstorms can form in conjunction with cyclones, tornadoes can be spawned from them, and hurricanes can generate thunderstorm activity in a wide area.

Define air mass. What is air mass weather?

An air mass is a large body of air with similar temperature and moisture characteristics. Air-mass weather is when an area experiences fairly consistent weather over a period of several days due to the length of time it takes for a large air mass to move through the region.

During what months is tornado activity most pronounced in the United States?

April through June.

In what latitude zone do hurricanes develop?

Between 5° and 20° latitude over tropical oceans.

Compare the temperature and moisture characteristics of the following air masses: cP, mP, mT, and cT.

Both mP and mT air masses will be humid, but mT will be warm and mP will be cool. In contrast, cP and cT air masses will both be dry, but cP will be cold and cT will be hot.

Why is cold-front weather usually more severe than warm-front weather?

Cold fronts move more quickly than warm fronts and they approach at a steeper angle, causing more rapid uplift of air and storm generation.

Why does the intensity of a hurricane diminish rapidly when it moves over land?

Hurricanes require warm, moist air over warm oceans to sustain themselves; when they move over land, they lack fuel to be sustained.

Briefly explain how flow aloft aids the formation of cyclones at the surface.

If flow aloft is diverging above a low-pressure system at the surface, it causes rising air within the low. Air then flows into the low pressure at the surface, contributing to sustaining this cyclone.

Which air mass is associated with lake-effect snow? What causes lake-effect snow?

Lake-effect snow is associated with the cP air mass. Lake-effect snow generally occurs in late fall or early winter when the dry cP air mass moves across relatively warm Great Lakes waters. The air gains a great deal of heat and moisture, generating humid, unstable air that brings heavy snow to the land over which the air mass moves next.

What is the source of energy that drives a hurricane?

Latent heat from condensation of water over tropical oceans.

When do most hurricanes in the North Atlantic and Caribbean occur? Why are these months favored?

Most hurricanes form in the late summer months, when ocean temperatures are warm enough for hurricane formation.

Where are thunderstorms most common on Earth? In the United States?

On Earth, thunderstorms are most common in the tropics. In the United States, Florida has the most thunderstorm activity.

What general atmospheric conditions are most conducive to the formation of tornadoes?

Severe thunderstorms associated with cold fronts.

What are the three broad categories of hurricane damage?

Storm surge, wind damage, and heavy rains with inland flooding.

If the midlatitude cyclone described in Question 1 took 3 days to pass your location, on which day would temperatures likely be warmest? On which day would they likely be coldest?

Temperatures would likely be warmest on day 2. It would be coldest on day 3.

Name the scale commonly used to rate tornado intensity. How is a rating on the scale determined?

The Enhanced Fujita intensity scale. A rating is determined by assessing the worst damage caused by the tornado.

Summarize the stages in development of a thunderstorm.

The cumulus stage is marked by updrafts and building of the cloud. The mature stage has heavy precipitation and updrafts and downdrafts. The dissipating stage is where downdrafts predominate and precipitation gradually stops.

Distinguish between the eye and the eye wall of a hurricane. How do conditions differ in these zones?

The eye is the center of the hurricane and is marked by its lack of winds and precipitation. The eye wall is just around the eye and marks the region of the highest sustained winds and heaviest precipitation in the storm.

Why do tornadoes have such high wind speeds?

There is a very strong pressure gradient associated with a tornado.

What winter weather might be expected with the passage of a mature midlatitude cyclone when the center of low pressure is located about 100 to 200 kilometers (60 to 125 miles) south of your location?

There would first be a steady air pressure drop, overcast conditions, and probably snow. As an occluded front forms in this area, there is a low-pressure counterclockwise rotation of air that can persist for a week, keeping poor weather, clouds, and snow in the region during this time.

Briefly describe the weather associated with the passage of a mature midlatitude cyclone when the center of low pressure is about 200 to 300 kilometers (125 to 200 miles) north of your location.

There would first be cirrus clouds and then would come lower, thicker clouds and falling air pressure. Precipitation would increase as would the temperature as the warm front associated with the cyclone passes. A cold front follows, bringing gusty winds and heavy precipitation that could possibly bring severe storms as well. After the cold front moves through, skies will clear.

On what basis are air masses classified?

They are classified based on their source regions

Compare the weather of a typical warm front with that of a typical cold front.

Warm fronts cause a gradual increase in temperature as they move into an area and typically produce light or moderate precipitation. Cold fronts tend to cause a rapid decrease in temperature and are often associated with heavy rains and thunderstorms.

What are the basic requirements for the formation of a thunderstorm.

You need warm, moist, unstable air and an air uplifting mechanism.