WEATHER MAPS AND SEVERE WEATHER

Weather Maps

Predicting the weather is truly a challenge. Very early civilizations attributed control of the wind, rain and thunder to gods whose favor they needed to gain to take care of their crops and their need for water. Just a few thousand years ago, writings show that people attempted to use the positions of the stars as the basis for forecasting the weather. In the early history of our country, Benjamin Franklin created “Poor Richard’s Almanac” that used collected observations from farmers over the years of natural phenomenon like the behavior of animals and phases of the moon to serve as a general guide for weather forecasting. In the spring, farmers needed to know when the danger of frost was past so they could plant their crops. They again needed to know about the chance of frost in the fall so that tender crops could be saved and hardier crops like corn would dry out and then be harvested.

It is still important for farmers to have an accurate forecast of the weather for crop planting and harvesting, but urban populations are also subject to the wiles of the weather, especially severe weather like tornadoes, hurricanes and monsoons. Modern weather forecasting began with more sophisticated scientific instruments such as the thermometer and barometer. Observations of changes in temperature and pressure are crucial to accurate weather forecasting. Today, weather observers at stations all over the world record weather conditions.

Satellite Technology: Transforming Meteorology (01:00)

The weather station observers record changes in barometric pressure and the speed and direction of surface winds. Even prior to man’s entering space, weather satellites were beaming back data from high altitudes to meteorologists who would combine it with lower atmospheric observations to predict the movement of weather systems around the world. They measure precipitation, record the air temperature and determine the humidity. They note the type, amount and height of the cloud cover, record visibility and general weather conditions. Local meteorologists download information from national and regional observation sites and combine that data with local observations to determine a forecast of 24 hours to five days in scope.

In order to predict the chance of rain or a hazy, hot and humid summer day, meteorologists prepare weather maps at the centers where coded weather information is received. These maps are constantly being updated as new data is received. Weather observations from the various stations reporting to the center are first translated into internationally recognized symbols. Clusters of symbols are plotted on the map around each reporting station, showing the conditions at that station. These symbols at the reporting station on a map are called a STATION MODEL. The common symbols that are used are illustrated in the following chart:

(above) A typical weather map

Notice that the symbols for cloud cover, wind speed, and wind direction are combined into one symbol. One of the indicators included in the station model is the DEW POINT. The dew point is the temperature to which the air must be cooled to become saturated with water vapor. When the air is nearly saturated, there is a difference between its temperature and the dew point. A comparison of these is an indication of the RELATIVE HUMIDITY.

This station model also indicates the atmospheric pressure in MILLIBARS. The position of a straight line under this number shows whether the atmospheric pressure is steady, rising or falling.

You will notice on the weather map that lines have been drawn that connect points of equal atmospheric pressure. These are called ISOBARS. The spacing and shape of the isobars help meteorologists interpret their observations about the speed and direction of the wind. Closely spaced isobars indicate a rapid change in pressure and high wind speeds. Widely spaced isobars generally indicate a slow change in pressure and low wind speeds. Isobars that form circles indicate where there are centers of high (H) or low (L) pressure. For instance, closely spaced isobars that form concentric circles around a low pressure center represent a storm system.

The weather map is completed by marking in the location of fronts and areas of precipitation. FRONTS are definite boundaries of air masses of different temperatures. Fronts are indicated by changes in winds, temperature or humidity.

When meteorologists give the weather report, not only do they show these weather maps and pinpoint information collected at these stations, but now have the ability to show animated, computerized graphics to illustrate how they are predicting a system will move through an area. Local DOPPLER RADAR SYSTEMS continuously feed information to local meteorologists who may now pinpoint weather headed to a particular location at a particular time. Continuous accurate forecasts can usually be made for two to three days but, even with modern technology, accuracy decreases with each additional day of forecast length.

Click on the following link to find the National Doppler Radar Site in your area. https://radar.weather.gov/

Meteorologists Use Scientific Intruments to Measure and Predict Weather

Visit MSN Weather, type in your zip code to find the weather in your area http://weather.msn.com/.

Severe Weather

Meteorology is the study of the earth’s atmosphere. One job of a meteorologist is to study the information collected about the atmospheric conditions and use it to predict the weather. Listening to the weather report allows you to know how warmly to dress, or if your picnic plans need to be re-directed indoors!

Sometimes the conditions of the atmosphere are such that severe weather may occur. The collision of air masses to form fronts may spawn severe storms like hurricanes, tornados and monsoons. HURRICANES are severe tropical storms with winds as strong as 150 miles/hour. Hurricanes develop over warm, tropical oceans near the equator. Their winds spiral inward towards the storm center known as the EYE. This area is deceptively calm and clear compared to the violence and energy of the other part of the hurricane. A hurricane begins when very warm, moist air over the ocean rises rapidly. When moisture in the rising warm air condenses, a large amount of energy in the form of latent heat is released. This heat increases the force of the rising air. Moist tropical air continues to be drawn into the column of rising air. More heat is released and the process becomes self-sustaining. The entire storm system spins as a result of the CORIOLIS EFFECT, a deflection of the earth’s wind and ocean currents caused by the earth’s rotation. The average amount of energy content of a hurricane can be compared to the energy content of the total amount of electricity used in the United States for six months! Once a hurricane has fully developed, it consists of a series of thick cloud bands spiraling upward into the center of the storm. Rainfall is extremely heavy. The winds of a hurricane usually persist anywhere from 9-12 days. Even though viewed from space it may appear as a massive thing of beauty, the destruction it brings if it comes on land is tremendous.

Two devastating hurricanes hit the state of Florida within three years and traveled up the eastern seaboard of the United States. Hurricane Andrew, which occurred in 1992, destroyed 90% of Homestead, Florida, and caused damages of $22 billion. Hurricane Hugo hit Florida in 1989, causing $5 billion in damages. Weather forecasters can track hurricanes and their path for days allowing them to warn the public so evacuation and storm preparations can occur. If a hurricane forms over the Pacific Ocean, it is referred to as a TYPHOON.

A much more difficult storm for weather forecasters to predict is the tornado. TORNADOS are whirling, funnel-shaped cyclones that are relatively short lived compared to hurricanes. The National Weather Service may issue a STORM WATCH which means conditions are favorable for a storm and giving citizens an hour or more of preparation time. A TORNADO WARNING is issued once a funnel cloud has been seen on the ground. A local area may have a siren warning system to indicate a tornado has been spotted, but residents may only have a few minutes or seconds to seek shelter once this has been sounded.

A tornado forms when a thunderstorm meets high altitude, horizontal winds. These winds cause the rising air in the thunderstorm to rotate. One of the storm clouds may develop a narrow, funnel-shaped, rapidly spinning extension. Exactly how a funnel forms is not completely understood and is the subject of constant research. Meteorologists use instrumentation readings, as well as first hand observations from storm chasers. Storm chasers monitor weather conditions and actually seek out storms that may produce funnel clouds. They are the front line of defense when it comes to issuing a storm warning. Their observations of the behavior of the storm help meteorologists to better understand the formation of a funnel cloud. This would allow better warning systems to be developed for the public, giving them more time to seek safe shelter.

The destructive power of a tornado is due to the speed of the whirling winds within the funnel. Their great destructive power indicates that wind speeds may reach 300 miles/hour. The most common occurrence of tornados is in the Midwestern United States during the late spring or early summer. Their severity is ranked on the FUJITA SCALE listed below. Tornados that occur over the ocean are called WATERSPOUTS and are usually smaller and less powerful than tornados occurring over land.

THE FUJITA SCALE
SCALE	WIND ESTIMATE (miles/hr)	TYPICAL DAMAGE
F0	40-72	Light damage. Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.
F1	73-112	Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads.
F2	113-157	Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
F3	158-206	Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.
F4	207-260	Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.
F5	261-318	Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur.

Heat differences that occur between the land and the oceans sometimes cause the winds to shift seasonally in certain regions. During the summer, the sun’s energy causes the land to heat more quickly than the ocean. If a low-pressure center develops over the land, this allows the warm air to rise and be replaced by cool air from the ocean. Thus the wind moves toward the land. During the winter, the land loses heat more quickly than the ocean does, and the cool air flows away from the land. Thus the wind moves in the opposite direction- toward the sea. These seasonal winds are called MONSOONS. These winds are strongest over the large landmasses near the equator. For example, monsoons in southern Asia result from the heating and cooling of the northern Indian peninsula. In the summer, winds carry moisture to the land from the ocean, bringing heavy rainfall. In the winter, winds bring dry weather, sometimes even drought. Monsoon conditions also occur in eastern Asia and in equatorial regions with long coastlines.

The following videos contain footage of severe storm situations such as powerful thunderstorms and lightning, tornadoes, and hurricanes.

Thunderstorms

Tornadoes (02:39)

Hurricanes (01:50

Now answer questions 1 through 15.