THE BASIS OF PREDICTING THE WEATHER
Weather refers to the condition of the air on earth at a given place and time, and the basis of weather prediction depends on two major atmospheric phenomenon. They are:
1. The heat of the sun causes the air to rise and water to evaporate. The rising warm air comes in contacts the cold air in the upper levels of the atmosphere. When this happens, the water vapor cools present in the air and condenses into tiny suspended droplets called clouds. When these droplets become too heavy to remain suspended, they fall to earth as rain, snow, sleet, or hail. A body of air that has similar properties and move together is an air mass. Tracking such air masses provides clues to the future temperature, moisture level, and air pressure of the area into which they are moving. Weather forecasting depends on this fundamental principle.
2. Air pressure is the weight exerted by the atmosphere on the air. High pressure means that the air pressure is greater than the surrounding areas, and Low Pressure means that air pressure is lesser than surrounding areas. This difference in air pressure results in wind, or moving air. Since air is denser in high-pressure areas, air moves or winds flow from the high-pressure area to a low-pressure area. Clouds that cause rain flow with the wind from a high-pressure area to a low-pressure area. Thus, low pressure indicates rains and high pressure indicates clear skies.
Though these two principles are applicable universally, peculiar local conditions, such as the presence of a large water body or mountains nearby might lead to exceptions to the above principles.
FORECAST THROUGH OBSERVATION
Weather forms by the interplay of natural forces. Observing the world around us with a keen eye and a sharp ear can tell us something about these natural forces at play, and thus help in forecasting the weather. In fact, before the invention of meteorological instruments during the last 200 years, much of the world relied solely on these natural signs to forecast the weather. Though technology has proved much of such weather lore as not conclusive, some of them are sound and is still the basis on which people make weather forecasts.
1. Dry air stirs up dust particles and causes the sky to appear red in the west, during sunset. Air becomes dry when there is high pressure. On the contrary, a red sky in the east during morning means that the dry air has already moved past, and that a low-pressure system that carries moisture is approaching. Similarly, a reddish or pale moon indicates dust in the air, a result of high pressure. However, a bright and sharply focused moon probably indicates that low pressure has cleared out the dust, and low pressure means rain.
2. A rainbow forms when the suns ray refracts from the moisture. Since most major storm fronts travel from west to east, a rainbow in the west means rain is on its way. On the other hand, a rainbow in the east generally indicates that moisture-laden winds have passed and sunny days are ahead.
3. Strong winds indicate differences in air pressure. Major storm fronts or moisture-laden winds travel from west to east. Therefore, strong easterly winds, or winds blowing towards the east indicate approaching rains, and westerly winds, or winds blowing towards the west indicate that the storm front is leaving the area.
4. Plants react to low pressure and moist air, conditions that herald rain. Under such conditions, most plants release their waste and emit strong smells. Swamps release methane, and this scent can be unpleasant. Leaves of oak and maple trees curl, and pine cone scales remain closed. Like plants, wood emits their waste under humid conditions, and when they do so, they smell. All these are indicators of approaching rains.
5. Clouds are a major indicator of the weather. A general indicator is that if clouds are white and high up, the weather would be fine. However, if they are black, low and massed in large clusters, it indicates wet weather and turbulence. Clouds moving in different directions usually indicate bad weather and hail. Cumulonimbus clouds early in the day and developing throughout the day indicates severe weather, and cirrus clouds with long steamers high up in the sky, or altocumulus clouds like mackerel scales indicates bad weather within 36 hours. However, mammatus clouds, formed by sinking air, indicate that thunderstorms are dissipating. Cloud cover on warm nights prevents heat radiation, leading to warmer weather.
6. Animals by nature tend to react more to changes in air pressure than humans do. When storms approach, the air pressure will suddenly drop low. This causes discomfort in the ears of animals. Birds fly low or stop flying to alleviate this discomfort. Large numbers of birds roosting quietly on power lines when they should be flying indicates swiftly falling air pressure. Similarly, Seagulls tend to stop flying and take refuge at the coast if a storm is coming. Cows typically lie down and stay close together if bad weather's on the way and cats tend to clean their ears. Turtles often search for higher ground and ants tend to build their hills with very steep sides when heavy rains are expected.
7. Another indicator of low pressure and consequently approaching rains are smokes. Low pressure causes the smoke to swirl and descend.
FORECAST THROUGH INSTRUMENTS
The invention of various meteorological equipments and the advancement of science and technology enable man to predict the weather with greater accuracy than relying on observations and natural phenomenon. The development of the telegraph and telegraph networks by the mid eighteenth century facilitated weather reports through newspapers and other sources on a regular basis.
Instruments like rain gauges, used to measure the amount of precipitation, and wind gauges, used to find out the direction of the wind have been in existence since the first century BC. Knowing where the wind is coming from gives clues to the temperature and the amount of water in the air moving into an area. For example, winds from the south are often warmer and carry more moisture than winds from the north. Thermometers, which first made its appearance during the 11th century CE, measure the air temperature via the expansion or contraction of a liquid or a metal as the air temperature changes.
The hygrometer, invented in around 1450 CE measures the relative humidity of air. High relative humidity often makes people the most uncomfortable.
The barometer helps in measuring atmospheric pressure, and since its invention in 1643 CE by Evangelista Torricelli have undergone several changes from a mercury-based apparatus to an aneroid cell based apparatus. Since low pressure indicates a chance of rain, and high pressure generally means clear skies, barometers have become an indispensable tool in weather forecasting. Normal air pressure reading vary from 28 to 31, and quick changes in air pressure mean a high intensity change in the weather.
Measuring the speed of the wind is important to determine when moisture-laden winds would strike at a certain place. Sir Francis Beaufort's Beaufort scale, devised in 1805 CE was the first attempts in this direction. The invention of anemometer in 1846 marked a definite improvement and the measurement of wind velocity became easy and accurate.
The discovery of the Doppler Effect in 1842 and subsequently the Doppler radar help meteorologists calculate wind rotations inside of storms like as tornado's and hurricanes. Monitoring this data predicts the possibility of a severe storm producing funnel clouds and damaging winds.
It was with the invention of the Radiosonde by Robert Bureau of France in 1929 that precise knowledge of weather conditions at higher altitudes became available. Radiosondes are small lightweight boxes equipped with weather instruments and a radio transmitter carried high into the atmosphere by a hydrogen or helium-filled balloon that ascends to an altitude of about 30 kilometers before bursting. During the ascent, the instruments transmit temperature, moisture, and pressure data back to a ground station where the data is processed.
In 1922 CE, Lewis Fry Richardson predicted the possibility of numerical weather prediction. However, it was only by 1955 CE, with the discovery of computers that facilitated the vast number of calculations required that practical use of numerical weather prediction began.
The success of the mission to space and the launch of space satellites mean a quantum leap for weather forecasting. The first meteorological satellite, Tiros I, entered the orbit successfully in 1960 CE. In 1976 CE, the United States launched its first geostationary weather satellite. Weather satellites predict weather on a more global scale. They provide information regarding the elevation and strength of the cloud, and the rate at which they develop. Geostationary satellites orbit above a particular area of the Earth identically with the Earth's rotation and shed valuable information on wind speeds and strength of an impending storm front.