Weather Prediction


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Weather maps & Station Models

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  • In a radar unit, a transmitter emits radio waves at a rate of about 500 per second. As those waves encounter objects, they bounce off of them and head back towards the radar unit. A receiver in the radar unit then records when the bounced signals return. The time that it takes for the radio waves to travel to an object and then bounce back indicates how far away the object is. In addition, differences between the outgoing and returning waves provide information about the makeup of the object. Weather radar, for example, can determine whether a cloud is made up of ice crystals (a cold cloud) or water droplets (a warm cloud). If the radar unit is slowly turned in a circle so that it sends out waves in all directions, it can provide a good view of the surrounding area. Sound waves                                      radio waves longitudinal                                          transverse low speed (340m/s)                            high speed (almost equivalent to the speed of light) high wavelength                                  small wavelength low frequency                                      high frequency
  • Doppler radar is relatively new for meteorologists, but it is a well-known tool in law enforcement. This radar uses the Doppler effect, which you will learn about in a later module. The Doppler effect says that by analyzing a specific kind of difference (the wavelength) between the outgoing and returning waves, the speed of the object being observed can actually be determined. Traffic police use Doppler radar to determine the speed of automobiles, while meteorologists use it to measure the speed of distant winds. Meteorology probably made its greatest step forward when satellites were deployed for weather-related measurements. The first weather satellite, TIROS I, was launched in 1960. Today, there are close to 50 weather satellites circling the globe, taking constant measurements of the kinds of data I mentioned above. They give us an accurate, global picture of the weather fronts and patterns that exist on a day-to-day basis.
  • Notice the thin black lines that are drawn all around the map. These lines are isobars and represent regions of equal atmospheric pressure. If you travel along a single isobar, the atmospheric pressure does not change. Notice how between Houston and Miami the isobars form irregular ovals and at the center is a large “H.” That “H” tells you that the isobar surrounding it represents high pressure. As you move away from the “H,” each isobar represents a lower pressure. Thus, the atmospheric pressure in Miami is higher than the atmospheric pressure in Houston because Miami is between the first and second isobar away from the “H,” while Houston is just past the second isobar. Thus, Houston is more isobars away from the “H” and therefore has lower atmospheric pressure. Chicago and Indianapolis, however, have similar atmospheric pressures because they are very near the same isobar. Look at the “L” centered over the New England area. This tells us that the isobar surrounding the “L” represents the lowest atmospheric pressure. Each isobar moving outward from that “L” represents areas with increasing atmospheric pressure. Thus, we can tell the general atmospheric pressure of a region by looking at such a map and reading the isobars.
  • Weather stations record data Info displayed on maps
  • Example: 20 knots from the northeast
  • In weather forecasting, all of that information gets put into a computer and mathematical models predict where weather fronts will move and how quickly. The people interpreting the results decide, based on the characteristics of the weather fronts, what kind of weather is likely. Since we know so little about weather, these forecasts are not able to predict the weather accurately. Instead, they predict the percentage chance of weather events. For example, a weather forecast might say that there is a 30% chance of rain tomorrow. This forecast means that most likely, there will not be rain tomorrow. Nevertheless, it is possible for it to rain. Not very accurate, is it? Nevertheless, today's weather forecasting is significantly more accurate than it used to be!
  • Weather Prediction

    2. 2. RADAR <ul><li>Radio Detection And Ranging </li></ul><ul><ul><li>500 radio waves per second emitted </li></ul></ul><ul><ul><li>waves bounce off clouds/objects </li></ul></ul><ul><ul><li>receiver records returning signals </li></ul></ul>
    3. 3. <ul><li>Doppler Radar </li></ul><ul><ul><li>Used by police to track vehicle speeds </li></ul></ul><ul><ul><li>Used by meteorologists to measure wind speeds </li></ul></ul><ul><li>Weather Satellites </li></ul><ul><ul><li>TRIOS I was first launched in 1960 </li></ul></ul><ul><ul><li>Record visible and infrared (thermal) light </li></ul></ul><ul><ul><li>Track clouds/hurricanes, fires, effects of pollution, auroras, sand and dust storms, snow cover, ocean currents, etc. </li></ul></ul>
    4. 4. Weather Maps
    5. 5. Surface Weather Maps <ul><ul><li>H = cool, dry air with fair weather & light clockwise winds (NH) </li></ul></ul><ul><ul><li>L = warm, wet air with stormy weather & high counter-clockwise winds </li></ul></ul><ul><li>Pressure </li></ul><ul><li>Fronts </li></ul><ul><li>Precipitation </li></ul>
    6. 6. Isobars <ul><li>Lines represent areas of equal atmospheric pressure </li></ul>
    7. 7. <ul><li>Closer lines indicate quicker change in pressure </li></ul><ul><li>Greater range of pressure = stronger winds </li></ul><ul><li>Air moves from high pressure to areas of low pressure </li></ul>Pressure Gradients
    8. 8. Wind Direction <ul><li>High pressure centers push out (faster at edge) </li></ul><ul><li>Low pressure centers allow air to move inward (faster near center) </li></ul><ul><li>Rotation is caused by Coriolis Effect </li></ul>Clockwise (NH) Counter -Clockwise (NH)
    9. 10. Station Models Weather station data displayed using internationally-accepted symbols
    10. 11. Cloud Cover
    11. 12. Wind Speed & Direction
    12. 13. Precipitation (Weather)
    13. 14. Temperature & Dew Point <ul><li>Temperature in U.S. recorded in degrees Fahrenheit </li></ul><ul><li>Dew point is the temperature at which atmospheric water vapor condenses into liquid </li></ul>
    14. 15. Isotherms <ul><li>Lines or colors each represent an area of equal temperature </li></ul>
    15. 16. <ul><li>Top # shows atmospheric pressure in millibars </li></ul><ul><ul><li>ranges from 987 to 1050 mb </li></ul></ul><ul><ul><li>9 or 10 omitted in station model </li></ul></ul><ul><li># below shows the amount of future change </li></ul><ul><li>Line shows direction of change </li></ul>Barometric Pressure
    16. 17. Station Model Maps <ul><li>Cloud Cover </li></ul><ul><li>Wind </li></ul><ul><ul><li>direction </li></ul></ul><ul><ul><li>speed </li></ul></ul><ul><li>Temperature </li></ul><ul><ul><li>current temp. </li></ul></ul><ul><ul><li>dew point </li></ul></ul><ul><li>Precipitation </li></ul><ul><li>Pressure </li></ul><ul><ul><li>current pressure </li></ul></ul><ul><ul><li>direction of change </li></ul></ul><ul><ul><li>millibars of change </li></ul></ul>
    17. 18. What's the Weather?
    18. 19. Cumulus Clouds
    19. 21. Forecasting <ul><li>Computer programs analyze data </li></ul><ul><ul><li>use mathematical formulas to create &quot;models&quot; </li></ul></ul><ul><ul><li>give predictions as percentages </li></ul></ul><ul><ul><ul><li>i.e. 30% chance of rain today, slight chance of snow </li></ul></ul></ul><ul><ul><li>accuracy low for more than 3 days in future </li></ul></ul>