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Part 5. Human Activities

Part 5. Human Activities. Chapter 13 Weather Forecasting and Analysis. Introduction. Weather Forecasting – Both Art and Science National Weather Service Began as Army Signal Corps, then National Weather Bureau Part of the National Oceanic and Atmospheric Agency (NOAA)

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Part 5. Human Activities

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  1. Part 5. Human Activities Chapter 13 Weather Forecasting and Analysis

  2. Introduction • Weather Forecasting – Both Art and Science • National Weather Service • Began as Army Signal Corps, then National Weather Bureau • Part of the National Oceanic and Atmospheric Agency (NOAA) • National Centers for Environmental Prediction (NCEP) • Automated Surface Observing Systems (ASOS) • Data acquisition and dissemination • World Meteorological Organization (WMO) • 170 member nations with 10,000 land stations, 7000 ships, 300 buoys, weather satellites, and 1000 weather balloons (twice daily)

  3. A National Weather Service Office

  4. Advanced Weather Interactive Processing System (AWIPS)

  5. An automated weather recording station

  6. Upper atmosphere • Radiosondes, rawinsondes A radiosonde launch

  7. Forecasting methods • Climatological forecasts • Persistence forecasts • Analog approach • Numerical weather forecasting • Types of forecasts • Qualitative forecasts • Probability (PoP) forecasts • Quantitative forecasts

  8. Numerical Modeling and Weather Forecasting (supercomputer-based forecasts) • Analysis phase -- create or update a computer code of a numerical model of the atmosphere • Numerical model -- mathematical model of atmospheric circulation and moisture; includes equations of motion, continuity, energy, etc. • Prediction phase • Start by inputting current and recent atmospheric conditions into the model/computer program • Solve equations to obtain prediction of future atmospheric conditions • Output maps and other prediction products • After some time elapses (hours or days), repeat the process with the latest current data

  9. (a)-(c) = Three numerical models, (d) = Final forecast, (e) = Observed Precipitation forecast Observed precipitation Forecast represents some type of weighted average of the individual forecast maps

  10. 24-hr forecast skill for various NCEP models Forecast results from 1995. Forecasts of heavy precipitation were less accurate than forecast of light precipitation. Here, the EDAS model was most consistently accurate.

  11. 24-hr, 1-in. NCEP precipitation forecast skill average Forecast skill from 1983-1993 for manual forecasts. Winter precipitation forecasts were better than summer forecasts.

  12. MOS Example Forecast skill is steadily improving with time.

  13. Medium range forecasts (MRF) -- 72 hours to a few weeks • Several different numerical models are used to make medium range forecasts • Ensemble forecastingis a forecast in which the predictions from several different computer model forecasts are combined to form an ensemble average

  14. A 10-day ensemble forecast of the 500 mb layer Lower forecast reliability is expected where the model forecasts disagree. Higher forecast reliability is expected where the model forecasts all agree.

  15. Long range forecasts cover times from several weeks to several months or more • Use climatology, statistics, numerical modes, and subjective judgment • Usually involve coupled ocean-atmosphere models • Are produced in the USGS by NOAA’s Climate Prediction Center (CPC)

  16. Weather Maps and Images • Forecasting done by experienced meteorologist • Examination and analysis of many weather charts and models • Surface maps • Large-scale features depicted • Pressure cells, winds, station models

  17. Weather maps are an important part of weather forecasting

  18. Early morning 850 mb maps can be used to predict surface high air temperatures; the surface high temperature is usually about 27° higher than the early morning air temperature at 850 mb in summer (22° in spring and fall, 16° in winter).

  19. 700 mb maps can be used to help forecast cyclogensis and thunderstorm movement

  20. 500 mb maps help with forecasts of cyclone development and movement

  21. An omega high on a 500 mb map

  22. 300 mb and 200 mb maps show the locations of the jet stream and strong jets; these help determine Rossby wave movements

  23. Convergence/divergence associated with jet streaks Slower moving air Faster moving air Slower moving air

  24. Visible satellite image

  25. Infrared image

  26. Water vapor image

  27. Thermodynamic diagrams • Temperature and humidity values plotted • Indicates stability A Stuve diagram

  28. Sounding plotted on a Stuve diagram

  29. Stability as indicated on a Stuve diagram

  30. Lifted index • Thunderstorm potential • Negative values indicative of thunderstorms • K-index • Indicates air mass thunderstorm potential • High positive values (> 15) indicate thunderstorm potential

  31. End of Chapter 13Understanding Weather and Climate4th EditionEdward Aguado and James E. Burt

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