Part 5. Human Activities
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Transcript of Part 5. Human Activities
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Part 5. Human Activities
Chapter 13Weather Forecasting and Analysis
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IntroductionWeather 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)
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A National Weather Service Office
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Advanced Weather Interactive Processing System (AWIPS)
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An automated weather recording station
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– Upper atmosphere– Radiosondes, rawinsondes
A radiosonde launch
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Forecasting methods• Climatological forecasts • Persistence forecasts • Analog approach • Numerical weather forecasting
Types of forecasts• Qualitative forecasts • Probability (PoP) forecasts • Quantitative forecasts
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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
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(a)-(c) = Three numerical models, (d) = Final forecast, (e) = Observed
Forecast represents some type of weighted average of the individual forecast maps
Precipitation forecast Observed precipitation
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24-hr forecast skill for various NCEP modelsForecast results from 1995. Forecasts of heavy precipitation were less accurate than forecast of light precipitation. Here, the EDAS model was most consistently accurate.
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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.
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MOS Example
Forecast skill is steadily improving with time.
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Medium range forecasts (MRF) -- 72 hours to a few weeks• Several different numerical models are used
to make medium range forecasts– Ensemble forecasting is a forecast in
which the predictions from several different computer model forecasts are combined to form an ensemble average
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A 10-day ensemble forecast of the 500 mb layer
Higher forecast reliability is expected where the model forecasts all agree.
Lower forecast
reliability is expected
where the model
forecasts disagree.
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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)
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Weather Maps and Images• Forecasting done by experienced
meteorologist– Examination and analysis of many
weather charts and modelsSurface maps• Large-scale features depicted• Pressure cells, winds, station models
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Weather maps are an important part of weather forecasting
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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).
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700 mb maps can be used to help forecast cyclogensis and thunderstorm movement
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500 mb maps help with forecasts of cyclone development and movement
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An omega high on a 500 mb map
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300 mb and 200 mb maps show the locations of the jet stream and strong jets; these help determine Rossby wave movements
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Convergence/divergence associated with jet streaks
Faster moving air
Slower moving air
Slower moving air
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Visible satellite image
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Infrared image
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Water vapor image
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Thermodynamic diagrams• Temperature and humidity values plotted• Indicates stability
A Stuve diagram
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Sounding plotted on a Stuve diagram
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Stability as indicated on a Stuve diagram
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Lifted index• Thunderstorm potential• Negative values indicative of thunderstorms
K-index• Indicates air mass thunderstorm potential• High positive values (> 15) indicate
thunderstorm potential
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End of Chapter 13
Understanding Weather and Climate 4th Edition
Edward Aguado and James E. Burt