Weather Forecasting

1
Weather Forecasting

• Chapter 9

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Acquisition of Weather Information

• 10,000 land-based stations, hundreds of ships and
  buoys four times a day, airports hourly
• Upper level radiosonde, aircraft, satellites
• United Nations World Meteorological Organization,
  175 countries
• World Meteorological Centers Melbourne, Moscow,
  Washington D.C.
• NCEP, US NWS
• ASOS

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Weather Forecasting Tools

• Topic Watches, Warnings, and Advisories
• Advisories potential hazardous conditions wind,
  wind chill, heat, urban and small stream, snow,
  dense fog
• Watch atmospheric conditions favoring hazardous
  weather over a region in time, actual location
  and time not known flash flood, severe
  thunderstorm, tornado, hurricane
• Warning imminent or occurring hazardous weather
  over a region in time high wind, heat, flash
  flood, severe storm, tornado, hurricane, winter
  storm, blizzard, gale, storm

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Weather Forecasting Tools

• High speed data modeling systems (AWIPS)
  communication, storage, processing, and display
• Doppler radar
• Satellite imagery
• Forecast charts
• Soundings
• Meteograms
• Wind profiles

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Fig. 9-1, p. 247
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Fig. 9-2, p. 247
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Fig. 9-3, p. 249
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Fig. 9-4, p. 250
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Weather Forecasting Tools

• Satellite Observations
• Geostationary, polar orbiting
• Visible light provides a black and white picture
  of clouds
• Infrared approximates cloud temperature which
  infers height
• Satellites measure many other variables sea
  surface temperatures, ozone, upper level
  features, snow cover, land cover

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Fig. 9-5, p. 250
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Fig. 9-6, p. 251
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Fig. 9-7, p. 251
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Fig. 9-8, p. 252
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Fig. 9-9a, p. 252
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Fig. 9-9b, p. 252
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Fig. 9-10, p. 253
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Fig. 9-11, p. 253
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Fig. 9-12, p. 254
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Weather Forecasting Methods

• 1950s maps, charts plotted by hand
• Numerical weather prediction Computer Model
• Solves equations using gridded data
• Final chart called analysis
• 24 hr forecast for the N Hemisphere requires
  millions of calculations
• Resolution
• Guidance/ rules of thumb

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Fig. 9-13, p. 255
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Fig. 9-13a, p. 255
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Fig. 9-13b, p. 255
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Fig. 9-14, p. 255
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Weather Forecasting Methods

• Why Forecasts Go Awry
• Assumptions
• Models not global
• Regions with few observations
• Cannot model small-scale features
• All factors cannot be modeled
• Ensemble Forecasts
• Spaghetti model, robust
• Observation Weathercasters
• Chroma key or color separation

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Fig. 9-15, p. 257
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Weather Forecasting Methods

• Other Forecasting Techniques
• Persistence Tomorrow Like Today
• Trend Current Change will Continue
• Analogue Find current conditions in the
  past
• Statistical Probability of occurence
• Weather type
• Climatological Based on an areas climate

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Table 9-1, p. 259
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Fig. 9-16, p. 260
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Fig. 9-17, p. 261
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Weather Forecasting Methods

• Types of Forecasts
• Now cast lt6 hrs
• Short range 12-65 hrs
• Medium range 3-8.5 days
• Long Range gt8.5 days
• Accuracy and Skill
• 12-24 hrs most accurate, 2-5 days good
• Skill more accurate than a forecast utilizing
  persistence of climatology

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Fig. 9-18, p. 262
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Fig. 9-18a, p. 262
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Fig. 9-18b, p. 262
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Weather Forecasting Using Surface Charts

• Movement of Weather Systems
• Mid-lat cyclones move in same direction and speed
  as previous 6 hrs
• Lows move in direction parallel the isobars in
  the warm air ahead of the cold front
• Lows move toward region of greatest pressure drop

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Table 9-2, p. 265
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Weather Forecasting Using Surface Charts

• Forecast
• August GA
• Washington DC
• Chicago
• Memphis
• Dallas
• Denver

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Fig. 9-20, p. 266
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Fig. 9-21, p. 267
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Fig. 9-22, p. 267
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Stepped Art
Fig. 9-22, p. 267
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Fig. 9-23, p. 269