Transcript Wind: Global Systems

Chapter 9
Acquisition of Weather
Information
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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
Weather Forecasting Tools
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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
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
Fig. 9-2, p. 247
Fig. 9-3, p. 249
Fig. 9-4, p. 250
Weather Forecasting Tools
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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
Fig. 9-5, p. 250
Fig. 9-6, p. 251
Fig. 9-7, p. 251
Fig. 9-8, p. 252
Fig. 9-9a, p. 252
Fig. 9-9b, p. 252
Fig. 9-10, p. 253
Fig. 9-11, p. 253
Fig. 9-12, p. 254
Weather Forecasting Methods
1950s maps, charts plotted by hand
 Numerical weather prediction: Computer Model
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 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
Fig. 9-13, p. 255
Fig. 9-13a, p. 255
Fig. 9-13b, p. 255
Fig. 9-14, p. 255
Weather Forecasting Methods
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Why Forecasts Go Awry
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Assumptions
Models not global
Regions with few observations
Cannot model small-scale features
All factors cannot be modeled
Ensemble Forecasts:
 Spaghetti model, robust
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Observation: Weathercasters
 Chroma key or color separation
Fig. 9-15, p. 257
Weather Forecasting Methods
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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
Table 9-1, p. 259
Fig. 9-16, p. 260
Fig. 9-17, p. 261
Weather Forecasting Methods
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Types of Forecasts
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Now cast <6 hrs
Short range 12-65 hrs
Medium range 3-8.5 days
Long Range >8.5 days
Accuracy and Skill
 12-24 hrs most accurate, 2-5 days good
 Skill = more accurate than a forecast utilizing
persistence of climatology
Fig. 9-18, p. 262
Fig. 9-18a, p. 262
Fig. 9-18b, p. 262
Weather Forecasting Using
Surface Charts
Movement of Weather Systems
1. Mid-lat cyclones move in same direction
and speed as previous 6 hrs
2. Lows move in direction parallel the
isobars in the warm air ahead of the cold
front
3. Lows move toward region of greatest
pressure drop
Table 9-2, p. 265
Weather Forecasting Using
Surface Charts
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Forecast
 August GA
 Washington DC
 Chicago
 Memphis
 Dallas
 Denver
Fig. 9-20, p. 266
Fig. 9-21, p. 267
Fig. 9-22, p. 267
Stepped Art
Fig. 9-22, p. 267
Fig. 9-23, p. 269