Transcript Volcanoes and Igneous Activity Earth

Chapter 12: Weather Analysis and Forecasting
The Atmosphere:
An Introduction to
Meteorology, 12th
Lutgens • Tarbuck
Lectures by:
Heather Gallacher,
Cleveland State University
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The Weather Business: A Brief Overview
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National Weather Service (NWS) is a branch of the
National Oceanic and Atmospheric Administration
(NOAA).
The mission statement of NWS is to provide
weather and climate forecasts and warnings to the
U.S., territories, and waters for the protection of life
and property and enhancement of the economy.
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The Weather Business: A Brief Overview

National Centers for Environmental Prediction:
 This branch of the NWS collects weather data from all
over world.
 Information is disseminated to 125 regional Weather
Forecast Offices, which prepare local forecasts.
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Weather Analysis
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Weather analysis:
 The forecaster must collecting, transmit, and compile
billions of pieces of observational data.
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Weather Analysis
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Gathering data:
 The World Meteorological Organization (WMO), which is
part of United Nations is responsible for the international
exchange of weather data.
 Surface observations:
 The NWS and the Federal Aviation Administration (FAA)
operate ~900 automated surface observation systems (ASOS).
 Worldwide, more than 10,000 land observation stations, 7000
ships at sea, and hundreds of data buoys and oil platforms
report conditions four times daily.
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Weather Analysis
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Weather Analysis
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Observations aloft:
 Weather balloons are launched twice daily at midnight and
noon GMT.
 They contain radiosondes, which are lightweight instrument
packs measuring temperature, humidity, and pressure.
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Weather Analysis
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Weather maps: pictures of the atmosphere
 The collected information is displayed in a format that can
be comprehended easily by forecasters.
 The information is placed on synoptic weather maps, which
means “coincident in time.”
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Weather Forecasting Using Computers
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Numerical weather prediction:
 This technique uses mathematical models.
 It begins by entering temperature, wind speed and
direction, pressure, and humidity.
 The NWS produces generalized forecast maps, called
prognostic charts (or progs).
 A statistical analysis of progs compares the accuracy of
previous forecasts.
 This approach is known as Model Output Statistics (MOS).
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Weather Forecasting Using Computers
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Ensemble forecasting:
 This method produces a number of forecasts using the
same computer model.
 It alters initial conditions while remaining within error
range of the observational instruments.
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Weather Forecasting Using Computers
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Role of the forecaster:
 After progs are sent to the WFOs, forecasters blend
information with local conditions and regional weather
to produce site-specific forecasts.
 Forecasters use their knowledge and judgments based
on experience.
 They will sometimes add extra detail to the model
forecasts.
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Other Forecasting Methods
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Persistence forecasting:
 This technique is based on the tendency of weather to
remain unchanged for hours or days.

Climatological forecasting:
 This method uses climate data (average weather statistics
over many years).
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Other Forecasting Methods
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Other Forecasting Methods
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Analog method:
 This is based on the assumption that weather repeats itself.
 Forecasters attempt to find weather patterns.
 Pattern recognition is an important tool, which helps
improved short-range, computer-generated forecasts.
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Trend forecasting:
 This method determines the speed and direction of fronts,
cyclones, clouds and precipitation.
 Forecasters try to extrapolate the future position of
weather phenomena.
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Upper Airflow and Weather Forecasting
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Upper level maps:
 These maps are generated twice daily.
 They are drawn at 850-, 700-, 500-, 300-, and 200-millibar
(mb) levels.
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Upper Airflow and Weather Forecasting
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850- and 700-millibar
maps:
 The 850-mb map finds
areas of cold-air and
warm-air advection.
 Winds at the 750-mb
level are used to predict
movement of weather
producers.
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Upper Airflow and Weather Forecasting
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500-mb maps:
 This level if found approximately 5.5 km above sea level.
 These maps show upper level lows best.
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Upper Airflow and Weather Forecasting
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300- and 200-mb maps:
 These maps represent zones near the top of
the troposphere.
 The jet stream is best observed at these levels.
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Upper Airflow and Weather Forecasting
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The connection between upper-level flow and
surface weather:
 Zonal patterns depict quickly moving westerlies (west to
east).
 Meridional patterns consist of slow moving north to south
flows, typically with heavy precipitation.
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Upper Airflow and Weather Forecasting
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Upper Airflow and Weather Forecasting
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An extreme winter
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Upper Airflow and Weather Forecasting
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Long-range forecasts:
 The Climate Prediction Center, a branch of the NWS,
produces 30- and 90-day outlooks.
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Forecast Accuracy
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Percentage probability:
 Rainfall is the only aspect of a forecast expressed this way.
 The prediction of occurrence is fairly accurate.
 The predictions of amount, time, and duration are not
as reliable.
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Short- and medium-range forecasts:
 Accuracy has improved over the decades.
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Beyond 8 days:
 Predictability of day-to-day weather is of low accuracy.
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Satellites in Weather Forecasting
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TIROS 1:
 Launched in 1960, this was the first weather satellite.
 Since then, more than 30 versions have been launched
through 2009.
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Polar-orbiting:
 These satellites orbit over the poles.

Geostationary:
 These satellites orbit west to east over the equator.
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Satellites in Weather Forecasting
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Satellites in Weather Forecasting
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What types of images do weather satellites provide?
 Geostationary Operational Environmental Satellites
(GOES) provide visible, infrared, and water-vapor images.
 They track large weather systems.
 Visible light imagery records the intensity of light reflected
from cloud tops and other surfaces, to help define shapes,
patterns, and thicknesses.
 Infrared images are obtained from radiation emitted
from objects.
 They help to determine which clouds are likely to produce
heavy precipitation.
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Satellites in Weather Forecasting
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Satellites in Weather Forecasting
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Visible:
 Only during day
 Higher resolution
 No temperatures
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Infrared:
 Day or night
 Shows temperature of
cloud tops
 Lower clouds—warmer
 Higher clouds—cooler
Satellites in Weather Forecasting
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Water-vapor images:
 Most of Earth’s radiation with a wavelength of
6.7 micrometers, is emitted by water vapor.
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End Of Chapter 12
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