Weather Forecasting by shitingting


									Weather Forecasting

       Yean Lee Low
    6th December 2010

•   Introduction
•   Objective of Weather Forecasting
•   What Types of Weather Forecasting Exists?
•   The Makings Of A Weather Forecast
•   Limits In Weather Forecasting
•   Sources


What is weather?
• Weather is the state of the atmosphere, to the
  degree that it is hot or cold, wet or dry, calm or
  stormy, clear or cloudy (According to Wikipedia)

What is forecasting?
• Forecasting is a process which has as its
  objective the prediction of future events or
  conditions. More precisely, forecasting attempts
  to predict change (Hans Levenbach)            3/29

What is weather forecasting?
• Weather forecasting is the application of
  science and technology to predict the state of
  the atmosphere for a future time and a given
  location (According to Wikipedia)

Objective of Weather Forecasting

• Weather alerts and advisories - serious
  thunderstorm, tornado and flood warning
• Air traffic -Fog can prevent many aircraft
  from landing and taking off.
  Thunderstorms, strong winds, and
  lightning, all of which can cause serious
  damage to an aircraft in flight. Volcanic
  ash a significant problem, as aircraft can
  lose engine power within ash clouds.
Objective of Weather Forecasting

• Marine - Important to fisherman especially
  weather in the sea – wind, waves

• Agriculture -Farmers rely on weather
  forecasts to decide what work to do on
  any particular day. Prolonged periods of
  dryness can ruin cotton, wheat, and corn
 What Types of Weather Forecasting
Weather forecasts for can be grouped into:
• Short range forecast (up to 48 hours)

• Extended forecast (up to 5 days)

• Long range forecast (30days to the season)

 The Makings Of A Weather Forecast
• Assess current weather situation (“Initial
 - Before we can look into future, understand what
 is happening now
• Digest observational information (“Data
 - Bring observed data into “standard” format
 The Makings Of A Weather Forecast
• Project initial state into future
  (“Numerical Weather Prediction” (NWP)
  model forecasting )
  - Based on laws of physics
• Apply weather forecast information
  (“User applications”)
  - Statistical post-processing

      Observing The Current State –
              Surface-Based Systems
Land surface - SYNOP station
SYNOP (surface synoptic observations) is a numerical code
(called FM-12) used for reporting weather observations
made by manned and automated weather stations. SYNOP
reports are typically sent every six hours on shortwave
using Radioteletype. A report consists of groups of numbers
(and slashes where data is not available) describing general
weather information, such as the temperature, barometric
pressure and visibility at a weather station.

           Observing The Current State –
                             Surface-Based Systems

                                    General structure of a SYNOP message

   SYNOP station
              Observing The Current State –
                                     Surface-Based Systems

SYNOP decoder Active/X - This Active/X package has been written in C language to
deliver a very high processing speed. It has been designed to decode the SYNOP
messages.                                                 12/29
      Observing The Current State –
              Surface-Based Systems
Ocean – buoy
Weather buoys are instruments which collect weather and
ocean data within the world's oceans. They measure
parameters such as air temperature at the ocean surface,
water temperature, wave height, dominant wave period,
barometric pressure, wind speed, and wind direction. The
buoys transmit this data via satellite communications to
meteorological centers for use in weather forecasting and
climate study. Weather buoys can always be recognized by
their yellow color and flashing yellow light at night.

             Observing The Current State –
                                Surface-Based Systems

Weather buoy                                Example of Buoy data.

      Observing The Current State –
  Remotely Sensed “IMAGES”, Instead Of “DATA POINTS”

Remote sensing can be defined as the collection of data
about an object from a distance. Geographers use the
technique of remote sensing to monitor or measure
phenomena found in the Earth's. Remote sensing of the
environment by geographers is usually done with the help
of mechanical devices known as remote sensors. These
gadgets have a greatly improved ability to receive and
record information about an object without any physical
contact. Often, these sensors are positioned away from the
object of interest by using helicopters, planes, and

            Observing The Current State –
    Remotely Sensed “IMAGES”, Instead Of “DATA POINTS”

 • Satellite imagery   16/29
       Observing The Current State                                 –
  Remotely Sensed “IMAGES”, Instead Of “DATA POINTS”

• Wind speed ( Radar)
  Information on the movement of objects either toward or away from the
  radar can be used to estimate the speed of the wind.

   Radar                  Example of wind speed image taken from Radar
       How Observations Are Used?
   Data Must Be Moulded Into “MODEL” Standard Format

Data assimilation
• Data assimilation is a concept involve any method for
  combining observations of variables like temperature,
  and atmospheric pressure into numerical models as the
  ones used to predict weather.
• In weather forecasting there are 2 main types of data
  assimilation: 3 dimensional (3DDA) and 4 dimensional
  (4DDA). In 3DDA only those observations available at the
  time of analysis are used. In 4DDA the past observations
  are included (thus, time dimension added). The analysis
  and forecasts are best thought of as probability
  How Current State Gets Projected Into
                Future ?
          Numerical Weather Predictions

Numerical weather prediction uses current
weather conditions as input into (Mathematical
equations) mathematical models of the
atmosphere to predict the weather. The equations
involved in these models are complex and involve
multiple atmospheric variables.This is impossible
to use without supercomputers

How Current State Gets Projected Into
              Future ?
        Numerical Weather Predictions

  Numerical model calculations on 3-dimensional grids
 Apply weather forecast information
        (“User applications”)
• Accuweather Mobile Software

 Apply weather forecast information
        (“User applications”)
• Weather widgets for Android phone

 Apply weather forecast information
        (“User applications”)
• Weather Center for Windows XP/Vista/7

 Apply weather forecast information
        (“User applications”)
• Weather Forecast from webpage   24/29
 Limits In Weather Forecasting
• Initial state is imperfect
  –Weather forecasts lose skill because of the growth of errors in the
   initial conditions (initial uncertainties) and because numerical
   models describe the laws of physics only approximately (model
   uncertainties). As a further complication, predictability
   (i.e. error growth) is flow dependent.

                                         Initial state


                                      Less predictable

The Lorenz 3D chaos model illustrates how predictability depends on the initial conditions   25/29
Limits In Weather Forecasting

Limits In Weather Forecasting

• Numerical model is imperfect
 – Limited resolution
    ~Using a finer resolution for the model grid will more
    accurately reflect the actual atmosphere, and the
    prediction will more accurately forecast the weather. But the
    finer the resolution, the more data that has to be gathered and
    numbers that have to be crunched.
    ~So, in practice, models that cover large areas (e.g whole
    Northern hemisphere) have rough resolution than those that
    cover smaller areas (e.g the USA) and so are not going to be as
    accurate in the small scale.

• Book : “The Beginning Forecaster-The Forecasting Process Through
  Data Analysis” by HANS LEVENBACH, JAMES P. C
• products/systems/synop.htm


              -THE END-

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