Weather Forecasting

Yean Lee Low 6th December 2010

OVERVIEW

• Introduction• Objective of Weather Forecasting• What Types of Weather Forecasting

Exists? • The Makings Of A Weather Forecast• Limits In Weather Forecasting• Sources

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Introduction

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)

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Introduction

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)

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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.

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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 crops.

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What Types of Weather Forecasting Exists?

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)

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The Makings Of A Weather Forecast (1/2)

WHAT WE NEED FOR PREPARING A USEFUL FORECAST?

•Assess current weather situation (“Initial condition”) - Before we can look into future, understand what is happening now

•Digest observational information (“Data assimilation”) - Bring observed data into “standard” format

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The Makings Of A Weather Forecast (2/2)

• 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

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Observing The Current State –Surface-Based Systems

Land surface - SYNOP stationSYNOP (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.

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Observing The Current State –Surface-Based Systems

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http://www.mesotech.com/ products/systems/synop.htm

SYNOP station

General structure of a SYNOP message

Observing The Current State –Surface-Based Systems

12/29http://rxcontrol.free.fr/SynopCtl/

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.

Observing The Current State –Surface-Based Systems

Ocean – buoyWeather 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.

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Observing The Current State –Surface-Based Systems

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Weather buoy

http://en.wikipedia.org/wiki/Buoy

Example of Buoy data.

meted.ucar.edu

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 satellites.

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

POINTS”

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16/29http://www.tropicalweather.net/hurricane_and_tropical_weather_message_board/viewtopic.php?f=57&t=957

• Satellite imagery

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

POINTS”

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

POINTS”

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• 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

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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 distributions.

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

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How Current State Gets Projected Into Future ?

Numerical Weather Predictions

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Numerical model calculations on 3-dimensional grids

Apply weather forecast information (“User

applications”)• Accuweather Mobile Software

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Apply weather forecast information (“User

applications”)• Weather widgets for Android

phone

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Apply weather forecast information (“User

applications”)• Weather Center for Windows

XP/Vista/7

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Apply weather forecast information (“User

applications”)• Weather Forecast from webpage

24/29http://new.meteo.pl/index_en.php

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.

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More predictable

Less predictable

The Lorenz 3D chaos model illustrates how predictability depends on the initial conditions

Initial state

Limits In Weather Forecasting

26/29http://en.wikipedia.org/wiki/Butterfly_effect

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.

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Sources

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

• http://en.wikipedia.org/wiki/Numerical_weather_prediction• http://wwwt.emc.ncep.noaa.gov/gmb/ens/index.html• http://www.windfinder.com/forecasts/forecast_models.htm• http://www.mesotech.com/ products/systems/synop.htm• http://rxcontrol.free.fr/SynopCtl• meted.ucar.edu• http://www.tropicalweather.net/

hurricane_and_tropical_weather_message_board/viewtopic.php?f=57&t=957

• http://new.meteo.pl/index_en.php• http://www.scn.org/~bm733/infaq.html

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THANK YOU

-THE END-

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