WEATHER FORECASTING

A Scientific Look into the Future.Prepared by: Margaret Milligan, July 5, 2005

HISTORY OF FORECASTING

• Weather forecasting began with early civilizations using reoccurring astronomical and meteorological events to monitor seasonal changes in the weather.– By 300 BC the Chinese developed a calendar which

divided the year into 24 festivals, with each festival celebrating a different type of weather.

– Aristotle's ideas in the text Meteorologica stuck for almost 2000 years – even though many claims were erroneous.

– The Renaissance brought about the first types of instruments used to measure factors affecting weather.

– The 19th Century saw a global compilation of weather data and the beginning of more accurate forecasting.

HISTORY OF FORECASTINGIN THE UNITED STATES

• National Weather Organization set up in 1870 under the Secretary of War to forecast storms in the Great Lakes and Atlantic Seaboard. Done in order to cut down on shipping loses.

• United States Army Signal Service continued to grow and spread across the country.

• Interested in more history and application of weather forecasting?Check out: Issac’s Storm byErik Larson“A Man, a Time, and the Deadliest Hurricane in History”

FORECASTING METHODS

• Persistance Method: Hot today, Hot tomorrow.- Basically used for short term forecasting. - Works well in areas where there are little changes day to day. ie: California- Can be accurate in long term forecasting. A hot and dry month will most likely be followed by another hot and dry month.

• Trends Method: Math in action!- Uses math to make predictions.- A storm is 1000 miles away moving at 250 mph. The trends method would predict stormy weather in 4 days.- Works best with systems moving with a consistent velocity.

FORECASTING METHODS

• Climatology- Use years of data to predict what type of weather will occur on certain days.- Works well in areas of predictable weather patterns. Not accurate in day to day weather.

• Analog Method- Looking at today’s weather and comparing it to weather in the past.- Today is warm, but a cold front is approaching. The previous cold front produced stormy weather, so storms are forecasted again.- Hard to be accurate because of natural variations in weather systems.

• Numerical Weather Prediction- Use of computer programs to make a forecast.- Programs provide predictions of temperature, pressure, wind, and rainfall. These features used to predict the weather of the day.- Flaws include incomplete data or incorrect equations in program, which lead to flawed forecasts. BEST OF THE FIVE TYPES!

SURFACE FEATURES

• There are key surface features which need to be observed in order to make an accurate forecast.– Anticyclones (high pressure)– Cyclones (low pressure)– Cold, Warm, Stationary, and Occluded Fronts– Dry Lines– Clouds– Temperature– Moisture/Precipitation

A dry line formingwest of Texas. Dry lines are extremely rareeast of the Mississippi.

SURFACE FEATURES

• ANTICYCLONES (HIGH)– Brings clam, fair weather– Air moves away from

center of high, sinking air replaces it

– Temperature depends on location relative to high

• Northerly winds: cooler• Southerly winds: warmer

• CYCLONES (LOWS)– Brings stormy, unsettled

weather– Air moves towards center

of low, causes air to rise – Rising motion may result

in clouds and precipitation.– Lows are associated with

fronts

SURFACE FEATURES

• Warm FrontsWarm air replacing cool airLight intensity precipitation

seen in front of and behind the front in large area

• Stationary FrontsNon moving front.Separate warm and cool air

masses.Can be the beginning of cyclone

(see Norwegian Cyclone Model)

• Occluded FrontsOccur when a cold front

“catches” a warm frontCuts off supply of warm, moist airDeath of cyclone

• Cold FrontsCold air replacing

warm air.Warm air lifted and cooled,

moisture condenses to form clouds and precipitation.

NORWEGIAN CYCLONE MODEL

1. Stationary front forms separating warm and cool air masses

4. Mature low pressure system. Occluded front, system dissipates

2. A wave develops on the front and precipitation begins to form

3. The wave intensifies and cold and warm fronts organize

SURFACE FEATURES

• Dry LinesBoundary between a moist air

mass and a dry air massDry air can cause moist air to rise

and clouds and precipitation develop similar to cold front

• CloudsDay Clear: warmer temps

predictedDay Cloud: cooler temps predictedNight Clear: cooler tempsNight Cloudy: warmer temps

• TemperatureWhen forecasting, look at

stations upsteamWarm air advection: warmer

tempsCold air advection: cooler temps

• MoistureEven if lifting is occurring,

precipitation will not occur if dew points are too low.

REMOTE SENSING

• The science of obtaining information about a subject without being in contact with the subject.

• Weather forecasting uses devises sensitive to electromagnetic energy such as – Light: (satellite)– Heat: (infrared scanning on satellites)– Radio waves: Doppler Radar

REMOTE SENSING

• Doppler Radar– Radio antenna turns and sends out radio waves with short listening periods between pulses.– The amount of time needed for wave to return tells us

distance to object.– Returns in clear air can tell us a lot also. Radar waves hitting bugs can inform us of air motion and wind direction.- Most often used to ID precipitation. As seen in the image to the left, areas of

greater precipitation are shown in reds and pinks, while blues blue and greens represent light precipitation. High reflectivity (grey) represents hail.

REMOTE SENSING

• Doppler Radar– Most used to determine wind direction and

possible tornados within severe storms.– Air moving towards the radar are shaded green

while air moving away from the radar are shaded red.

– Tornados form in areas where the wind is blowing in opposite directions over a small distance. A tornado developed six minutes after the radar image to the right was taken. It formedin the area near the bright green patch.

REMOTE SENSING

REFLECTIVE IMAGE STORM RELATIVE VELOCITY

REMOTE SENSING

• Satellites– Polar Orbiting Satellite (POES)

• Close to the earth, detailed images, views of polar regions• Can’t see whole surface, orbit changes due to Earth’s

rotation, 6 6 to 7 images a day

– Geostationary Orbiting Satellite (GOES)• Same spot in sky relative to earth, views entire surface,

fast imaging, view motion on Earth, can collect data from stations.

• Far from earth, loss of detail, limited view of polar region.

REMOTE SENSING

• Visible ImageryAn image of the Earth in visible lightDetects reflected sunlight, thick

clouds appear brighter.Excellent for detecting developing

thunderstorms

• Infrared ImageryAn image using Infrared light.Senses radiant heat given off by

clouds.Used for detecting clouds and

thunderstorms when sunlight is not present.

• Water Vapor ImageryDetects water vapor in addition to

clouds.Only “sees” top third of Troposphere

Moist areas are white, dry areas are black

• Derived Satellite ImagesExample: Lifted Index

Shows instability present in the atmosphere.Can predict where storms may form.

Satellites: Types of Images

REMOTE SENSING

• Visible Imagery • Infrared Imagery

• Water Vapor Imagery • Derived Satellite Images

Satellites: Types of Images, Tropical Storm Isidore

Light blue: Very StableGreen: StableYellow: Slightly UnstableOrange: UnstableRed: Very UnstablePink: Extremely Unstable*Thunderstorms likely orange and above, Severe if lifting mechanism present.

REMOTE SENSING

• Automated Surface Observing Systems (ASOS)– Works non-stop, 24 hours a day, updating every minute– Reports the following information

• Sky conditions such as cloud height and cloud amount up to 12,000 feet,

• Surface visibility up to at least 10 statute miles, • Basic present weather information such as the type and

intensity for rain, snow, and freezing rain, • Obstructions to vision like fog, haze, and/or dust, • Sea-level pressure and altimeter settings, • Air and dew point temperatures, • Wind direction, speed and character (gusts, squalls), • Precipitation accumulation• Selected significant remarks including- variable cloud

height, variable visibility, precipitation beginning/ending times, rapid pressure changes, pressure change tendency, wind shift, peak wind.

REMOTE SENSING

• Radiosondes– A small instrument package attached to a balloon.– The balloon lifts the package as measurements

are taken.- Information is sent back to weather station and

data is recorded.- The data is used for

• Input for computer-based weather prediction models, • Local severe storm, aviation, and marine forecasts• Weather and climate change research• Input for air pollution research• Ground truth for satellite data.

FORECASTING IN ACTION

• IBM’s Deep Thunder is a computer program that can make short term weather predictions based on data from weather stations.

• Deep thunder created the following 3D images of forecasted thunderstorms at 8pm on May 31, 2005 in New York.

Deep Thunder Animation

FORECASTING IN ACTION

• Forecasts predicted a warm and humid day. Deep Thunder predicted storms late in the day as a cold front approached.

• The following animation shows a shift in winds, lifting, and formation of thunderstorms.

• Deep Thunder’s predictions were only off by 30 minutes. All other predictions, including area of rain, rainfall totals, and wind directions, were accurate.

Rain and wind animation

THE FUTURE OF FORECASTING

• Scientists are striving to increase warning time for severe weather such as tornados and flash floods with the help of forecasting technology. More accurate forecasting can continue to help forecast the path of tropical cyclones.

• In its simplest form, weather forecasting is used for day to day living.

• Long term forecasts can predict droughts, rainy periods, frost, and other important weather affecting agriculture.

• Historical forecasts and data can be used to determine changes in climate and its effect on an ecosystem.

WEATHER FORECASTING

FORECASTING WEBSITES• The Weather Channel• Weather Underground• WeatherBug• National Weather Service

LESSON PLANS•Forecasting – Grades 2-6•Weather Forecasting – Grades 6-8•Weather Patterns – Grade 4-8•Kids as Global Scientists – Grade 6-8•Weather Forecasting Research – Grade 6-8

RESOURCES

• INTERNET RESOURCESUniversity of Illinois Online Weather GuidesUSA Today Weather ForecastingJetStream – An Online Weather SchoolThe Weather ChannelNational Weather ServiceNational Geographic: Fire and Rain, Forecasting the Chaos of

WeatherWeather Forecasting Through the Ages (NASA)Economic History of Weather Forecasting

• TEXT RESOURCESNational Geographic: June 2005The Atmosphere, 7th Edition (Lutgens and Tarbuck)Isaac’s Storm (Larson)The Usborne Internet-linked Science EncyclopediaOnline Weather Studies, 2nd Edition (Moran)