The Technology and Future of Weather Forecasting

Cliff MassUniversity of Washington

2012: Hurricane Sandy

125 dead, 60+ billion dollars damage in an area with a population of tens of millions.

Well predicted, more than a week ahead

ECMWF 6-day Forecast of Sea Level Pressure

1938 Hurricane: Similar in Strength to Sandy

Nearly a thousand died

Not forecast the day before

1962 Columbus Day Storm

Not forecast the day before either

Seattle Times

Jan 1993: Inauguration Day Storm: Near Perfect Forecast

Something Has Changed

Before 1990 the National Weather Service got virtually every major storm wrong, even the

day before.

After 1990, they gave good warnings for nearly all.

Forecast Skill Improvement

ForecastError

Year

Better

National Weather Service

Skill Improvements (ECMWF)

Major improvements, mainly due to satellite data and improved models

Weatherman Jokes Are No Longer Appropriate

The Key Technology of Modern Weather Forecasting is

Numerical Weather Prediction

The First Numerical Weather Prediction

• The first successful numerical prediction of weather was made in April 1950, using the ENIAC computer at Maryland's Aberdeen Proving Ground

Numerical Weather Prediction

• The basic idea is that if you can determine the current state of the atmosphere (known as the initialization) , you can predict the future using the equations that describe the physics of the atmosphere.

• These equations can be solved on a three-dimensional grid.

Observation Collection Needed to Create the Initialization

Numerical Weather Prediction

One of the equations used to predict the weather is Newton’s Second Law:

F = maForce = mass x acceleration

Mass is the amount of matter

Acceleration is how velocity changes with time

Force is a push or pull on some object (e.g., gravitational force, pressure forces, friction)

This equation is a time machine!

•The initialization gives the distribution of mass (how much air there is and where) and allows us to calculate the various forces.

•Then… we can solve for the acceleration using F=ma

•With the acceleration we can calculate the velocities in the future.

•Similar idea with temperature and humidity but with different equations.

F = ma

The “Primitive” Equations

Numerical Weather Prediction• Numerical weather prediction is limited by the

available computer resources.

• As computer speed increases, the number of grid points can be increased.

• More (and thus) closer grid points means we can simulate (forecast) smaller scale features.

National WeatherService WeatherPrediction Computer

NGM, 80 km,1995

1995

2007-2008

4-km UWMM5 System

1.33 km resolution available on the UW web site

But just as important as the computer revolution has been the

weather data revolution, with satellites giving us three

dimension data over the entire planet

Example: The Pacific Data Void No Longer Exists

Cloud Track Winds

Better than Star Trek!

NOAA PolarOrbiter WeatherSatellite

Satellite Sensors Provide Thousands of High Quality Vertical Soundings Daily over the Pacific

Cosmic GPS Satellites Provide More Soundings!

Impacts

• The addition of massive amounts of new observations is causing a steady improvement in weather prediction

• We are now starting to see frequent examples of forecast skill past one week:

• Hurricane Sandy is only one example

Observed 180 hr (7.5 days)

Forecast Skill Will Continue to Extend Further in Time…with

limits (about 2 weeks)

• More satellite assets will provide a far better description of the atmosphere.

• Better models and higher resolution

• Better data assimilation: how we use the observations to produce an initialization for our models.

Increasing Resolution and Better Models Will Not Be Enough

The Next Major Revolution in Numerical Weather Prediction

Will Come Elsewhere

The Transition from Deterministic to Probabilistic

Prediction

A Fundamental Problem• The way we have been forecasting

has been essentially flawed.

• The atmosphere is a chaotic system, in which small differences in the initialization…well within observational error… can have large impacts on the forecasts, particularly for longer forecasts.

• Not unlike a pinball game….

A Fundamental Problem

• Similarly, uncertainty in processes, like the development of clouds and precipitation, also produces uncertainty in forecasts.

• Thus, all forecasts have some uncertainty.

• The uncertainty generally increases in time.

This is Ridiculous!

Forecast Probabilistically

• We should be using probabilities for all our forecasts or at least providing the range of possibilities.

• There is an approach to handling this issue that is being explored by the forecasting community…ensemble forecasts

Ensemble Prediction

• Instead of making one forecast…make many…each with a slightly different initialization or different model physics.

• Possible to do this now with the vastly greater computation resources that are available.

Ensemble Prediction

•Can use ensembles to give the probabilities that some weather feature will occur.

• Ensemble mean is more accurate than any individual member.

•Can also predict forecast skill!•When forecasts are similar, forecast skill is generally higher.•When forecasts differ greatly, forecast skill is less.

Prediction!

• The meteorological profession is rapidly gaining the ability to produce high-resolution probabilistic weather forecasts AND analyses.

• Probabilistic forecasts and analyses will be available for a wide range of weather parameters.

The Nowcasting Revolution

AMS Nowcasting Definition

A description of current weather and a short-term forecast varying from minutes to a few hours; typically shorter than most operational short-range forecasts.

American Meteorological Society’s Glossary of Weather and Climate

During the past decade or so the geographical and temporal specificity of

the information that the weather profession can provide has greatly

increased.

Pacific Northwest Surface Observations

3000-4000 observations per hour over WA and OR

Traditional Approaches of Weather Information

Dissemination Are Incapable of Delivering the Specificity and

Detail Meteorologists Can Now Provide

Typical TV weathercasters have only 2.5 minutes!

There has never been such a large difference between what meteorologists know about current weather and what we are communicating to the public.

An Irony

A Worry

The Solution? Smartphones are Ideal for Weather Data Delivery.

• Lots of bandwidth• They know where they are, so forecast

information can be tailored to the user• Substantial computational capacity.

Smartphones Offer a Powerful, Portable Platform for Viewing Weather Information, Forecasts, and Warnings

There are now thousands of weather apps for

smartphones…and the best are yet to come!

WeatherProtector

WEATHERPROTECTOR

Tells you whether heavy precipitation, winds, or other weather issue are approaching your position.

BikeWeatherGuard

Bike WeatherGuard

•Using a map interface, describe your planned route and when you want to travel.•Tells you whether you should delay your trip, or perhaps leave a few minutes early, to stay dry.

The Weather Adaptive Society

• Advances in computation, control, and communication allows society to react quickly and effectively to weather information.

• At the same time, weather forecasts will rapidly improve.

• Together they allow effective real-time weather adaptation.

Traffic Can Be Slowed During Dangerous Weather

Can use flow control to limit the number of cars entering the roadways near heavy rain.

Power Generation• Coordination of power generation by

weather-sensitive renewables and reserve power sources (e.g., hydro, gas turbines).

Weather Forecasting is Only One Part of Atmospheric Sciences

• Climate research and prediction

• Severe weather research and prediction (hurricanes, tornadoes, severe thunderstorms, windstorms, snowstorms)

• Atmospheric pollution and chemistry

• Mountain meteorology

• And many more…

The End