The Technology and Future of Weather Forecasting Cliff Mass University of Washington

1. The Technology and Future of Weather ForecastingCliff MassUniversity of Washington

2. 2012: Hurricane Sandy 125 dead, 60+ billion dollars damage in an area with a population of tens of millions.

3. Well predicted, more than a week ahead ECMWF 6-day Forecast of Sea Level Pressure

4. 1938 Hurricane: Similar in Strength to Sandy Nearly a thousand died

5. Not forecast the day before

6. 1962 Columbus Day Storm

7. Not forecast the day before either Seattle Times

8. Jan 1993: Inauguration Day Storm: Near Perfect Forecast

9. Something Has ChangedBefore 1990 the National Weather Service got virtually every major storm wrong, even the day before.After 1990, they gave good warnings for nearly all.

10. Forecast Skill Improvement National Weather Service Forecast Error Better Year

11. Skill Improvements (ECMWF) Major improvements, mainly due to satellite data and improved models

13. Weatherman Jokes Are No Longer Appropriate

14. The Key Technology of Modern Weather Forecasting is Numerical Weather Prediction

15. 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

16. 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.

17. Observation Collection Needed to Create the Initialization

18. Numerical Weather Prediction One of the equations used to predict the weather is Newton’s Second Law: F = ma Force = 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)

19. This equation is a time machine!

20. F = ma • 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.

21. The “Primitive” Equations

22. 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 Weather Service Weather Prediction Computer

23. NGM, 80 km,1995

24. 1995

25. 2007-2008 4-km UW MM5 System

26. 1.33 km resolution available on the UW web site

27. 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

28. Example: The Pacific Data Void No Longer Exists

30. Cloud Track Winds

31. Better than Star Trek!

33. NOAA Polar Orbiter Weather Satellite

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

35. 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

36. Observed 180 hr (7.5 days)

37. 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.

38. Increasing Resolution and Better Models Will Not Be EnoughThe Next Major Revolution in Numerical Weather Prediction Will Come Elsewhere

39. The Transition from Deterministic to Probabilistic Prediction

40. 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….

41. 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.

42. This is Ridiculous!

43. 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

44. 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.

46. Ensemble Prediction • Can use ensembles to give the probabilities that some weather feature will occur. • The 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.

47. 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.

48. The Nowcasting Revolution

49. 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

50. Huge amounts of local data has come online during the past several decades