Weather Forecasts: From Tragedy to Triumph Cliff Mass University of Washington
2012: Hurricane Sandy 125 dead, 60+ billion dollars damage
Well predicted over a week ahead of time ECMWF 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 National Weather Service Forecast Error Better Year
Skill Improvements (ECMWF) Major improvements, mainly due to satellite data and improved models
The Revolution in Weather Prediction Technology
The Key Technology of Modern Weather Forecasting is Numerical Weather Prediction
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.
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 Weather Service Weather Prediction Computer
NGM, 80 km, 1995
2007-2008 4-km MM5 Real-time
1.33 km resolution available on the UW web site
But just as important 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 Polar Orbiter Weather Satellite
Satellite Sensors Provide Thousands of High Quality Vertical Soundings Daily over the Pacific
Cosmic GPS Satellites Provide More Soundings!
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 our model physics (e.g., clouds and precipitation processes) 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 detail the weather profession can provide has greatly increased. High resolution forecasting, NWS forecasts on a 2.5 km grid, radar data, satellite imagery, huge numbers of surface stations, and now probabilistic prediction!
Example: The Pacific Northwest Based on 72 different networks 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 Provide Typical TV weathercasters have only 2.5 minutes!
Many of us worried about this problem in the 90’s but now the solution is literally at hand
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.
There are now thousands of weather apps for smartphones…and the best are yet to come!
Some Tragedies Continue Little Improvement in Forecasting the Intensity of Hurricanes
Tragedy: The U.S. is Now in Second or Third Place in Global Weather Prediction
The End