1. Technology on the Cutting Edge of Weather Research and Forecasting
Dr. Dave Dempsey
Professor of Meteorology
Department of Geosciences, SFSU

2. Technology on the Cutting Edge of Weather Research and Forecasting
How modern weather forecasting works
How to make better weather forecasts

3. Pre-modern Weather Forecasting A Rule of Thumb: Red sky at morning,
sailors take warning;
red sky at night,
sailors’ delight

4. How Modern Weather Forecasting Works
The atmosphere is mostly a fluid
a mixture of gases (air)
tiny liquid & solid particles (clouds, aerosols)
Air obeys basic physical laws:
Conservation of momentum
Conservation of energy
Conservation of mass
Ideal gas law

5. How Modern Weather Forecasting Works (cont’d)
Physical laws expressed mathematically:
Nonlinear, coupled, partial differential equations for temperature, pressure, density, wind, and moisture

6. How Modern Weather Forecasting Works (cont’d)
To solve the equations, in principle:
Measure temperature, pressure, winds, moisture (weather observations) everywhere in the atmosphere at once (initial conditions)
Integrate the equations from the initial time to any future time (the forecast)

7. How Modern Weather Forecasting Works (cont’d)
Small Problem #1: We can’t measure the state of the weather everywhere at once!
“Solution”:
Measure everywhere we can and interpolate (i.e., make informed guess) in between
Small Problem #2: The equations have no known exact solutions!

8. How Modern Weather Forecasting Works (cont’d)
Solution:
First, calculate solution only on a three-dimensional grid of points in space

9. How Modern Weather Forecasting Works (cont’d)
Solution (cont’d):
Second, calculate solution only at series of discrete times

10. How Modern Weather Forecasting Works (cont’d)
Solution (cont’d):
Third, approximate physical processes at grid points and interactions between neighboring grid points (finite difference approximations) The result: a numerical model
Finally, use a computer to calculate future weather at discrete points in space and time (numerical weather forecast)

11. How Modern Weather Forecasting Works (cont’d)
Small Problem #3: The basic equations are nonlinear, and small errors in initial conditions and small model errors grow over time (atmosphere is chaotic)
Consequences:
Currently can’t forecast detailed weather beyond 5-6 days
Theoreticaly impossible to forecast detailed weather beyond ~ two weeks

12. The Public Perception:

13. How Modern Weather Forecasting Works (cont’d)
Solutions:
Make better weather observations (improve initial conditions)
Make model grid points closer together (increase model resolution)
These require new/improved technology

14. How to Make Better Weather Forecasts
Improve the observed, initial conditions
More accurate measurements
Better geographic coverage
Higher Resolution Measurements
Increase model resolution

15. How to Make Better Weather Forecasts
Improve the observed, initial conditions
More accurate measurements Example: Temperature, pressure, moisture, and wind above the earth’s surface measured by radiosondes carried by balloons

16. Network of radiosonde launching stations;
radiosondes launched twice daily, all at once

17. Radiosondes Winds are estimated by tracking the balloon with radar
Can’t track through rain/snow storm
Wind speed accuracy only ±10%
Technology improvements:
Attach Global Positioning System (GPS)
Wind speed accuracy ± 0.5-5%
GPS radiosonde receiver

18. Improve the observed, initial conditions
Better geographic coverage
Few direct observations over oceans, many Third World countries, Antarctica, etc.
Technology improvements:
Better satellite remote sensing
GOES-West water vapor images

19. Improve the observed, initial conditions
Higher resolution measurements
Technology Improvements:
Small, portable Doppler radar
Can see inside severe
thunderstorms & tornados

20. How to Make Better Weather Forecasts
Increase numerical model resolution
More grid points requires more calculations; limited by size/speed of computers
Technology Improvements:
Bigger, faster computers
Supercomputers
Use many computers at once (parallel, distributed processing)
Supercomputer at the National Center for Atmospheric Research

21. Technology Solutions:
Small Problem #4: More weather observations & more detailed numerical weather forecasts generate huge amounts of data to communicate, analyze, and display
Technology Solutions:
Better, faster internet
Internet2
New analysis and display software
Integrated Data Viewer