1. Lecture 10 (11/11) Numerical Models

2. Numerical Weather Prediction Numerical Weather Prediction (NWP) uses the power of computers and equations to make forecasts Run on supercomputers Provide predictions for many atmospheric variables like temperature, pressure, wind, and precipitation

3. More on NWP NWP is not perfect: Bad Data (sensor is messed up) Data not representative of surroundings Gaps in available data Equations in model not perfect Some assumptions made Chaos theory - small scale stuff can have a significant effect on weather

4. More problems If initial state (called the initialization or analysis) is not accurate, then computer’s prediction of how initial state evolves could be especially bad Despite these problems, models are often quite accurate Important to know strengths and weaknesses of models and how they work

5. Good Forecasts A good forecast can often be made with a meteorologist interpreting model data and adding his/her own expertise Model or forecaster alone = problems Model + forecaster = usually works well As research and technology advances, weather models are updated (several times a year) to try to make more accurate forecasts

6. Key Things to Remember When looking at model data, always: –Look at the date and time - make sure it’s for the period you want to look at –Look at the initialization - does it closely match the current conditions? If not, the forecasts are probably bad too –Does it make sense? - A blizzard in Norman in August probably would not happen!

7. The Models The major models: *Eta model (ETA) *Aviation model (AVN) Nested Grid Model (NGM) *Medium Range Forecast Model (MRF) *Rapid Update Cycle (RUC) European Center for Medium Range Weather Forecasting (ECMWF) *=most important

8. ETA model Most widely used model in operational meteorology in U.S. Better than other models for convective precipitation (like thunderstorms) Gives 3 day forecasts The 0 & 12Z cycles run out to 60 hours, the 06 & 18Z cycles run to 48 hours. Run twice a day at 0z and 12z with output for every 12 hours out to 60 hours.

9. Aviation Model Covers entire Northern Hemisphere Useful for looking upstream and around the world Less detailed than ETA over U.S. but also a pretty good model Forecasts out to 84 hrs at 6Z & 18Z and all the way out to 126 hours at 0Z & 12Z

10. MRF model Produces medium range forecasts (like the name suggests) Version of AVN that is run out to 14 days Don’t bet on the 7-14 day forecasts being accurate Good for a longer look at weather

11. RUC model RUC = Rapid Update Cycle Run every 3 hours for forecasts out to 12 hours Helps for forecasts for the next few hours Designed to incorporate the latest weather parameters every 3 hours (temps, dewpoints, winds, pressures, etc.)

12. Comparing (ETA vs MRF)

13. Comparing (AVN vs NGM)

14. Model Output Statistics Called MOS for short (gotta love acronyms!) Found on Rossby using the Weather command Presents model forecasts in a text format Often can give more background forecast information

15. MOS (AVN example)

16. Web pages for Model Output Remember you can always go to http://weather.ou.edu/wx and click on links http://weather.ou.edu/wx Unisys: http://weather.unisys.comhttp://weather.unisys.com Texas A&M: (click on model output) http://www.met.tamu.edu/weather.shtml http://www.met.tamu.edu/weather.shtml NCAR: http://www.rap.ucar.edu/weatherhttp://www.rap.ucar.edu/weather

17. For Next time: Read Ch 7 (Snow and Ice) about riveting topics like: Snow and Ice ;) Next homework on web For the homework, you’ll need to read part 1 of tutorial #20 from the following website: http://www.met.tamu.edu/class/Metr151/15 1home.html (see hmwk for more details) http://www.met.tamu.edu/class/Metr151/15 1home.html