Lecture 10 (11/11)

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 • Unisys: http://weather.unisys.com • Texas A&M: (click on model output) http://www.met.tamu.edu/weather.shtml • NCAR: http://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/Metr151/151home.html (see hmwk for more details)