Lecture 10 (11/11)

Numerical Models

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

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

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

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

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!

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

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.

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

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

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.)

Comparing (ETA vs MRF)

Comparing (AVN vs NGM)

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

MOS (AVN example)

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

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)