Numerical Models

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Lecture 10 (11/11)

• Numerical Models

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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

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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

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More problems

• If initial state (called the initialization or
  analysis) is not accurate, then computers
  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

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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

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Key Things to Remember

• When looking at model data, always
• Look at the date and time - make sure its 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!

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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

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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.

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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

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MRF model

• Produces medium range forecasts (like the name
  suggests)
• Version of AVN that is run out to 14 days
• Dont bet on the 7-14 day forecasts being
  accurate
• Good for a longer look at weather

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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.)

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Comparing (ETA vs MRF)
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Comparing (AVN vs NGM)
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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

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MOS (AVN example)
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Web pages for Model Output

• Remember you can always go to http//weather.ou.ed
  u/wx and click on links
• Unisys http//weather.unisys.com
• Texas AM (click on model output)
  http//www.met.tamu.edu/weather.shtml
• NCAR http//www.rap.ucar.edu/weather

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For Next time

• Read Ch 7 (Snow and Ice) about riveting topics
  like Snow and Ice )
• Next homework on web
• For the homework, youll 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)