Robert R. Gotwals, Jr. (

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Numerical Weather Prediction

• Robert R. Gotwals, Jr. (Bob2)
• Computational Science Educator
• The Shodor Education Foundation, Inc.
• http//www.shodor.org
• http//www.shodor.org/talks/nwp

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Session Goals

• Describe application, algorithm, and architecture
• Describe and demonstrate the various NWP programs
  and codes
• Describe appropriate and authentic classroom
  activities using online NWP tools

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Application - First Principles

• Definition
• The use of computer models to predict the future
  state of the atmosphere given observations and
  equations that describe relevant physical
  processes
• Some givens
• Weather prediction is really hard
• Synoptic scale calculations, but local influences
• Equations are nonlinear

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Application - Results

• Example plots
• Temperature
• Dewpoint
• Mean sea level pressures (MSLP)
• Winds, surface and aloft
• Cloud cover
• Precipitation and types
• Severe weather indices
• CAPE
• Helicity

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Algorithm - NWP Desks

• Desk seat 1 calculates east-west component of
  the wind
• Desk seat 2 calculates north-south component of
  the wind
• Desk seat 3 keeps track of the air entering or
  leaving the box. If more is coming in than going
  out, decides how much air rises or sinks
• Desk seat 4 calculates the effects of adding or
  taking away heat
• Desk seat 5 keeps track of water in all forms
  and how much is changing to or from vapor,
  liquid, or ice
• Desk seat 6 calculates the air temperature,
  pressure, and density

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Architecture - Platforms

• NWP requires significant computing power
• True supercomputing required
• Gigaflops - billions of calculations (floating
  point operations) per second
• Teraflop - trillions of calculations per second
• Data storage
• NCAR - late 2000, 200 terabytes of data stored
• NCAR machine
• 11th most powerful supercomputing in the world
• IBM SP Power 3
• 1260 CPUs (processors)
• Peak capabilities 1890 Gigaflops

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Architecture - Codes

• General categories
• By resolution
• By scale
• Global (northern hemisphere)
• National
• relocatable
• By outlook (time-based)
• Well-known codes
• Nested Grid Model (NGM)
• ETA
• Aviation Model (AVN)
• Rapid Update Cycle (RUC)
• Medium Range Forecast (MRF)
• Mesoscale Model 5 (MM5)

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Nested Grid Model (NGM)

• National model
• Short-range model (48 hours), every 6 hour
  forecasts
• Forecast output
• Temperature
• Precipitation
• Upper and lower trough positioning
• Surface highs and lows
• Grid size 80 km
• Operational status being phased out

http//weather.uwyo.edu/models/fcst/index.html?MOD
ELngm
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ETA

• Name comes from eta coordinate system
• Short-range model
• Four runs daily 0000Z, 0600Z, 1200Z, 1800Z
• 32 km horizontal domain, with 45 vertical layers
• Significantly outperforms other models in
  precipitation predictions

http//weather.uwyo.edu/models/fcst/index.html?MOD
ELeta
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Rapid Update Cycle

• Regional model
• Short-term forecasts
• Up to 12 hours
• Focuses on mesoscale weather features
• 25 vertical layers, 40 km horizontal resolution
• New experimental version MAPS
• RUC/MAPS generate significant amount of data

http//weather.unisys.com/ruc/index.html
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Medium Range Forecast (MRF) Model

• Global model
• Medium to long-range predictions 60 to 240
  hours
• Resolution 150 km
• Other global models
• UKMET
• ECMWF
• Global Ocean Model

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Aviation Model

• Generates aviation-focused data
• 42 vertical layers, 100 km horizontal resolution
• Advantage medium-range forecasting (up to 72
  hours)
• One of the oldest operational models
• Data results available mostly in MOS (model
  output statistics) format

http//weather.unisys.com/aviation/index.html
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MM5

• Fifth generation mesoscale NWP
• Study types
• hurricanes
• cyclones
• monsoons
• fronts (formation, interactions)
• land-sea breeze meteorology
• urban heat islands
• mountain-valley circulations

http//rain.mmm.ucar.edu/mm5/
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Sample Prediction

• Question assuming precipitation, what will it
  be?
• Tools
• Atmospheric sounding (weather balloon data)
• Shows temperature and dewpoint temperature from
  surface to upper atmosphere
• Flowchart precipitation type decision tree
• Analysis/solution shown on next slide

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Sample Prediction - Solution
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Classroom Integration - Forecasting Rules of thumb

• Will it be cloudy or clear?
• On the 700-mb forecast chart, the 70 relative
  humidity line usual encloses areas that are
  likely to have clouds
• Will it rain?
• On the 700-mb forecast chart, the 90 relative
  humidities line often encloses areas where
  precipitation is likely.
• Will it rain or snow?
• On the 850-mb forecast chart, snow is likely
  north of the -5 C (23 F) isotherm, rain to the
  south

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Classroom Integration - Weather observations

• Correlating low-tech weather observations
• Use instant weather prediction chart
• Shows various weather 24 hours out based on
  easily observable meteorological phenomenon
• Can correlate this with model data

http//www.shodor.org/bob2/wx/weather predict.html
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Classroom Integration

• Good starting place meteograms
• Relatively easy to interpret
• Contain a lot of data
• Typically project out 24 to 72 hours
• Relatively good resolution (normally 22 km)
• Available from a variety of models

http//www.emc.ncep.noaa.gov/mmb/meteograms/
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Classroom Integration

• Harder atmospheric soundings graphs
• Substantial amounts of information
• Graphical and text-based information
• Graphical temperature, dewpoint temperatures,
  wind speeds and directions
• Text key meteorological indices

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Questions?

• Chat Sessions
• Monday, May 13 330-430 PM and 600-700 PM
• Wednesday, May 15 330-430 PM
• Monday, May 20 600-700 PM
• Thursday, May 23 330-430 PM and 600-700 PM