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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 May, 2002 Numerical Weather Prediction 1 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 May, 2002 Numerical Weather Prediction 2 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 May, 2002 Numerical Weather Prediction 3 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 May, 2002 Numerical Weather Prediction 4 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 May, 2002 Numerical Weather Prediction 5 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 May, 2002 Numerical Weather Prediction 6 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) May, 2002 Numerical Weather Prediction 7 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?MODEL=ngm May, 2002 Numerical Weather Prediction 8 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?MODEL=eta May, 2002 Numerical Weather Prediction 9 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 May, 2002 Numerical Weather Prediction 10 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 May, 2002 Numerical Weather Prediction 11 Aviation Model • • • • • Generates aviationfocused data 42 vertical layers, 100 km horizontal resolution Advantage: mediumrange forecasting (up to 72 hours) One of the oldest operational models Data results available mostly in MOS (model output statistics) format May, 2002 http://weather.unisys.com/aviation/index.html Numerical Weather Prediction 12 MM5 • • Fifth generation mesoscale NWP Study types – hurricanes – cyclones – monsoons – fronts (formation, interactions) – land-sea breeze meteorology – urban heat islands – mountain-valley circulations May, 2002 http://rain.mmm.ucar.edu/mm5/ Numerical Weather Prediction 13 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 May, 2002 Numerical Weather Prediction 14 Sample Prediction Solution May, 2002 Numerical Weather Prediction 15 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 May, 2002 Numerical Weather Prediction 16 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 May, 2002 http://www.shodor.org/bob2/wx/weather predict.html Numerical Weather Prediction 17 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 May, 2002 http://www.emc.ncep.noaa.gov/mmb/meteograms/ Numerical Weather Prediction 18 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 May, 2002 Numerical Weather Prediction 19 Questions? • Chat Sessions – Monday, May 13 3:304:30 PM and 6:00-7:00 PM – Wednesday, May 15 3:304:30 PM – Monday, May 20 6:007:00 PM – Thursday, May 23 3:304:30 PM and 6:00-7:00 PM May, 2002 Numerical Weather Prediction 20