May, 2002 Numerical Weather Prediction

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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

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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?MODEL=ngm

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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?MODEL=eta

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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 3:30-4:30 PM and 6:00-7:00 PM

– Wednesday, May 15 3:30-4:30 PM

– Monday, May 20 6:00-7:00 PM

– Thursday, May 23 3:30-4:30 PM and 6:00-7:00 PM