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Chapter 9: Chapter 9: Weather Weather
ForecastingForecasting
Acquisition of weather informationAcquisition of weather information Weather forecasting toolsWeather forecasting tools Weather forecasting methodsWeather forecasting methods Weather forecasting using surface Weather forecasting using surface
chartscharts
Acquisition of Weather Acquisition of Weather InformationInformation
World Meteorological OrganizationWorld Meteorological Organization National Centers for Environmental National Centers for Environmental
PredictionPrediction Watches: Watches: favorable condition for potential hazardous favorable condition for potential hazardous
weatherweather Warnings: Warnings: hazardous weather is imminent or actually hazardous weather is imminent or actually
occurringoccurring
Advisories: Advisories: like warning but for less hazardous like warning but for less hazardous weatherweather
• The internet plays a crucial role in the global The internet plays a crucial role in the global communication of weather information.communication of weather information.
• Go to: http://www.weather.govGo to: http://www.weather.gov
Weather Forecasting Weather Forecasting ToolsTools AWIPS: AWIPS: Advanced Weather Advanced Weather
Interactive Processing SystemInteractive Processing System used by forecasters and can used by forecasters and can
process satellite, radar, surface process satellite, radar, surface observation, radiosonde data observation, radiosonde data and weather forecasting model and weather forecasting model outputoutput
meteogrammeteogram soundingsounding
Fig. 9-1, p. 238
Near Orlando, FLHail size > 3 inch100% probability
Satellites and Weather Satellites and Weather ForecastingForecasting
geostationary satellitesgeostationary satellites polar orbiting satellitespolar orbiting satellites Geostationary Operational Environmental Geostationary Operational Environmental
SatelliteSatellite infrared images: infrared images: estimate height; 3-D imageestimate height; 3-D image visible images: visible images: not useful at nightnot useful at night water vapor images: water vapor images: particularly useful for particularly useful for
clear skyclear sky http://www.goes.noaa.govhttp://www.goes.noaa.gov
Fig. 9-5, p. 240
850kmaltitude
Cannot see polarareas
Fig. 9-7, p. 241
Fig. 9-9a, p. 242
Visible Infrared Enhanced Infrared
Fig. 9-11, p. 243
The Computer and The Computer and Weather Forecasting: Weather Forecasting: Numerical Weather Numerical Weather
PredictionPrediction Analysis:Analysis: final chart using available datafinal chart using available data
numerical weather prediction (NWP)numerical weather prediction (NWP): : based on modelsbased on models
atmospheric models: atmospheric models: fluid dynamics and fluid dynamics and atmospheric physicsatmospheric physics
Progs: Progs: prosnostic chart for weather forecastprosnostic chart for weather forecast
• One of the world’s first computers was built for theOne of the world’s first computers was built for thespecific purpose of performing weather forecasts.specific purpose of performing weather forecasts.
Fig. 9-12a, p. 245
48-hr NWPforecastof 500 mbHeight
12km vs 60km
Resolution refers togrid spacing
Why NWS Forecasts go Why NWS Forecasts go Awry and Steps to Awry and Steps to
Improve ThemImprove Them grid spacinggrid spacing incomplete data incomplete data
coveragecoverage model deficiencies due model deficiencies due
to subgrid processesto subgrid processes chaoschaos ensemble forecasting: ensemble forecasting:
spaghetti plot to indicate spaghetti plot to indicate the robustness of forecast the robustness of forecast • Chaos theory tells us that weather forecasts are highly sensitiveChaos theory tells us that weather forecasts are highly sensitive
to our ability to observe the weather. Since it is impossibleto our ability to observe the weather. Since it is impossibleto observe the weather at all places at all times, weatherto observe the weather at all places at all times, weatherforecasts will never be perfect.forecasts will never be perfect.
Other Forecasting Other Forecasting MethodsMethods
persistence forecast: persistence forecast: not bad for Tucson in Junenot bad for Tucson in June trend forecast: trend forecast: assuming constant change rateassuming constant change rate analogue method: analogue method: search for similar chart in search for similar chart in
historyhistory statistical forecast: statistical forecast: routinely used; Model routinely used; Model
Output Statistics (MOS)Output Statistics (MOS) probability forecast: probability forecast: particularly for particularly for
precipitationprecipitation climatological forecast: climatological forecast: good for Tucson good for Tucson
rainfall in Junerainfall in June
Table 9-1, p. 249
What does it mean by`chance of rain is 50% for one area’?
Choose the right answera. It will rain over 50% of the areab. 50% chance that rainfall will not occur in the whole areac. 50% change that any random location in the area will receive measurable rainfall in the given period
Fig. 9-15, p. 250
Probability for a `white Christmas’ – 1 inch or more of snow
Types of ForecastsTypes of Forecasts
very short range forecast or nowcast: very short range forecast or nowcast: 0-6 0-6 hrhr
short range forecast: 6 hr – 3 daysshort range forecast: 6 hr – 3 days Mediate-range forecast: 3-8.5 daysMediate-range forecast: 3-8.5 days long range forecast: 8.5 days – 2 weekslong range forecast: 8.5 days – 2 weeks Monthly and seasonal outlooksMonthly and seasonal outlooks
• Long-range forecasts are less specific than short range Long-range forecasts are less specific than short range forecasts.forecasts.
Fig. 9-17, p. 251
Accuracy and Skill in Accuracy and Skill in ForecastingForecasting
persistencepersistence climatologyclimatology
• Both persistence and climatology are surprisinglyBoth persistence and climatology are surprisinglyaccurate forecasting methods.accurate forecasting methods.
Predicting the Weather Predicting the Weather from Local Signsfrom Local Signs
Halo: Halo: `a halo around `a halo around the moon portends the moon portends rain’ (foldlore)rain’ (foldlore)
• To see a halo: block out the To see a halo: block out the sun with your hand and sun with your hand and look at the cirrostratus clouds. look at the cirrostratus clouds. Wear polarized sunglasses if Wear polarized sunglasses if possible.possible.
Determining the Determining the Movement of Weather Movement of Weather
SystemsSystems forecasting rules of thumb: forecasting rules of thumb: surface pressure systems tend to move in the surface pressure systems tend to move in the
same direction as the 500 mb wind; the speed at same direction as the 500 mb wind; the speed at which surface systems move is about half the which surface systems move is about half the wind speed at 500 mbwind speed at 500 mb
using the surface chartusing the surface chart• Internet now provides much of the weather information
http://www.weather.govhttp://www.atmo.arizona.eduhttp://www.wrh.noaa.gov/twc
Fig. 9-20, p. 256
Current front and front 6 hr ago 500 mb height
Estimate for the next 24 hr observation for 24 hr later