Lecture 24 Weather Forecasting• What should I wear today?• How should the Forest Service fight a summer wildfire?• Should Jack go skiing this weekend?• Should Ace Hardware stock more umbrellas this fall?• When should Paul Bunyan plant his wheat?• How many snowplows does Seattle need?• For what rate should Allstate insure homes on the North Carolina coast?• Do we need to worry about global warming?...require weather/climate forecasts for today, a few days, months, decades.• How are forecasts made?• How good are they?• How good can they be?We focus mainly on midlatitude weather forecasts out to a week ahead, where most progress has bee...How are forecasts made?1. Current weather conditions observed around the globe (balloons, satellites, surface, aircraft,...2. Observations sent over Global Telecommunications System to weather centers (In US, National Ce...3. Center quality controls and analyzes observations.4. Computer model at center makes global or national weather forecast maps5. Center disseminates observations and forecast information to public and private agencies, such...6. Agencies use computer model maps and knowledge of local weather patterns to issue local and re...7. News media broadcast these forecasts.Time is of the essence. In a miracle of technology and communication, 1-3 day forecasts are typic...Weather ObservationsWeather is global, and requires global observations to forecast. Through the cooperation of 130 m...Data: (see ECMWF link on 101 weather web page for current example)Radiosondes -Wind, press.,temp., humidity profilesPilot Balloons -Wind profiles onlySatellitesGeostationary - cloud track winds, cloud heightsPolar orbiters - temperature profiles (1-2 km resolution)- humidity profiles (3-5 km resolution)- surface wind over oceanSurface ObservationsWeather reporting stations over landBuoysCommercial ships and aircraftNumerical Forecast Model• Atmospheric model uses mathematical equations to predict changes in temperature, humidity, pres...• The model is formulated in terms of the atmospheric state at a set of grid points, typically at...• Using the observations, with the prior forecast to fill in gaps, the model starts with its best...• The model equations are solved, stepping the forecast atmospheric state 5- 20 mins forward at a...• Billions of computations on the world’s most powerful supercomputers go into a several day fore...• Forecast maps (500 mb height, 850 mb temp., precipitation, etc.) printed each 12 hours into for...Forecast Model Grid• Gridpoints are at box corners.• Grid follows terrain.Some Current Forecast ModelsNCEPGlobal Forecast System (GFS) modelglobal, run 4x daily out to 16 days. Grid points spaced at 50 km (distance from Seattle to Tacoma).ETA modelCovers North America and adjacent regions, run out to 84 hours every 6 hours. Grid points spaced ...Runs in 2 hours.UW/ Seattle NWSMesoscale Model (MM5)Covers E Pacific, Western N America, run out to 72 hours every 12 hours. Grid points every 12 km ...ECMWF(European Centre for Medium-Range Weather Forecasts, England)Like GFS model, 25 km resolution(!), run out to 20 days using data from 12 GMT daily - most skill...Pacific NW topography for 36 km grid spacing(www.atmos.washington.edu under Weather/Climate Info: MM5)• Olympic Mts., Puget Sound are smoothed over. 12 km resolution is required for these features, w...How does forecaster turn maps into a forecast?• Local geography may be smeared out in model• Model often has small biases (too low temperatures, too much rainfall W of Cascades but not eno...• Model forecast not perfect; radar/satellite info may suggest improvement.The human forecaster has an important job:• Model-predicted surface temperatures must be adjusted, and local rainfall patterns and probabil...• Small-scale processes such as thunderstorms, valley fog or low cloud formation must be inferred...• Forecaster must make forecasts, weather warnings intelligible to the public for many zones acro...• If forecast appears systematically off, forecaster must use updated current weather information...Lecture 24 Weather Forecasting• What should I wear today?• How should the Forest Service fight a summer wildfire?• Should Jack go skiing this weekend?• Should Ace Hardware stock more umbrellas this fall?• When should Paul Bunyan plant his wheat?• How many snowplows does Seattle need?• For what rate should Allstate insure homes on the North Carolina coast?• Do we need to worry about global warming?...require weather/climate forecasts for today, a few days, months, decades.• How are forecasts made?• How good are they?• How good can they be?We focus mainly on midlatitude weather forecasts out to a week ahead, wheremost progress has been made.How are forecasts made?1. Current weather conditions observed around the globe (balloons, satellites,surface, aircraft, etc.).2. Observations sent over Global Telecommunications System to weather cen-ters (In US, National Centers for Environmental Prediction, or NCEP,Camp Springs, MD).3. Center quality controls and analyzes observations.4. Computer model at center makes global or national weather forecast maps5. Center disseminates observations and forecast information to public andprivate agencies, such as regional National Weather Service forecast offices(e.g. at Sand Point in Seattle).6. Agencies use computer model maps and knowledge of local weather pat-terns to issue local and regional forecasts.7. News media broadcast these forecasts.Time is of the essence. In a miracle of technology and communication, 1-3day forecasts are typically broadcast in US within 6 hours of the observationson which they are based.Weather ObservationsWeather is global, and requires global observations to forecast. Through thecooperation of 130 member countries, the UN World Meteorological Organi-zation ensures uniform observation procedures and transmission protocolsand free access to all available data.Data: (see ECMWF link on 101 weather web page for current example)Radiosondes -Wind, press.,temp., humidity profilesPilot Balloons -Wind profiles onlySatellitesGeostationary - cloud track winds, cloud heightsPolar orbiters - temperature profiles (1-2 km resolution) - humidity profiles (3-5 km resolution) - surface wind over oceanSurface ObservationsWeather reporting stations over landBuoysCommercial ships and aircraftNumerical Forecast Model• Atmospheric model uses mathematical