A Brief History of Weather Forecasting The Beginning Weather Sayings Red Sky at night sailor s delight Red sky in the morning sailor take warning Mare s tails and mackerel scales make tall ships take in their sails Clear moon frost soon Halo around the sun or moon rain or snow soon Rainbow in the morning gives you fair warning When the stars begin to huddle the earth will soon become a puddle By the late 1700s reasonable weather instruments became available More and more people took observations and even some early networks were started The First Weather Forecaster The problem no way to rapidly communicate weather observations This changed around 1845 with the invention of the telegraph First Real Time Weather Maps Weather Prediction Began The key approach simple extrapolation Ol Probs Cleveland Abbe Ol Probabilities who led the establishment of a weather forecasting division within the U S Army Signal Corps Produced the first known communication of a weather probability to users and the public Professor Cleveland Abbe who issued the first public Weather Synopsis and Probabilities on February 19 1871 On May 7 1869 Abbe proposed to the Cincinnati Chamber of Commerce to inaugurate such a system by publishing in the daily papers a weather bulletin which shall give the probable state of the weather and river for Cincinnati and vicinity one or two days in advance Cleveland Abbe released the first public weather forecast on September 1 1869 Following the signing by President Ulysses S Grant of an authorization to establish a system of weather observations and warnings of approaching storms on February 19 1871 Abbe issued the first official public Weather Synopsis and Probabilities based on observations taken at 7 35 a m An early example of a report Synopsis for past twenty four hours the barometric pressure had diminished in the southern and Gulf states this morning it has remained nearly stationary on the Lakes A decided diminution has appeared unannounced in Missouri accompanied with a rapid rise in the thermometer which is felt as far east as Cincinnati the barometer in Missouri is about four tenths of an inch lower than on Erie and on the Gulf Fresh north and west winds are prevailing in the north southerly winds in the south Probabilities emphasis added it is probable that the low pressure in Missouri will make itself felt decidedly tomorrow with northerly winds and clouds on the Lakes and brisk southerly winds on the Gulf The Next Major Advance The Norwegian Cyclone Model around 1920 1940s The Upper Air Chart Gave a 3D picture of what was happening Upper flow steered storms Upper Level Chart The Development of NWP Vilhelm Bjerknes in his landmark paper of 1904 suggested that NWP was possible A closed set of equations existed that could predict the future atmosphere primitive equations But it wasn t practical then because there was no reasonable way to do the computations and sufficient data for initialization did not exist Zur Anzeige wird der QuickTime Dekompressor Foto JPEG ben tigt Numerical Weather Prediction The advent of digital computers in the late 1940s and early 1950 s made possible the simulation of atmospheric evolution numerically The basic idea is if you understand the current state of the atmosphere you can predict the future using the basic physical equations that describe the atmosphere The Eniac Numerical Weather Prediction One such equation is Newton s Second Law F ma Force mass x acceleration Mass is the amount of matter Acceleration is how velocity changes with time Force is a push or pull on some object e g gravitational force pressure forces friction This equation is a time machine Numerical Weather Prediction Using a wide range of weather observations we can create a three dimensional description of the atmosphere known as the initialization Numerical Weather Prediction Observations give the distribution of mass and allows us to calculate the various forces Then we can solve for the acceleration using F ma But this gives us the future With the acceleration we can calculate the velocities in the future Similar idea with temperature and humidity Numerical Weather Prediction These equations can be solved on a threedimensional grid As computer speed increased the number of grid points could be increased More and thus closer grid points means we can simulate forecast smaller and smaller scale features We call this improved resolution A Steady Improvement Faster computers and better understanding of the atmosphere allowed a better representation of important physical processes in the models More and more data became available for initialization As a result there has been a steady increase in forecast skill from 1960 to now Forecast Skill Improvement National Weather Service Forecast Error Better Year Satellite and Weather Radars Give Us a More Comprehensive View of the Atmosphere Camano Island Weather Radar 1995 2003 The computers models become capable of simulating forecasting local weather As the grid spacing decreased to 15 km and below it became apparent that many of the local weather features could often be simulated and forecast by the models The National Weather Service Forecaster at the Seattle National Weather Service Office But even with all this improving technology some forecasts fail or are inadequate Why Problems with the Models Some forecasts fail due to inadequacies in model physics How the model handles precipitation friction and other processes Example too much precipitation on mountain slopes Intensive work at the UW to address this problems Some forecasts fail due to poor initialization i e a poor starting description of the atmosphere This is particularly a problem for the Pacific Northwest because we are downstream of a relatively data poor region the Pacific Ocean 3 March 1999 Forecast a snowstorm got a windstorm instead Eta 48 hr SLP Forecast valid 00 UTC 3 March 1999 Eta Model Sea Level Pressure 12 UTC 2 March 99 Major Initialization Errors Pacific Analysis At 4 PM 18 November 2003 Bad Observation The problem of initialization should lessen as new observation technologies come on line and mature New ways of using or assimilating the data are also being developed Seascan Unmanned Aircraft A More Fundamental Problem In a real sense the way we have been forecasting is essentially flawed The atmosphere is a chaotic system in which small differences in the initialization well within observational error can have large impacts on the