A Brief History of Weather ForecastingThe Beginning: Weather SayingsBy the late 1700s, reasonable weather instruments became availableMore and more people took observations….and even some early networks were startedThe First Weather Forecaster?The problem: no way to rapidly communicate weather observationsFirst Real-Time Weather MapsPowerPoint PresentationWeather Prediction BeganSlide 10“Ol Probs”Slide 12Slide 13The Next Major Advance1940s: The Upper Air ChartSlide 16The Development of NWPSlide 18Numerical Weather PredictionThe EniacSlide 21Slide 22Slide 23Slide 24A Steady ImprovementForecast Skill ImprovementSatellite and Weather Radars Give Us a More Comprehensive View of the AtmosphereSlide 281995-2003+ The computers models become capable of simulating/forecasting local weather.Slide 30Slide 31Slide 32Slide 33Slide 34But even with all this improving technology, some forecasts fail or are inadequate. Why?Problems with the ModelsSome forecasts fail due to poor initialization, i.e., a poor starting description of the atmosphere.Slide 38Slide 39Slide 40The 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.Slide 42Slide 43A More Fundamental ProblemSlide 45Slide 46Slide 47Ensemble PredictionSlide 49Slide 50Slide 51Slide 52A Brief History of Weather ForecastingThe 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 availableMore and more people took observations….and even some early networks were startedThe First Weather Forecaster?The problem: no way to rapidly communicate weather observations•This changed around 1845 with the invention of the telegraphFirst Real-Time Weather MapsWeather Prediction Began•The key approach…simple extrapolation“Ol Probs”Professor Cleveland Abbe, who issued the first public“Weather Synopsis and Probabilities” on February 19, 1871Cleveland 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.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 19201940s: The Upper Air Chart•Gave a 3D picture of what was happening•Upper flow steered stormsUpperLevelChartThe 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” benötigt.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 EniacNumerical Weather PredictionOne such equation is Newton’s Second Law:F = maForce = mass x accelerationMass is the amount of matterAcceleration is how velocity changes with timeForce is a push or pull on some object (e.g., gravitational force, pressure forces, friction)This equation is a time machine!Using a wide range of weather observations we can create a three-dimensional description of the atmosphere… known as the initializationNumerical 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 PredictionNumerical Weather Prediction•These equations can be solved on a three-dimensional 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 ImprovementForecastErrorYearBetterNational Weather ServiceSatellite and Weather