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A History of Modern 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." .
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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 (sufficiently precise and repeatable) weather instruments became available
More and more people took observations….and some early networks were started
The problem: no way to rapidly communicate weather observations • This changed around 1845 with the invention of the telegraph
Weather Prediction Began • The essential approach…simple temporal 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 weather a weather forecast (including the term “probability”) to users and the public around 1870. 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."
Forecast Skill Stagnated in the late 1900s and early 20th century • Didn’t know what was happening over the oceans • Didn’t know what was happening aloft. • Could not predict the evolution of weather systems.
The Next Major Advance • The Norwegian Cyclone Model, around 1920
Norwegian Cyclone Model • Provided a coherent consistent picture of airflows, clouds, and precipitation of cyclones and fronts • Provided a model for frontal and cyclone evolution, aiding future prediction.
Next Major Advance: Upper Air Observations Became Available from Radiosonde in the 1920’s, 30s, and 40s
1940s: Upper Air Charts Using the New Data • Gave a 3D picture of what was happening • Learned how the upper flow steered storms, and thus provided a tool for forecasting cyclone movement.
Upper Level Chart
Summary I • Prior to approximately 1950, forecasting was basically a subjective art, and not very skillful. • The technology of forecasting was basically subjective extrapolation of weather systems, in the latter years using the upper level flow and the evolution described by the Norwegian cyclone model. • Local weather details—which really weren’t understood-- were added subjectively.
Numerical Weather Prediction • During this period, numerical weather prediction—forecasting future weather with digital computers-- became meteorologists’ central tool. • The advent of digital computers in the late 1940s and early 1950’s made possible the simulation of atmospheric evolution numerically. The Eniac The first programmable digital computer
Numerical Weather Prediction The basic idea is if you can describe the current state of the atmosphere (known as the initialization) , you can predict the future using the equations that describe the physics of the atmosphere.
The Initialization Using a wide range of weather observations we can create a three-dimensional description of the atmosphere.
Numerical Weather Prediction One of the equations used to predict the weather 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)
F = ma • The initialization gives the distribution of mass (how much air there is and where) and allows us to calculate the various forces. • Then… we can solve for the acceleration using F=ma • With the acceleration we can calculate the velocities in the future. • Similar idea with temperature and humidity but with different equations.
Numerical 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 over the Past 50 years • Faster computers and better understanding of the atmosphere, allowed a better representation of important physical processes in the models • Better and better resolution • 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
