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."."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 First Weather Forecaster?

The problem: no way to rapidly communicate weather observationsThis changed around 1845 with the invention of the telegraph

First Real-Time Weather Maps

Weather Prediction BeganThe essential approachsimple temporal extrapolation

Atmospheric Model

Ol ProbsProfessor Cleveland Abbe, who issued the first publicWeather 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 weather a weather forecast (including the term probability) to users and the public around 1870.

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 centuryDidnt know what was happening over the oceansDidnt know what was happening aloft.Could not predict the evolution of weather systems.

The Next Major AdvanceThe Norwegian Cyclone Model, around 1920

Norwegian Cyclone ModelProvided a coherent consistent picture of airflows, clouds, and precipitation of cyclones and frontsProvided a model for frontal and cyclone evolution, aiding future prediction.

Next Major Advance: Upper Air Observations Became Available from Radiosonde in the 1920s, 30s, and 40s

1940s: Upper Air Charts Using the New DataGave a 3D picture of what was happeningLearned how the upper flow steered storms, and thus provided a tool for forecasting cyclone movement.

UpperLevelChart

Summary IPrior 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 detailswhich really werent understood-- were added subjectively.

1950-1965: The Advent of Modern Numerical Forecasting

Numerical Weather PredictionDuring this period, numerical weather predictionforecasting future weather with digital computers-- became meteorologists central tool. The advent of digital computers in the late 1940s and early 1950s made possible the simulation of atmospheric evolution numerically.

The EniacThe first programmabledigitalcomputer

Numerical Weather PredictionThe 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.

Using a wide range of weather observations we can create a three-dimensional description of the atmosphere.The Initialization

Numerical Weather PredictionOne of the equations used to predict the weather is Newtons 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!

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=maWith the acceleration we can calculate the velocities in the future.Similar idea with temperature and humidity but with different equations.F = ma

Numerical Weather PredictionThese 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 yearsFaster computers and better understanding of the atmosphere, allowed a better representation of important physical processes in the modelsBetter and better resolutionMore and more data became available for initializationAs a result there has been a steady increase in forecast skill from 1960 to now.

Forecast Skill ImprovementForecastErrorYearBetterNational Weather Service

**********