A History of Modern Weather Forecasting

A History of Modern Weather
The Beginning: Weather Sayings
"Red Sky at night, sailor's delight. Red sky in the morning, sailor take
"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
• This changed around 1845 with the
invention of the telegraph
First Real-Time Weather Maps
Weather Prediction Began
• The essential approach…simple temporal
Atmospheric “Model”
“Ol Probs”
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,
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 fourtenths 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
• Didn’t know what was happening aloft.
• Could not predict the evolution of weather
The Next Major Advance
• The Norwegian Cyclone Model, around
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.
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
• Local weather details—which really weren’t
understood-- were added subjectively.
The Advent of Modern Numerical
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
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
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)
This equation is a time machine!
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 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 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
• As a result there has been a steady increase in
forecast skill from 1960 to now.
Forecast Skill Improvement
NCEP operational S1 scores at 36 and 72 hr
over North America (500 hPa)
National Weather Service
S1 score
"useless forecast"
36 hr forecast
72 hr forecast
Error 35
10-20 years
"perfect forecast"