A Brief History of Weather Forecasting

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A Brief History of Weather Forecasting
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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."

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By the late 1700s, reasonable weather instruments
became available
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More and more people took observations.and even
some early networks were started
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The First Weather Forecaster?
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The problem no way to rapidly communicate
weather observations

• This changed around 1845 with the invention of
  the telegraph

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First Real-Time Weather Maps
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Weather Prediction Began

• The key approachsimple extrapolation

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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
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• 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 735 a.m.

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• 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."

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The Next Major Advance

• The Norwegian Cyclone Model around 1920

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1940s The Upper Air Chart

• Gave a 3D picture of what was happening
• Upper flow steered storms

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Upper Level Chart
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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 wasnt practical then because there was no
  reasonable way to do the computations and
  sufficient data for initialization did not exist.

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Numerical Weather Prediction

• The advent of digital computers in the late 1940s
  and early 1950s 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.

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The Eniac
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Numerical Weather Prediction

• One such equation is Newtons 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!
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Numerical Weather Prediction
Using a wide range of weather observations we can
create a three-dimensional description of the
atmosphere known as the initialization
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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
  Fma
• But this gives us the future. With the
  acceleration we can calculate the velocities in
  the future.
• Similar idea with temperature and humidity.

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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.

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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.

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Forecast Skill Improvement
National Weather Service
Forecast Error
Better
Year
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Satellite and Weather Radars Give Us a More
Comprehensive View of the Atmosphere
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Camano Island Weather Radar
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1995-2003The 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.

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The National Weather Service
Forecaster at the Seattle National Weather
Service Office
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But even with all this improving technology, some
forecasts fail or are inadequate. Why?
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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.

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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 regionthe Pacific Ocean.

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3 March 1999 Forecast a snowstorm got a
windstorm instead
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Eta Model Sea Level Pressure 12 UTC 2 March 99
Major Initialization Errors
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Pacific Analysis At 4 PM 18 November 2003
Bad Observation
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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.
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Seascan Unmanned Aircraft
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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 initializationwell
  within observational error can have large
  impacts on the forecasts, particularly for longer
  forecasts.
• Not unlike a pinball game.

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• The Lorenz Diagramchaos
• Is not necessarily random

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A More Fundamental Problem

• Thus, there is fundamental uncertainty in weather
  forecasts that can not be ignored.
• Similarly, uncertainty in our model physics also
  produces uncertainty in the forecasts.
• We should be using probabilities for all our
  forecasts or at least providing the range of
  possibilities.
• There is an approach to handling this issue that
  is being explored by the forecasting
  communityensemble forecasts.

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Ensemble Prediction

• Instead of making one forecastmake manyeach
  with a slightly different initialization
• Possible to do now with the vastly greater
  computation resources that are available.

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Verification
The Thanksgiving Forecast 2001 42h forecast
(valid Thu 10AM)
SLP and winds

• Reveals high uncertainty in storm track and
  intensity
• Indicates low probability of Puget Sound wind
  event

1 cent
11 ngps
5 ngps
8 eta
2 eta
3 ukmo
12 cmcg
9 ukmo
6 cmcg
4 tcwb
13 avn
10 tcwb
7 avn
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Ensemble Prediction

• Can use ensembles to provide a new generation of
  products that give the probabilities that some
  weather feature will occur.
• Can also predict forecast skill!
• It appears that when forecasts are similar,
  forecast skill is higher.
• When forecasts differ greatly, forecast skill is
  less.

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Ensemble-Based Probabilistic Products