A History of Modern Weather Forecasting

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A History of Modern Weather Forecasting
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The Stone Age

• Prior to approximately 1955, forecasting was
  basically a subjective art, and not very
  skillful.
• Observations were sparse, with only a few
  scattered ship reports over the oceans.
• The technology of forecasting was basically
  subjective extrapolation of weather systems, in
  the latter years using the upper level flow (the
  jet stream).
• Local weather detailswhich really werent
  understood-- were added subjectively.

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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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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

• This gives 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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NWP Becomes Possible

• By the 1940s there was an extensive upper air
  network, plus many more surface observations.
  Thus, a reasonable 3-D description of the
  atmosphere was possible.
• By the mid to late 1940s, digital programmable
  computers were becoming availablethe first..the
  ENIAC

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The Eniac
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First NWP

• The first successful numerical prediction of
  weather was made in April 1950, using the ENIAC
  computer at Maryland's Aberdeen Proving Ground
• The prediction was for 500 mb height, covered
  North America, used a two-dimensional grid with
  270 points about 700 km apart.
• The results indicated that even primitive NWP was
  superior to human subjective prediction. The NWP
  era had begun.

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Evolving NWP

• Early 50s one-level baratropic model
• Late 50s Two-level baroclinic QG model (just
  like Holton!)
• 1960s Primitive Equation Models of increasing
  resolution and number of levels.
• Resolution increases (distance between grid
  points decrease) 1958 380 km, 1985 80 km,
  1995 40 km, 2000 22 km, 2002 12 km

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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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The National Weather Service
Forecaster at the Seattle National Weather
Service Office