A History of Modern Weather Forecasting

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A History of Modern 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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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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L. F. Richardson An Insightful But Unsuccessful
Attempt

• In 1922 Richardson published a book Weather
  Prediction by Numerical Process that describes an
  approach to solving the primitive equations
  solving the equations on a grid using finite
  differences.

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L. F. Richardson

• He attempted to make a numerical forecast solving
  the equations using a mechanical calculator
• Unfortunately, the results were not good,
  probably because of problems with his initial
  conditions.
• He imagined a giant theater filled with human
  calculators
• So NWP had to wait until a way of doing the
  computations quickly was developed and more
  dataespecially aloft became available.

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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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The Last Piece of the Puzzle

• Meteorologist realized that useful numerical
  weather predictions were possible using a
  simplified equation set that were easier to
  solve.
• The Barotropic Vorticity Equation (conservation
  of absolute vorticity) was suggested as a first
  step

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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 NWS

• Early 50s one-level barotropic 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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NWP Improvements in the Later 20th Century

• Better resolution
• Rapidly increasing data for initialization from
  weather satellites, radars, more surface
  observations, and other sources.
• Better models better numerics and physics

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Forecast Skill Improvement
National Weather Service
Forecast Error
Better
Year
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The Advent Of Statistical Post-Processing

• In the 1960s and 1970s, the NWS developed and
  began using statistical post-processing of model
  outputknown to most as Model Output
  StatisticsMOS.
• The idea models have systematic biases..why not
  remove them based on past performance.
• Also, might be able to statistically add the
  effects of local features not resolved by the
  model.

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MOS

• Based on linear regression Ya0 a1X1 a2X2
  a3X3
• MOS is available for many parameters and time and
  greatly improves the quality of most model
  predictions.

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1990-2003The 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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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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A More Fundamental Issue

• The work of Lorenz (1963, 965, 1968) demonstrated
  that 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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A More Fundamental Problem

• Similarly, uncertainty in our model physics also
  produces uncertainty in the forecasts.
• Lorenz is a series of experiments demonstrated
  how small errors in initial conditions can grow
  so that all deterministic forecast skill is lost
  at about two weeks.
• Talked about the butterfly effect

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• The Lorenz Diagramchaos
• Is not necessarily random

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Probabilistic NWP

• To deal with forecast uncertainty, Epstein (1969)
  suggested stochastic-dynamic forecasting, in
  which forecast errors are explicitly considered
  during model integration, but this method was not
  computationally practical.
• Another approach, ensemble prediction, was
  proposed by Leith (1974), who suggested that
  prediction centers run a collection (ensemble) of
  forecasts, each starting from a different initial
  state. The variations in the resulting forecasts
  could be used to estimate the uncertainty of the
  prediction. But even the ensemble approach was
  not tractable at this time due to limited
  computer resources.

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Ensemble Prediction

• To create a collection of ensembles one can used
  slightly different initializations or different
  physics.
• By the early 1990s, faster computers allowed the
  initiation of global ensemble prediction at NCEP
  and ECMWF (European Centre for Medium Range
  Weather Forecasts).

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Ensemble Prediction

• During the past decade the size and
  sophistication of the NCEP and ECMWF ensemble
  systems have grown considerably, with the
  medium-range, global ensemble system becoming an
  integral tool for many forecasters. Also during
  this period, NCEP has constructed a higher
  resolution, short-range ensemble system (SREF).

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The Evolving Forecasting Problem

• Prior to 1955, humans did everything--subjectivel
  y forecast at all scales.
• Between 1955 and 1980 numerical weather
  prediction essentially took over synoptic
  forecasting. Humans were left with deciding
  between models or modifying (often
  unsuccessfully) the computer guidance).
• Humans retained the role of translating synoptic
  guidance to the mesoscale/microscale.
• Model Output Statistics (MOS) became competitive
  with human forecasters during the 1980s.

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Evolving Forecasting

• By around 1990, large scale forecasts had gotten
  very good for scales gt 1000 km for 0 to 48h
• Starting to consistently get the big storms
• But humans still crucial for local forecasting,
  interpreting imagery, and providing guidance on
  the reliability of forecasts.
• During the past ten years high resolution (or
  mesoscale) NWP has begun to make inroads in
  taking over mesoscale prediction.
• The ability to produce probabilistic forecasts
  using ensembles is improving quickly and should
  become a central element in NWP during the next
  decade.

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Sometimes humans even degrade the forecast if
they are not careful
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Ivars Seafood Mukilteo Restaurant Hit by 50-60
mph winds--A surge down the Strait.
"We were featuring fresh crab right on our plates
last night" Bob Donegan, Vice President of
Ivars
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The computer forecast models correctly forecast
the winds.
UW MM5 24-h forecast

• White (red) areas indicate sustained winds
  exceeding 46 (32) mph, gusts would be higher

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NATIONAL WEATHER SERVICE SEATTLE WA 330 PM PST
TUE OCT 28 2003 WAZ006gt008-291215- EVERETT AND
VICINITY-SEATTLE METROPOLITAN AREA-TACOMA
AREA-INCLUDING THE CITIES OF...BELLEVUE-EDMONDS-IS
SAQUAH...PUYALLUP 330 PM PST TUE OCT 28
2003 .TONIGHT...SHOWERS THIS EVENING...MAINLY
SEATTLE SOUTHWARD... BECOMING SCATTERED
OVERNIGHT. LOWS IN THE LOWER 40S. SOUTHWEST WIND
10 TO 20 MPH SOUTH OF SEATTLE...NORTHWEST WIND 10
TO 20 MPH SEATTLE NORTHWARD.