ETA WEATHER MODEL

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ETA WEATHER MODEL
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ETA MODEL

• Used to forecast the weather as far out as 48
  hours
• Implementation of the ETA has been tracked by the
  weather-user community in order to determine
  significant model tendencies

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Horizontal Domain of the ETA

• Displays portions of the tropical Atlantic to
  include Puerto Rico on the eastern boundary, and
  extends west to include Hawaii on the western
  boundary.

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ETA Biases

• Cyclones east of the Rockies often not deep
  enough
• Too little convection in the Western US
• None to very little convective precipitation over
  mountains
• Over predicts convective precipitation in coastal
  regions
• RH fields too dry. Drier than NGM/AVN due to
  water held in model clouds
• Cut-off lows formed too far north off West Coast
• Ejects West Coast cut-offs too soon, but better
  than other models
• Moves dry line too quickly eastward out of the
  Plains
• Transport of moisture northward into the Plains
  too weak

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ETA Strengths All Regions

• Best NCEP model for quantitative precipitation
  forecast (QPF) except for convective
  precipitation over complex terrain in the West
• Provides representative reflection of
  divergent/convergent, heat transport through the
  boundary layer when it correctly predicts
  precipitation. (If precipitation is not
  accurately predicted, then boundary layer
  divergence/convergence is inaccurate)
• Useful in forecasting surface features in winter
  such as low-level boundaries
• Handles wind shifts better than other NCEP models

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ETA Strengths - Regional

• In the East
• Provides the best NCEP forecast of cold air
  damming and over-water flow off the Atlantic
  Coast
• Along the West Coast
• Usually correctly develops cut-off lows but
  possibly too far north and ejected too quickly
• Catches some of the Catalina Eddies over Southern
  California
• Does a reasonable job on placement and amount of
  orographic precipitation
• Over the Plains
• Handles the timing of Arctic air masses surging
  southward better than other NCEP models
• Handles penetration of cold air west of the
  Texas/New Mexico plains well compared to other
  NCEP models.

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ETA Weaknesses All Regions

• Little to no convective precipitation over the
  mountains
• Boundary level winds too weak and too smooth
• 850 mb winds too strong
• Poorly analyzes the marine boundary layer
• Does not resolve temperature gradients well
• Terrain resolution still insufficient to
  accurately forecast orographic precipitation
  placement and amounts
• Tends to maintain low-level moisture in the
  mountains after frontal passage in both the East
  and West

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ETA Weaknesses All Regions

• Soundings sometimes appear unrealistic because
• The convective scheme nudges the sounding toward
  the reference profile and can make it look too
  dry
• The model has a hard time depicting strong
  inversions
• Inversions, especially mountain/valley
  influences, not properly modeled
• Moisture fields underdone in the low-levels
• Problems initializing tropical systems
• Over forecasts strength of anticyclones
• Sometimes over develops low-level jet streams

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ETA Weaknesses - Regional

• In the East
• Sometimes tracks lows too far west along the East
  Coast when closed upper low approaches the coast
• High precipitation bias for heavy amounts during
  cold season
• Over the Rockies and in the West
• ETA sometimes too far south with leeside
  cyclogenesis
• High precipitation bias for light amounts during
  cold season
• Low precipitation bias during warm season

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ETA Weaknesses - Regional

• Over the Plains
• Often underplays precipitation associated with
  major convective complexes. Predicts rainfall
  maximum too far north because it cannot handle
  outflow boundaries
• High precipitation bias for light amounts over
  upslope area east of the Rockies and over the
  Central Plains
• Low precipitation bias during warm season for
  heavier amounts
• In the South
• Particularly wet in Florida

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Great Lakes Forecasting System provides data for
all of the Great Lakes, including experimental
wind and wave forecasts. The ETA Model Winds and
Great Lakes Waves use color coded maps and
barbs/arrows to describe forecasted wind
directions and speeds and wave heights and
direction. These models are usually accurate and
give a more detailed idea of forecasted
conditions around the Great Lakes.
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MESO ETA Model

• Forecasts weather up to 33 hours ahead

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Description of the Model

• The MESO ETA model is a hydrostatic model with a
  horizontal grid spacing of approximately 29 km
  and 50 vertical levels, with layer depths that
  range from 20 m in the planetary boundary layer
  to 2 km at 50 mb. The ETA coordinate was used in
  order to remove the large errors which are known
  to occur when computing the horizontal pressure
  gradient force, as well as the advection and
  horizontal diffusion, along a steeply sloped
  coordinate surface.

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Variables used in the Model

• The primary variables in the Meso Eta model are
  temperature, humidity, horizontal wind
  components, surface pressure, and turbulent
  kinetic energy.
• More recently, cloud water and ice have also
  become variables. A split integration approach,
  which is also used in the ETA model, is used in
  producing forecasts based on these quantities.

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Interaction between Tropical Storm Josephine and
a local Northeastern over North Florida had a
major influence on the precipitation, flow
structure, boundary layer wind damage, and
tornado generation associated with the storms
landfall.
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Sources

• http//www.comet.ucar.edu/nwplessons/etalesson2/ch
  aracteristicsbackground.htm
• http//www.cptec.inpe.br/etaweb/index.shtml
• http//www.srh.noaa.gov/jax/research/josy/josy2.ht
  ml
• http//www.srh.noaa.gov/jax/research/josy/paperjos
  ysurf.gif
• http//www.wrh.noaa.gov/wrh/96TAs/TA9606/ta96-06.h
  tml