Information Shown on Composite Weather Maps:
North Pacific and North American Overviews

Upper-Air Maps (500 and 300 millibars)

The composite weather maps for the 500 and 300 millibar pressure surfaces (which correspond roughly to 18,000 ft. and 32,000 ft., respectively) show what's going on in the middle and upper troposphere, respectively. These maps are generated twice daily and display the following information:
  1. Contours of geopotential height (that is, the height above sea level of a constant-pressure surface, in this case shown at intervals of 60 meters).
    The analyses come from either the eta or aviation (AVN) forecast model initializations performed twice daily by the National Centers for Environmental Prediction (NCEP--formerly the National Meteorological Center, NMC).

    [Note: The domain of the eta-model extends only a modest distance into the eastern Pacific, whereas the AVN model domain covers the globe. However, the eta-model output typically arrives at least five hours earlier than the AVN model output, so in the interests of timeliness, the eta model output is shown for a few hours every day before the more extensive AVN output replaces it.]

  2. A gray-scale infrared satellite image from the GOES-West satellite (for the North Pacific view), or a composite of that image plus an image from the GOES-East satellite (for the North American view), recorded as near as possible to the time of the analyses in (1) above.

  3. Plots of weather data recorded by balloon-borne rawinsondes launched at the same time as the analyses in (1) above. The weather data include:

Surface and Sea-Level Map

The composite weather maps for the surface are generated twice daily and display the following information:
  1. Contours of sea-level pressure (at intervals of 4 millibars).
    The analyses comes from the eta-model or aviation (AVN) model initialization performed twice daily by the National Centers for Environmental Prediction (NCEP--formerly the National Meteorological Center, NMC).

    [Note: The domain of the eta-model extends only a modest distance into the eastern Pacific, whereas the AVN model domain covers the globe. However, the eta-model output typically arrives at least five hours earlier than the AVN model output, so in the interests of timeliness, the eta model output is shown for a few hours every day before the more extensive AVN output replaces it.]

  2. A gray-scale infrared satellite image from the GOES-West satellite (for the North Pacific view), or a composite of that image plus an image from the GOES-East satellite (for the North American view), recorded as near as possible to the time of the analyses in (1) above; and

  3. Plots of surface weather data, recorded at the same time as the analyses in (1) above. The weather data include:

The time and date appearing on these maps is in Universal Time Coordinates (UTC), formerly known as Greenwich Mean Time (GMT). (See comments about time labels for more information.)
For information about reading some of the meteorological information on these maps, refer to the key to weather-station plots and general description of visible and infrared satellite images.

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