• http://aviationweather.gov/adds/metars/description.php for METARs help page
• http://aviationweather.gov/adds/metars/description2.php for METARS basic decoder
• http://aviationweather.gov/adds/metars/description_ifr.php

• Flight category definitions:
  

  Category	Ceiling		Visibility
  Low Instrument Flight Rules LIFR* (magenta sky symbol)	below 500 feet AGL	and/or	less than 1 mile
  Instrument Flight Rules IFR (red sky symbol)	500 to below 1,000 feet AGL	and/or	1 mile to less than 3 miles
  Marginal Visual Flight Rules MVFR (blue sky symbol)	1,000 to 3,000 feet AGL	and/or	3 to 5 miles
  Visual Flight Rules VFR+ (green sky symbol)	greater than 3,000 feet AGL	and	greater than 5 miles
  *By definition, IFR is ceiling less than 1,000 feet AGL and/or visibility less than 3 miles while LIFR is a sub-category of IFR. +By definition, VFR is ceiling greater than or equal to 3,000 feet AGL and visibility greater than or equal to 5 miles while MVFR is a sub-category of VFR.

  
  
• Cloud coverage symbols:
  
  Automated stations report "CLR" when clouds may exist above 12,000 feet so a square is used to represent this uncertainty whereas an unfilled circle is used for "SKC" which a human reports the sky is completely clear overhead. The abbreviation "OVX" is unofficial but ADDS uses it here to indicate the sky is obscured which is the case when a METAR reports vertical visibility and no cloud information.
• General Flight Weather Descriptions

  IFR means instrument flight rules conditions. IFR includes ceilings less than 1,000 feet and/or visibility less than three statute miles.

  MVFR stands for marginal visual flight rules conditions, including ceilings from 1,000 to 3,000 feet and/or visibility between three and five statute miles.

  VFR is visual flight rules conditions when ceilings are higher than 3,000 feet and visibility is greater than five statute miles.

  Terms describing amount of sky covered by clouds

  Clear means there are no clouds.

  Few means that clouds cover one-eighth to two-eighths of the sky.

  Scattered means that clouds cover three-eighths to four-eighths of the sky.

  Broken means clouds cover five-eighths to seven-eighths of the sky.

  Overcast means clouds cover more than seven-eighths of the sky.

  Terms describing shower or thunderstorm coverage

  ISOL represents isolated weather, such as single thunderstorm cells.

  WDLY SCT means widely scattered. In other words, less than 25 percent of a given area is affected.

  SCT or AREAS means that the showers or thunderstorms are scattered and 25 to 54 percent of a given area is affected.

  NMRS or WDSPRD means that the showers or thunderstorm cells are numerous or widespread, affecting 55 percent or more of a given area.

   

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 Dick Fechter
(507) 775-7686
FPS at 44RF.com (at=@)
139 13th St NE
Byron, MN 55920