I should add that on occasion, the sky cover cannot be seen due to a low-level obstruction such as heavy fog, heavy rain, blowing snow, etc. In the sample station model below on the right, the circle is mostly filled in, corresponding to a "mostly cloudy" sky with 6/8 cloud coverage. The greater the cloud coverage that exists, generally the larger the portion of the circle that is filled in. Interpreting sky coverage on the station model is fairly intuitive, as the circle in the station model serves as the "pie chart" that shows the cloud coverage. The weather observer can't determine the coverage or ceilings of clouds because low-level fog, haze, or smoke obscures the sky. Partly Cloudy or Partly Sunny (5/8) to Mostly Cloudy (6/8 or 7/8) Official sky coverage categories (and fractional coverage measures) versus plain-language sky descriptions.
Cloud ceiling is not included in the station model, but it is particularly important for airplane pilots. When the sky is broken or overcast, weather observations will include the corresponding cloud ceiling, which is simply the height of the base of a broken or overcast layer of clouds. Picturing " overcast" conditions (8/8 coverage) is straightforward. When the sky is nearly overcast except for a few breaks, forecasters refer to the cloud coverage as breaks in the overcast (abbreviated as " BINOVC"). " Scattered" clouds (3/8 to 4/8 cloud coverage) correspond to a partly cloudy or partly sunny sky, with " broken" clouds (5/8 to 7/8 cloud coverage) describing a partly cloudy or partly sunny (5/8 coverage) to mostly cloudy (6/8 to 7/8 coverage) sky. Clear conditions (0/8 cloud coverage) constitute a perfectly sunny sky, while a " few" clouds (1/8 to 2/8 coverage) represent mostly sunny conditions. The "pie" that makes up the sky coverage observation is divided into 8 sections. Most weather forecasters don't want to get drawn into such an argument of semantics, so when it comes to quantifying the coverage of the sky by clouds, they rely on a specific "pie-chart" system that leaves little room for debate (see table below). With this usage, a partly sunny day is actually cloudier than a partly cloudy day. Some folks use "partly sunny" to emphasize that there will be a bit more clouds than sun, and use "partly cloudy" to emphasize that there will be a bit more sun than clouds. But, in practice, some forecasters use these terms differently because the word "partly" is somewhat vague, so it's not clear cut.
Let me start with the age old question: "Which phrase do you think describes a cloudier sky? Partly sunny or partly cloudy?" The National Weather Service defines partly sunny and partly cloudy as essentially the same, with the caveat that we wouldn't use "partly sunny" at night, of course. Sky Coverage: Sky coverage simply describes the portion of the sky covered by clouds.
Mountain weather indicator clouds clear how to#
As I did with temperature, dew point, visibility, and present weather, I'll briefly describe each variable and its common units of measurement (if applicable), and then describe how to interpret it on a station model. I've outlined the part of the station model that includes this information in the sample on the right, but note that the station model also includes information about air pressure, which we'll mostly ignore for now and come back to later on. We're going to continue tackling the information contained in the station model, and now we're going to turn our attention to cloud coverage and wind direction and speed.
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