Signs {weather sign} that forecast fair weather are evening rainbow or deep-blue sky color, even between clouds. Signs that forecast rain are gray and lowering sunset, green or yellow-green sky at sunset, red sunrise with clouds lowering later, sun dog around Sun or Moon after fine weather, morning rainbow, or sky whiteness. Clouds that look like lenses indicate high winds. Light and dark clouds {mackerel sky, weather} indicate rain. Low dark clouds indicate stormy weather.
Prolonged air contact with surface gives air {air mass}| same temperature and humidity as surface. Air masses {tropical mass} over Sahara Desert are warm and dry. Tropical masses in tropics are warm and wet. Air masses {polar mass} over plains of Canada or Siberia are cold and dry. Cold air masses make high pressure. High-pressure air masses can stay offshore, blocking east-west wind flow.
Atmosphere pressure {air pressure}| depends on temperature, water content, friction, centrifugal force, and flow. Cooler air has higher pressure. Spinning air can have higher pressure. Air with less water has higher pressure. Air blocked by mountains has higher pressure. Air-pressure patterns vary by latitude. High-pressure swirling cells are more near poles and in subtropics. Low-pressure cells are more in temperate zones.
Difference, between average daily temperature and 20 C, times number of days in month {degree-day}, directly relates to fuel to use to keep warm.
Warm air mass makes low pressure {depression, atmosphere}|, because it is less dense than cold air.
Weather forecasting {meteorology}| depends on atmosphere, humidity, pressure, and wind photographs and measurements.
A halo {sun dog}| around Sun or Moon after fine weather forecasts rain.
Weather maps {weather map} {map, weather} can show isotherms and isobars.
Equal-pressure points {isobar} can be on weather maps.
Equal-temperature points {isotherm} can be on weather maps.
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Date Modified: 2022.0225