Definition
A pair of values reported together in a surface aviation weather observation, expressed in degrees Celsius. Temperature is the current ambient air temperature. Dew point is the temperature to which the air must be cooled, at constant pressure and water vapor content, for it to become saturated and water vapor to begin condensing. The smaller the spread between the two, the closer the air is to saturation.
Plain English
Two numbers reported side by side in a weather observation. The first is how warm the air is right now. The second is how cool the air would need to get before moisture starts forming. When the two numbers are close, the air is nearly wet enough to produce clouds, fog, or visible moisture.
Context Anchor
Seen in aviation weather reports for an airport, especially when checking current conditions before a flight.
Derivation
Dew point comes from the everyday observation that dew forms on grass overnight when the air cools to a certain temperature. That temperature is the point at which dew appears. Pairing it with the current temperature gives a quick read on how close the air is to that condition.
Why Pilots Care
The spread between temperature and dew point shows how close the air is to saturation, directly affecting visibility, fog formation, cloud ceilings, and icing risk during takeoff, landing, and flight.
Grounding Statement
If the air temperature drops to the dew point, moisture in the air can start becoming visible as fog, mist, cloud, or dew.
Intuition Check
Temperature/dew point does not mean a temperature range. It means two separate readings: the current air temperature first, then the dew point second.
Example Sentence 1
The METAR showed a temperature/dew point of 18/17, so the pilot expected fog to form shortly after sunset.
Example Sentence 2
Before departure the pilot checked the temperature/dew point spread at the destination to judge the chance of low ceilings.