Does a two-point spread between temperature and dew point mean that precipitation is inevitable?

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Dear Tom,

Years ago our Navy flying club instructor cautioned that a two-point spread between temperature and dew point meant that precipitation was inevitable. Would his metrics fair in today’s technological world?

Thanks,
Lane F. Schnotala,
Chicago

Dear Lane,

It would not. Let’s just say that precipitation is always inevitable, but not always imminent. Today or centuries ago, a small spread between the temperature and dew point may or may not lead to rain. In fair weather situations when the temperature and dew point converge, the result can be just dew, frost or fog and in some instances, none of the above. When low pressure approaches, it can be a totally different story and precipitation does break out. However, precipitation can occur when there is a large spread in the surface temperature and dew point, as long as saturation is occurring at cloud level.

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