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I have a question about barometric pressure. I have a weather center that gives all the data, etc. Is there a specific pressure when it will rain? I have seen it rain at 30.00 and then at 29.85 it isn't raining. Is there a web site for barometric pressure? I tried several but they do not help. Any help you can give would be appreciated.

Posted August 26, 2007

MIKE MOSS SAYS:      P M, There is not a simple relationship between pressure and precipitation by which we can establish that it will rain if the pressure falls below a certain threshold or not rain above that same value. We can do a little better in relating the occurence of rapid or persistent pressure decreases to an enhanced likelihood of clouds and precipitation, and rapid or persistent increases in pressure to a trend toward dry weather, but even these do not have easily applied rules of thumb that will always accurately indicate whether it is raining or will soon rain. Instead, the barometer and its pressure readings become one small part of an overall weather analysis that includes temperature, humidity, wind speed and direction, cloud observations and trends, and ideally, maps showing the horizontal variability of all these elements, along with measurements at various heights from balloons and aircraft, and ideally some satellite and radar imagery, in order to make a more confident forecast.

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