Use a barometer to forecast wind direction and the character of upcoming weather.
Here are some general statements of wind-barometer indications that are generally applicable to all parts of the country:
- When the wind sets in form points between south and southeast and the barometer falls steadily, a storm is approaching from the west or northwest, and its center will pass near or north of the observer within 12 to 24 hours, with wind shifting to the northwest by way of south and southwest.
- When the wind sets in from points between east and northeast and the barometer falls steadily, a storm is approaching from the south or southwest, and its center will pass near or to the south of the observer within 12 to 24 hours, with winds shifting to northwest by way of north. The rapidity of the storm’s approach and its intensity will be indicated by the rate and amount of the fall in the barometer.
- As a rule, winds from the east quadrants and falling barometric pressure indicate foul weather, and winds shifting to the west quadrants indicate clearing and fair weather, but again there are exceptions and in some parts of the country these rules do not apply.
The following table generally summarizes wind and barometer indications in the United States. The amateur forecaster should modify the table in accordance with his or her own observations.
(Reduced to Sea Level)
|Wind Direction||Character of Weather Indicated|
|30.00 to 30.20, and steady||westerly||Fair, with slight changes in temperature, for one to two days|
|30.00 to 30.20, and rising rapidly||westerly||Fair, followed within two days by warmer and rain|
|30.00 to 30.20, and falling rapidly||south to east||Warmer, and rain within 24 hours.|
|30.20 or above, and falling rapidly||south to east||Warmer, and rain within 36 hours.|
|30.20 or above, and falling rapidly||west to north||Cold and clear, quickly followed by warmer and rain.|
|30.20 or above, and steady||variable||No early change.|
|30.00 or below, and falling slowly||south to east||Rain within 18 hours that will continue a day or two.|
|30.00 or below, and falling rapidly||southeast to northeast||Rain, with high wind, followed within two days by clearing, colder.|
|30.00 or below, and rising||south to west||Clearing and colder within 12 hours.|
|29.80 or below, and falling rapidly||south to east||Severe storm of wind and rain imminent. In winter, snow or cold wave within 24 hours.|
|29.80 or below, and falling rapidly||east to north||Severe northeast gales and heavy rain or snow, followed in winter by cold wave.|
|29.80 or below, and rising rapidly||going to west||Clearing and colder.|
|Note: A barometer should be adjusted to show equivalent sea-level pressure for the altitude at which it is to be used. A change of 100 feet in elevation will cause a decrease of 1 ⁄10 inch in the reading.|