Barometric pressure is the earliest warning a boater gets that the day is about to change, and it is readable from the helm without any forecast at all. It is the weight of the atmosphere pressing down at your location, reported in millibars or in inches of mercury.
The trend matters far more than the reading. Falling pressure often signals an approaching low and the unsettled weather that comes with it, while rising pressure usually means conditions are improving and settling. A rapid change in either direction is the one to take seriously: pressure that drops quickly can mean severe weather is close, and that is the moment to shorten the trip rather than watch it develop.
Pressure alone will not tell you the wind speed or the sea state, so treat it as a confirmation of what the forecast already said. When the forecast calls for deteriorating conditions and your barometer is falling to match, believe it. When the two disagree, err toward the more conservative option and get into protected water while you still have the choice.
Anglers watch the same trend for different reasons, since feeding behaviour often shifts around a pressure change and the hours before a front can fish very differently from the hours after it. We cover that in our guide to how pressure trends affect fishing.
