Barometric Pressure and Fishing: What Actually Matters

What the number on the barometer is

Air pressure is reported in inches of mercury (inHg) on US weather broadcasts and in millibars, the same thing as hectopascals (hPa), on weather maps; NOAA gives standard sea-level pressure as 29.92 inHg, or 1013.25 hPa. Because pressure drops with height, weather stations convert their readings to what they would be at sea level, so that towns at different elevations can be compared. Pressure also rises and falls twice a day on its own, with lows around 4 a.m. and 4 p.m. and highs around 10 a.m. and 10 p.m.; the larger swings on top of that come from passing weather systems.

Pressure is a sign of the weather on its way

NOAA's guide to weather maps notes that cold fronts extend from low-pressure systems, never from highs, and that pressure can differ sharply from one side of a front to the other. In NOAA's description of a typical passage, thunderstorms arrive just ahead of the cold front, and once it has passed the wind turns to the northwest, the temperature drops and the sky clears. A barometer that is falling usually means a low and its weather are getting closer; a rise after a front comes with the cooler, clearer air behind it. Most of what anglers attribute to pressure is bound up with those changes in wind, cloud, rain and temperature.

What our score does with the barometer

The daily score on every water page of this site uses a fixed pressure rule, so you can check any report against it. We read the forecast sea-level pressure at 6 a.m. and at 6 p.m. local time and compare the two. A drop of more than 1.5 hPa (about 0.04 inHg) counts as falling, a rise of more than 1.5 hPa as rising, and anything in between as steady. Because the twice-daily pressure cycle repeats every 12 hours, two readings taken 12 hours apart sit at the same point in it, so the comparison mostly reflects the weather system. A day starts at 3 out of 5. Falling pressure adds a point, but only when the chance of rain is under 60%, because a front that arrives as a downpour is a weather problem. Rising pressure takes a point away, but only when cloud cover is under 30% (the latest reading for today, an estimate from the forecast sky for other days), because the bluebird conditions behind a front are part of the effect anglers report. Other rules for wind, heat and cold can move the score as well.

What studies have found

The evidence that pressure itself changes how fish feed is thin. Researchers who analyzed 13 years of compulsory creel records from Escanaba Lake, Wisconsin, included the daily pressure trend among their weather variables; for walleye and muskellunge it carried little weight in any of their models, while who was fishing, with what bait, and how much of the population had already been caught mattered most. The authors also wrote that they knew of no published study supporting the idea that storm fronts change catch rates. A small Bemidji State University laboratory study ran 12 feeding trials with yellow perch at rising, falling and steady pressure and found no significant effect on how much they ate. Treat the barometer as a forecast of the weather, not as a switch on the fish.

Depth changes pressure far more than weather does

NOAA notes that water pressure increases by one atmosphere, the whole weight of the air above sea level, for every 33 feet of depth in the ocean. By that ratio, a 10 hPa change in air pressure equals the change a fish feels by moving roughly 4 inches up or down. That does not prove fish ignore the barometer, but it is a reason to doubt that the number on the dial is what they respond to. The light, wind and temperature changes that come with a front are larger and easier to measure.

Species guides → · Walleye →

Bass, and the number everyone asks for

More people arrive here asking what pressure is best for bass than for any other species, so here is the straight answer: our score does not change by species, and we found no study that identifies a best reading. The sea-level correction is one reason a single figure cannot work. The National Weather Service defines station pressure as the actual pressure at the site and sea-level pressure as a correction of it, and the figures in weather reports are the corrected value, so a reading of 29.95 inHg is not the pressure on the water at Lake Mead or Lake Okeechobee. What can be compared between lakes is the direction and speed of the change, and that is what our score reads.

Largemouth bass → · Smallmouth bass →

Reading pressure on our pages

Every water page prints the current sea-level pressure in hPa from the Open-Meteo forecast model, which reports pressure reduced to mean sea level, along with the falling, steady or rising verdict from the 6 a.m. to 6 p.m. comparison. Weather apps and NOAA Weather Radio give the same quantity in inHg. Watch the trend the evening before and the morning of your trip, and read it alongside the wind, cloud and rain forecast on the same page.

Any water's live pressure → · How to read a fishing report →

Common questions