Wind

Temperature variations at different levels of the atmosphere produce winds. Just above and below the equator, winds typically blow from east to west—these are the trade winds that powered the sailing ships of premodern mercantile fleets. North of the 40th parallel, which runs across North America from Redding, California, through Denver, Indianapolis, and Philadelphia, winds blow predominately west to east. These are the westerlies that come out of the Sierras and Rockies to whip across the western plains, gathering momentum as they cross the Central region and sweep over the Great Lakes to the east. Directional winds create water currents. And, although most anglers overestimate the importance of wind-induced currents, there’s no question that understanding the effects of prevailing winds can be useful in locating bass.

Coriolis Force

When to westerlies is added the Coriolis force, which causes air and water to deflect clockwise in the northern hemisphere, anglers’ common observation that currents move to the right of wind direction is readily explained. In immense lakes like Ontario and Superior, the current bends as much as 45 degrees. On smaller lakes, the angle of current deflection is smaller; currents tend to follow main-lake shorelines and to circle large bays in the direction of prevailing winds. Limnologists studying 9,600-acre, 80-foot-deep Lake Mendota, Wisconsin, have found that currents there are deflected about 20 degrees to the right of the wind. It’s safe to assume, then, that in most lakes, the current’s deflection is slightly to the right of the prevailing wind.

What are the likely effects of this discovery on locating and catching largemouth bass?

Rebound currents

Rebound current affects largemouths’ position near middepth structural elements. Fish in shallow water usually face into shallow surface current. But fish holding deeper than about 5 feet are likely to face into a reverse current—in other words, in the opposite direction. The direction that they’re facing affects your presentation. Largemouths ambush or chase their prey, so sneaking up on them from behind, without factoring in current direction, isn’t likely to be successful. When bass face into the rebound current, which moves in the direction opposite to the wind, your presentation should move toward or quarter in front of them.

Main-lake structures that constrict the flow of wind-generated currents often attract baitfish and bass. A hump that rises to within a few feet of surface can compress and accelerate wind-driven currents enough to stimulate avid feeding. On smaller reservoirs, wind currents are less important. Coves on these bodies of water usually have no detectable wind currents at all, unless winds last for several days. When this happens, floating plankton may concentrate near downwind shores. Such banquets attract baitfish. Their uninvited guests are bass.

Shoreline currents

When currents hit shorelines, they, too, are deflected clockwise. In turn, this deflection affects fishes’ positions and locations. Suppose you’re fishing a plateau reservoir in warm weather. Wind blowing toward the shore produces a right-moving current. If you follow the shoreline drop-off to the right until you encounter a bar, the inside turn on the current side of the bar is likely to hold active bass. If this scenario occurs in early spring or late fall, however, when water is cold and bass aren’t active, the inside turn on the current side is apt to be empty. Largemouths are likely to be on the backside of the point’s tip, away from the cold current. Use your knowledge of current deflection and rebound currents to locate bass.

Barometric Pressure

One of the most persistent traditions in fishing is that barometric pressure controls the activity level of fish. Like a lot of theories, this one is basically untestable and therefore unprovable, because whatever effects barometric changes may have on largemouths are compounded by changes in wind, temperature, and sky conditions.

When barometric pressure drops, cloud cover typically increases and weather fronts bring wind changes. When pressure rises again, blue skies, sunlight, and cooler, drier winds predominate. Largemouths definitely respond to such complexes of weather-related events—but which ones? No scientific studies have been able to demonstrate conclusively that barometric pressure alone is responsible for any changes in largemouths’ behavior. One study often cited is Dr. Carl Quertermus’ and George Mitchell’s 1982 observation that largemouth bass in shallow water (41⁄2 feet or less) are more likely to be found under docks when barometric pressure is high.

Atmospheric pressure usually rises after passage of a cold front, and with it return clear skies, bright sunlight, and increased ultraviolet radiation. Fish holding shallow at such times may instinctively move under docks to hide in the shade. Are they responding to barometric pressure by seeking out a new equilibrium depth, adjusting to stronger light levels, or making some other accommodation to changing conditions?