All fish can sense changes in barometric pressure. This is especially true of largemouth bass. In fact, bass grow aggressive as the pressure drops and become downright careless during a light rain. Even those monster bass that anglers sometimes see but seldom catch can be tricked into striking during a sudden summer shower. All you need is a willingness to get wet.
Low Light Levels
Even the biggest largemouth bass feels exposed and vulnerable in direct sunlight. On the brightest days these fish burrow into weeds or head for deep, dark water where they are all but inactive and unapproachable. Yet, as daylight fades with the approach of a storm, even big bass are lulled into a sense of security. When that happens, they may strike suddenly and unexpectedly.
Not long ago I camped beside a Wisconsin lake that was said to be brimming with 3-pound largemouths. My partner and I fished the lake for two days, but all we caught were stunted fish. Then, on the third morning, the sky turned pewter as low, scudding clouds swept in before a storm. All of a sudden, big bass began to bite.
They struck our floating Rapalas wherever we cast. Each time we tossed a lure, a bass would grab it and explode like a bomb. For two days we had fished the same weedy bay without catching a decent fish. Now with the approach of rain, bedlam was breaking.
By noon, birch trees were snapping like whips in the wind. Beyond our sheltered bay, foaming combers crashed against rocky shores. Raindrops as big as buckshot began to fall. Finally, when distant lightning flashed, we pointed our canoe toward camp. But during those hours before the storm, we caught and released dozens of bass. A few of these barometric bass topped 3 pounds.
Diminishing light was not the only reason why the largemouths went on a rampage that morning. Although the fishing picked up as soon as the gray clouds rolled in-creating a false dusk with the low light levels bass associate with feeding-the biggest largemouths didn’t strike until raindrops pelted the water. The rain roiled the lake’s transparent surface and turned it cloudy. This concealed us from those bass that otherwise would have hung back in deep cover at the approach of a boat. Instead, the fish didn’t see our shadows and ventured out from cover to strike our lures.
Sudden turbidity is also a signal that foraging will soon be difficult. Aware of this, the bass go on a feeding binge.
In summer, when temperatures sizzle, warm water turns the most voracious largemouths indolent. When these fish feed-if they feed at all-they tend to inhale whatever morsels of food pass by their snouts, instead of darting out to strike at a meal. An aggressive attack requires too much effort in warm water. But the climatic changes accompanying a falling barometer can cool a lake’s surface water, and the action of raindrops pelting a lake quickly increases oxygen levels. This sudden mix of cooler water and increased oxygen triggers activity. It lures bass out of hiding places, drawing them up to the surface where they are easier to find and tempt.
An approaching storm after several days of stable weather affects bass in other ways, too. For instance, bass become finicky eaters during steady weather. Cheney Lake is a bass lake near my home that I regularly fish. During long spells of stable weather, the bass here tend to strike black Hula Poppers-and then only at dusk. Yet, just before a cloudburst, and for a little while afterward, the bass in Cheney will attack any lure you toss.
A sudden shower turns bass into gluttons. Worms, grubs, and mice get washed into the water; insects float in windrows along sheltered shores; baitfish get jittery, following and feeding on the flotsam of land-based insects. With all this food suddenly there for the taking, bass become opportunists-they strike at the largest meeal they can nab.
Tactics and Tackle
During a light but constant rain, the best place to fish is right up against the shore with the wind in your face. Shorelines flood quickly, pulling bass up from deep water into partially submerged weeds and other vegetation. Here, the rain and wind attract baitfish. Minnow imitations, like Rapalas, catch big bass in these circumstances.
During an intermittent drizzle, fish for bass in inlet bays. Rain washes bait into the streams that enter those bays, and bass will be most active where the discolored stream water mixes with the lake. Rooster Tail spinners or a Mepps Comet Mino work well in this situation.
Minnows and minnow imitations are the preferred bait when it rains. I discovered this in watching a biologist collect stomach-content samples from various fish species. The chub he collected had been feeding on terrestrials; the bass he examined had been feeding on chub. When it rains, minnows actively feed on insects washed into lakes. Where minnows are active, bass will be ravenous.
If you fish with plugs and spinners, stick to colors and styles that resemble minnows; if you prefer jigs with live bait, fluorescent colors catch the most largemouths on rainy days. In water where weeds are not a problem, a Whistler jig is deadly when the barometer falls.