A high-pressure system trailing a cold front is the best of worst situations a bass angler can face. Without fail, this force of nature will temporarily shut down fishing activity and leading the problem is changing barometric pressure.
Ask yourself, what does barometric pressure have to do with bass? Does it affect only shallow-water fish? Or does it reach to deepwater bass, as well? Ask these questions, and everybody has an opinion based on personal angling observations.
For better understanding cold fronts, anglers need to know what barometric pressure is and how it can affect fishing activity.
Simply, barometric pressure is nothing more than a measurement of pressure, which is nothing more than the weight of air above a certain point — in this case a lake or body of water.
Generally, a front passes through the area and pressure rises. Cold air is denser and therefore heavier than warm air. When a cold front comes through, heavier air replaces lighter air. Also, dry air is heavier and moist air is lighter. There are other factors in the atmosphere that produce pressure changes, but if you reduce everything to simple terms, pressure is nothing more than the weight of air above a certain point.
Theoretically, low pressure should prevail on a lake prior to a front, with a moist south wind blowing. As the front approaches barometric pressure will rise, with drier and colder air pushing moist air out.
In simple terms, pressure will be lower ahead of a front and may stabilize before the front passes. The pressure increases to a certain point, then stabilizes again until a second front passes.
With the basics of barometric pressure in mind, anglers need to know how it relates to water and how it can affect bass. Simply, as barometric pressure rises there is an increased pressure in water.
How deep does the effect of barometric pressure reach?
Ever notice that the deeper spots of Melones and McClure seem to keep biting? Studies have shown that normal rises in barometric pressure rarely affect layers of water more than 20 feet deep. Pressure changes in deeper water are caused by falling temperatures.
From studies of tracking fish before and after barometric changes, many experts have come to believe deeper fish are less affected by pressure and fish weighing more than 7 pounds show little regard to pressure changes.
A dramatic barometric change affects all bass. It takes about a 25-degree temperature change to affect the larger fish, and it lasts only a short time. High winds also will affect them, as will large amounts rain.
Basically, you have two kinds of bass. Smaller fish are generally more shallow and go dormant after a cold front. They will hold motionless near a stump or brush pile for long periods of time until the barometric pressure begins to drop. The studies have shown smaller fish ceased activities along weed lines, while the larger fish don't seem to break their daily routine of cruising along several hundred yards near a weed line in 8 feet of water.
Unless the shallows are colder than 50 degrees, bass will move to them and feed on a daily basis.
Basically, bass weighing more than 5 pounds do not break the pattern from one season to the next. They go to the same place to feed, and cruise the same territory each day, 12 months a year. The only modification will be how shallow they go. If shallows are in the 40s they cruise deeper 16 to 22-foot ledges.
For me, these pressure changes are dominating factors. It affects deepwater fish as it does shallow fish. Several times I've graphed large groups of fish holding over deep structure and caught them good the day before a front. The following day, after a front moved and those bluebird skies signaled a tough day ahead, I chased the same fish. They backed off structure, refusing all baits. Then, after the front passed, the fish sometimes moved back to structure and fed maybe 15 minutes, compared to hours before the front.
If it's not high barometric as the front passes, what else can move fish that deep off structure quickly?
Just some thoughts that may help us continue to learn the changes of bass during this stormy fall winter periods.