By Dr. Hal Schramm

Ever hear someone say, “It’s the only day I’ve got to fish, and a stinkin’ cold front is going to blow through the night before”? Maybe you even said it yourself, or at least thought it. I’m not about to dismantle the all-time most-accepted reason for lock-jaw bass and no-fish days, but let’s take an honest look at reasons why cold fronts often wreak havoc on the bass bite.

Bright, bluebird skies often follow major cold fronts, and one explanation I’ve heard for a tough bite post-cold front is “the bright light hurts bass’ eyes.” No doubt, the sun is bright when cloudless skies follow a cold front, and it’s true that bass have neither eyelids nor an iris to regulate light into their eyes. But, unlike anglers that can’t find shade fishing a deep ledge in the middle of the lake, the bass can move. If the bright light really “hurts” their eyes, the bass can move into aquatic weeds or the shadow of a log or a bluff bank. Moving deeper also reduces light.

A variation of the “bright-light-hurts-their-eyes” reasoning is the greater amount of UV light. True, cold fronts are often followed by clear air and low humidity, and the UV index is topped out. Apply sunblock early and often. However, most UV light is absorbed in the upper few feet of the water column. There are a couple studies that suggest fish may use UV light for feeding, but none that indicated UV light reduces feeding.
bone fish
Another piece of dock-talk wisdom is that the change in pressure causes discomfort. Cold fronts mean barometric pressure change from the low pressure that draws the cold front in to high barometer behind the front. Except for infrequent events like hurricanes and tropical storms, barometric pressure usually ranges from about 990 millibars, or 29.2 inches of mercury, to 1030 millibars, or 30.4 inches of mercury. Any way you report it, the result is the same—the change in barometric pressure after a cold front is only a change of about 4 percent.

Can fish detect this? Probably. Any fish with a swim bladder—and that includes bass-- has a built-in pressure-detecting organ.

Let’s do some simple math. Water is heavy stuff, and atmospheric pressure increases one atmosphere for every 10 meters—approximately 33 feet—increase in depth. The 4 percent increase in pressure that a fish would experience with the passage of a major cold front equates to the same pressure change a fish would experience moving down in the water column about 16 inches. And if the pressure change does make the bass uncomfortable, all it has to do is move up a few inches in the water column to be subjected to the same pressure as before the front passed. Maybe it’s just the pressure change that turns bass off, but it’s a pretty safe bet that the “discomfort factor” isn’t what changes the fish’s behavior.

Cold fronts are called cold fronts because the air temperature drops. The chilly air cools the water, and now we have something that the bass can detect and that might modify their behavior. However, there is fallacy to this reasoning, too. Without going into a discourse on water temperature-density relationships, the surface water temperature does decline after a cold front, but a single night of temperatures 15 or 20 degrees below normal doesn’t change the temperature of the whole lake or reservoir. Again, to sidestep the rather complex thermodynamics of water, think how long it takes your favorite lake to cool off just a few degrees in the fall or to warm up in the spring. Declining temperature doesn’t explain the post-cold front funk, either.

Now that I’ve poked holes in (and a little bit of fun at) dock-talk wisdom that supposedly accounts for the all-time best excuse for not catching fish, is it even true that bass don’t bite after a cold front? Tournament catch stats don’t show rises and falls with cold fronts or barometric pressure. It doesn’t matter what the weather pattern is, tournament winners keep catching 25-plus pound sacks.

There is one way that some cold fronts may adversely affect fishing and catching. Typically cooler temperatures and a strong north wind follow the cold front. It’s hard to control a bass boat in 3-foot waves. And if it’s winter, the cold is painful, and that impairs fishing efficiency. Yes, anglers (unlike bass) do feel pain.

Add it all up, the evidence indicates that cold fronts have a much greater effect on anglers than they do on bass.

About the author: Dr. Hal Schramm is a professor in the Department of Wildlife and Fisheries at Mississippi State University. He’s a frequent contributor to this website and many publications on science topics. He is a respected authority on bass fishing and the science behind our favorite activity.