by Richard Ziert
Solving myths are sometimes just matters of bringing two or more known things together in a new, more understandable way. Cold Fronts and their add-on changes in atmospheric pressure – thus, an alleged exaggerated bite and shutdown of fish activity, is one such common myth.
Barometric pressure alone does not change quickly enough, nor have primary effects, to practically turn bass or any other fish on or off. However, it is one of the ingredients in the overall process of fish location features. Associated air and water temperature, time of year/day, cloud cover, wind direction and speed, humidity and yet to be confirmed effects of the dew point also affect fishing conditions. The rate and amount of change in barometric pressure is insignificant compared to what’s going on below the surface because of secondary relationships.
Depending on the geographic altitude of the lake, because water is thicker/more dense, than air, average water pressure at the 33 foot depth is equal to the pressure of two Air Atmospheres at the surface. Higher altitudes will change the depth noted. That means in part that if atmospheric pressure were to play a role affecting that first 33 feet of water the effect is greater at the surface than it is at its bottoming out point.
Consider for a moment that an average normal value for barometric pressure is about 30 inches (mercury). Normal strong high pressure is about 30.70 inches. The powerful atmospheric lows of hurricanes, can reach down to 28 inches or less. The difference between these two “normal” conditions (2.7 inches of barometric pressure) is equal to about .09 atmospheres. The barometric pressure difference from a simple passing cold front is only about .06 atmospheres. That .06 atmospheres of pressure, based on the 32 foot example to double the surface pressure, amounts to a depth just barely over a foot and a half from the surface downward, and that is the only layer of water that can reasonably or practically be affected by normal cold fronts. The dynamics of all weather and all temperatures, all locations, etc, can again nullify the exact effect.
That reference to “all temperatures” includes the temperature of the entire water column. Colder water is denser, therefore the denser or more viscous the water the harder it is to move it. Early and late in the year water is colder at the surface. Throughout the remaining seasons, until the lake turns over, water is colder as it goes deeper. During the spring of the year lake water warms from the top down. The water column gets colder at approximately 2 degrees per foot of depth. Waves in and of themselves alter shallow water column water pressure with their peaks and valleys. The combination of surface chop and or waves then can sometimes completely offset any atmospheric pressure changes as they might apply at or beneath the surface.
Meteorologists and Biologists know how fish seemingly respond to these day-to-day barometric changes. They haven’t quite hit the nail on the head as yet – but “deep down” (pun intended), they know.
At some time in the late spring or early summer the surface layer of water biologists call a Littoral Zone fully matures as to water temperature. In that case that layer is pretty much uniform as to temperature. Deeper than the Littoral Zone the temperature gets colder and colder as more depth is added until the development of the thermocline (if any) comes into play. Through and beneath the thermocline rapid cold temperature changes occur. You will note how it all works as depicted in the following chart.
Thirty to thirty-five feet is the reasonably deepest level at which most anglers target their “clear” fresh water quarry. The term 'Clear Water' is subjective to where you fish. But for our purposes clear water is when a white lure disappears when dropped overboard at about 16-17 feet. Note again that in this example that 16-17 feet is the Littoral Zone. That 33 foot marker depth is also where direct, penetrating light diminishes greatly (but not completely). Those 33 feet down from the surface represents where Thermoclines set up shallower and progress deeper; reaching their average deepest point in our examples clear water column during the height of summer.
From the surface down, the first 16-17 feet of water, or the average depth at which weeds bottom out mid lake in clear water (again a light penetration condition) is scientifically known as the Littoral Zone mentioned earlier and the most productive, most overall stable layer of water; season to season. This layer is stable in terms of water temperature and the early signs of fish reaction to the elements. As lake water becomes stained all reactions appear shallower. Some weeds grow deeper or shallower depending on how, where, and when– lake specific - photosynthesis can occur. Photosynthesis can occur deeper than the Littoral Zone, but the deeper photosynthesis, thereby dissolved oxygen process is more plankton related rather than weeds. Depending on light penetration, various forms of plankton and their associated oxygen production and transport can sink from near the surface to beneath the thermocline as well as move laterally due to current and wind.
Biologists have observed underwater fish movements during cold front weather exchanges. The result is and always will be open to doubt. The reason for this involves The Universal Law of Large Numbers. That law states: In order to get an accurate or finite picture of outcome, you must first have a very large number of test cases which are the same in detail to draw information from (thousands). Unfortunately, biologists can only measure a few fish at a time, one body of water at a time, and one location within that one lake; precision or anything near it can not be achieved. For our practical on the water purposes, it’s safe to say active to inactive fish during cold front conditions is likely no better than 50/50. But what we can conclude for sure is the known movement of predator / prey relationships coupled with associated light penetration.
All fish don’t feed at the same time. Some fish are full of food “in the moment”. Fish are in fact responding to natural urges, earliest formed instincts, coupled with experience, determining where they can be located during and around such times? While some fish may be digesting a full meal, with few exceptions, given the slam dunk opportunity, hungry, healthy, and eager fish, like all other opportunistic predators, eat/strike, lean toward becoming gluttons at all times and places and that’s all there is to that.
There should be very few practicing anglers among us that don’t know the effects of an approaching cold front. Just to make it crystal clear to everyone, here’s a short version of all the goings-on.
Just before the front is upon us the sky is usually clear and bright. Then, more or less, suddenly, air pressure changes. If we are quiet enough, attentive enough, we can actually feel the change in the pressure on our ear drums just like it happens when we gain or reduce altitude in aircraft. On the water, I’ve experienced this ear drum fact to where a half hour passed before the visible storm was overhead. Then, well out in front of the approaching clouds the wind picks up and darker sky’s follow. The preceding, heavier wind, growing stronger and stronger, provides more and more exaggerated surface water chop and waves. That surface chop in turn makes for a darker underwater environment; a greater underwater flicker and wave effect camouflaging underwater fish movement. This source signals what is to come and fish everywhere are vitally aware of and conditioned to that opportunity.
The closer the front comes, the more frenzied the feeding spree. Sometimes into the edge of the storm and marginally beyond, hungry fish continue the blown up bite. At some point fishermen get off the lake in fear for their lives in that rough weather. That doesn’t mean the bite stops. It means we are smart enough to not risk our lives in catching fish.
During and after the storm front the sky is usually dark with clouds and the wind is much stronger than before. While exceptions exist, typically the cloud cover/winds peter out over an average of 1- 3 days; returning weather conditions to not unlike those before the storm. What are left is blue bird clear sky’s and depending on the time of day and year, glaring/direct light penetration. The greater the cold front storms size in territory covered and the faster the movement, the greater the effect is squeezed into narrower parameters.
Let’s look at “Light Penetration” cause and affect on fish during these times. From experience, Sunny, Clear Sky’s, little or no wind, tell us not all but most bass are either, on or near the bottom and/or at a depth or place where light penetration is less. When clouds approach, many fish including prey rise in the water column to one degree or another, suspend in the water column, or gradually approach the edges of cover from the inside out. Evidence for this is found in part when we see that more or less calm water surfaces bites occur best in low light especially early and late in the day.
Bass eyes use rods and cones much like humans. Like you and me, bass can not adjust their pupils to varying levels of light quickly. Think about the old Navy Submarine Movies you have seen where the U-Boat surfaces at night and the lights in the sub are changed from white to red for some time before the outer hatch is opened and crewmen go above. They did that change to have their eyes adjust quickly to the dark.
Biologists have found bass take as much as 15-20 minutes to adjust to changing light conditions. If bass are positioned in darker places before the darker parts of the storm gets to them, little or no adjustment at all is needed. Some smaller prey fish species take longer than bass to adjust to abrupt low light conditions; giving bass an advantage; heightening search and capture effectiveness.
If hungry fish are found more on the move, higher off the bottom, more near the surface and/or at the edges of structure or cover during those dark times, they are camouflaged there to have a better sight and vibration advantage at capturing prey. Prey fish are there because low light hides their movement. That and the prey also are conditioned to know the flow of food elements (plankton or what have you) is increased; more on the move laterally and vertically. The longer the sky stays dark, the more predator/prey directional movement occurs. With a natural need to use penetrating light to photosynthesize, plankton, rise upward in the water column with darker skies– plankton then sink with brighter skies - plankton eaters (bait fish and the majority of minnows otherwise) follow the source of their food.
If we are good enough anglers to know where our target fish are during times of plenty, and what happens when a cold front moves through, we then are able to pinpoint objective spots to fish. Knowing the average time it takes for conditions to get back to “normal” we then can pick out the areas and depth levels to explore and increase our catch.
To possibly make this even more clear, the following illustration may help. The orange ovals, black and blue rectangles below show the real effects of cold front movement.
Atmospheric Pressure and Cold Front Myths
by Richard Ziert
Barometric pressure alone does not change quickly enough, nor have primary effects, to practically turn bass or any other fish on or off. However, it is one of the ingredients in the overall process of fish location features. Associated air and water temperature, time of year/day, cloud cover, wind direction and speed, humidity and yet to be confirmed effects of the dew point also affect fishing conditions. The rate and amount of change in barometric pressure is insignificant compared to what’s going on below the surface because of secondary relationships.
Depending on the geographic altitude of the lake, because water is thicker/more dense, than air, average water pressure at the 33 foot depth is equal to the pressure of two Air Atmospheres at the surface. Higher altitudes will change the depth noted. That means in part that if atmospheric pressure were to play a role affecting that first 33 feet of water the effect is greater at the surface than it is at its bottoming out point.
Consider for a moment that an average normal value for barometric pressure is about 30 inches (mercury). Normal strong high pressure is about 30.70 inches. The powerful atmospheric lows of hurricanes, can reach down to 28 inches or less. The difference between these two “normal” conditions (2.7 inches of barometric pressure) is equal to about .09 atmospheres. The barometric pressure difference from a simple passing cold front is only about .06 atmospheres. That .06 atmospheres of pressure, based on the 32 foot example to double the surface pressure, amounts to a depth just barely over a foot and a half from the surface downward, and that is the only layer of water that can reasonably or practically be affected by normal cold fronts. The dynamics of all weather and all temperatures, all locations, etc, can again nullify the exact effect.
That reference to “all temperatures” includes the temperature of the entire water column. Colder water is denser, therefore the denser or more viscous the water the harder it is to move it. Early and late in the year water is colder at the surface. Throughout the remaining seasons, until the lake turns over, water is colder as it goes deeper. During the spring of the year lake water warms from the top down. The water column gets colder at approximately 2 degrees per foot of depth. Waves in and of themselves alter shallow water column water pressure with their peaks and valleys. The combination of surface chop and or waves then can sometimes completely offset any atmospheric pressure changes as they might apply at or beneath the surface.
Meteorologists and Biologists know how fish seemingly respond to these day-to-day barometric changes. They haven’t quite hit the nail on the head as yet – but “deep down” (pun intended), they know.
Thirty to thirty-five feet is the reasonably deepest level at which most anglers target their “clear” fresh water quarry. The term 'Clear Water' is subjective to where you fish. But for our purposes clear water is when a white lure disappears when dropped overboard at about 16-17 feet. Note again that in this example that 16-17 feet is the Littoral Zone. That 33 foot marker depth is also where direct, penetrating light diminishes greatly (but not completely). Those 33 feet down from the surface represents where Thermoclines set up shallower and progress deeper; reaching their average deepest point in our examples clear water column during the height of summer.
From the surface down, the first 16-17 feet of water, or the average depth at which weeds bottom out mid lake in clear water (again a light penetration condition) is scientifically known as the Littoral Zone mentioned earlier and the most productive, most overall stable layer of water; season to season. This layer is stable in terms of water temperature and the early signs of fish reaction to the elements. As lake water becomes stained all reactions appear shallower. Some weeds grow deeper or shallower depending on how, where, and when– lake specific - photosynthesis can occur. Photosynthesis can occur deeper than the Littoral Zone, but the deeper photosynthesis, thereby dissolved oxygen process is more plankton related rather than weeds. Depending on light penetration, various forms of plankton and their associated oxygen production and transport can sink from near the surface to beneath the thermocline as well as move laterally due to current and wind.
Biologists have observed underwater fish movements during cold front weather exchanges. The result is and always will be open to doubt. The reason for this involves The Universal Law of Large Numbers. That law states: In order to get an accurate or finite picture of outcome, you must first have a very large number of test cases which are the same in detail to draw information from (thousands). Unfortunately, biologists can only measure a few fish at a time, one body of water at a time, and one location within that one lake; precision or anything near it can not be achieved. For our practical on the water purposes, it’s safe to say active to inactive fish during cold front conditions is likely no better than 50/50. But what we can conclude for sure is the known movement of predator / prey relationships coupled with associated light penetration.
All fish don’t feed at the same time. Some fish are full of food “in the moment”. Fish are in fact responding to natural urges, earliest formed instincts, coupled with experience, determining where they can be located during and around such times? While some fish may be digesting a full meal, with few exceptions, given the slam dunk opportunity, hungry, healthy, and eager fish, like all other opportunistic predators, eat/strike, lean toward becoming gluttons at all times and places and that’s all there is to that.
There should be very few practicing anglers among us that don’t know the effects of an approaching cold front. Just to make it crystal clear to everyone, here’s a short version of all the goings-on.
The closer the front comes, the more frenzied the feeding spree. Sometimes into the edge of the storm and marginally beyond, hungry fish continue the blown up bite. At some point fishermen get off the lake in fear for their lives in that rough weather. That doesn’t mean the bite stops. It means we are smart enough to not risk our lives in catching fish.
During and after the storm front the sky is usually dark with clouds and the wind is much stronger than before. While exceptions exist, typically the cloud cover/winds peter out over an average of 1- 3 days; returning weather conditions to not unlike those before the storm. What are left is blue bird clear sky’s and depending on the time of day and year, glaring/direct light penetration. The greater the cold front storms size in territory covered and the faster the movement, the greater the effect is squeezed into narrower parameters.
Let’s look at “Light Penetration” cause and affect on fish during these times. From experience, Sunny, Clear Sky’s, little or no wind, tell us not all but most bass are either, on or near the bottom and/or at a depth or place where light penetration is less. When clouds approach, many fish including prey rise in the water column to one degree or another, suspend in the water column, or gradually approach the edges of cover from the inside out. Evidence for this is found in part when we see that more or less calm water surfaces bites occur best in low light especially early and late in the day.
Bass eyes use rods and cones much like humans. Like you and me, bass can not adjust their pupils to varying levels of light quickly. Think about the old Navy Submarine Movies you have seen where the U-Boat surfaces at night and the lights in the sub are changed from white to red for some time before the outer hatch is opened and crewmen go above. They did that change to have their eyes adjust quickly to the dark.
Biologists have found bass take as much as 15-20 minutes to adjust to changing light conditions. If bass are positioned in darker places before the darker parts of the storm gets to them, little or no adjustment at all is needed. Some smaller prey fish species take longer than bass to adjust to abrupt low light conditions; giving bass an advantage; heightening search and capture effectiveness.
If we are good enough anglers to know where our target fish are during times of plenty, and what happens when a cold front moves through, we then are able to pinpoint objective spots to fish. Knowing the average time it takes for conditions to get back to “normal” we then can pick out the areas and depth levels to explore and increase our catch.
To possibly make this even more clear, the following illustration may help. The orange ovals, black and blue rectangles below show the real effects of cold front movement.
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