Weather and Trout

Most anglers agree that weather has an impact on trout fishing, What they tend not to agree on is how weather impacts trout fishing. Weather is complex and difficult to predict, as is trout behavior, but I’ll try to be as scientific as possible in this post.

Water Temperature

Water temperature is likely the most important environmental influence on trout behavior. For a good description of the ways water temperature affects trout, check out this blog post: Link, but for this discussion all you need to know is that trout feed most actively between 40-65 F and begin to suffer potentially lethal stress at 70 F.

So, how does weather affect water temperature?

Several factors come into play. The first, and most obvious, is air temperature. Air that is warmer than the water will warm it and air that is colder than the water will cool it. But air temperature is not the most important factor.

The transfer of heat between air and water is slow and can only take place at the waters surface. Sunlight plays a larger role in warming the water in streams, as it directly warms the water and stream bottom. This is why shade is vital to keep water temperatures below lethal levels in trout streams in warmer climates.

When planning a outing, it’s important to pay attention to both air temperature and sunlight. In winter, when water temperatures are cold, a sunny day can give trout the boost they need to feed. Daytime air temperature is less important than sun in winter, but it can pay to check the low temperature for the day before. Although warmer high temperatures are generally better for fishing, a cold night can cool the stream enough to negate the effects of the daytime temperature. For example, a day with a high of 32 following a nightly low of 30 will probably be more productive than a day with a high of 40 and a low of 20.

In the summer the sun can raise temperatures to dangerous levels, so poorly shaded streams should be avoided on sunny days, or at least at midday. High air temperatures can also cause temperature problems, but this is likely unless the day is unseasonably warm.

Feeding Activity

Different weather conditions can lead to wildly different feeding patterns in trout. For this discussion, I’ll consider three general conditions: Sunny, Overcast, and Rainy.

Sunny Days

The brighter the day, the more visible everything is. This means that both trout and their food sources are at higher risk of predation and are therefore less active. It also lets trout see your flies, line, and shadows more easily, increasing the risk of spooking a fish. That’s not to say it’s impossible to catch fish on a sunny day. Focus on riffled areas, where trout are less visible from above, and you’ll likely find fish.

Overcast Days

Overcast days are ideal for fishing. Trout are more active, and many insects are more likely to hatch. You also won’t cast a shadow, so the risk of spooking fish is much lower. The only exception is in winter, when water temperatures are often too low on cloudy days.

Rainy Days

If you can stand being outside, rainy days are even better than overcast days. All of the advantages of overcast days still apply, and the rain adds further benefits. Rain breaks up the surface of the water, making it more difficult for the fish to see you. This is great on flat spring creeks where fish usually won’t let you get close enough to cast without spooking. Rain also washes terrestrials into the stream, which results in active fish. The only potential downside of rain is that it can raise water levels to unfishable levels.

The last element of weather to which I pay attention is wind. It can be a bit of a wildcard. Although wind can break up the surface of the water and blow terrestrials into the water, it also makes casting difficult. Personally, I feel the negatives outweigh the positives on days with wind over 10 mph, but his is my last consideration.

Hopefully this helps in planning future trips!