How El Niño Might Affect Trout Fishing in the Mid-Atlantic

It’s December and dry flies are still catching trout; I even saw a few hoppers out the other day. This fall has been very out of the ordinary. In fact, according to the NOAA (National Oceanic and Atmospheric Administration), the month of October was the world’s warmest ever recorded for that month, and it was the warmest October in America since 1963. I’m not sure how other states have fared this past month, but it has been a strangely warm November as well. This fall/winter is drastically different from the one we had last year, and there’s a good explanation for it. No, this article is not about global warming or conspiracy theories, it’s meant to describe another weather phenomenon that might have a significant affect on fly fishing this winter… El Niño.

 

What is El Niño?

El Niño is really very simple, but the affects of one can be extraordinarily complex. El Niño is the name given to a period of above average temperatures in the tropical Pacific Ocean (near the equator). They are categorized using the Oceanic Niño Index (ONI), which averages the previous 3 months’ surface temperatures in a particular region of the Pacific. When the temperature averages are .5-.9° C above the historical average, a weak El Niño is present. A temperature increase of 1-1.4° C is a moderate El Niño, and an increase of more than 1.5 ° C above the norm results in a strong El Niño. El Niños usually occur every 2-7 years, but their intensities vary. The peak of the El Niño is during the winter and early spring, and that’s when the major affects of one become evident.

ONI readings from the past 50 years. Red indicates El Niños (courtesy of NOAA).

On a side note, La Niñas are the opposite of El Niños; they’re periods of abnormally cool surface temperatures in the Pacific Ocean. They can also bring strange weather patterns.

 

How does El Niño affect weather in the Mid-Atlantic?

At first glance it doesn’t seem like it would have much influence on the eastern part of the North American continent, but in reality it can have a big affect on the weather in this part of the world. For one, hurricanes in the Atlantic Ocean become less frequent (notice there haven’t been very many this year, and none have been very devastating to our eastern seaboard). In a normal, or moderate, El Niño year, the southeastern United States typically has a wetter winter, and the northeastern United States typically has a warmer winter.

Effects of a moderate El Niño year (courtesy of NOAA).

In a strong El Niño year, however, these ranges and intensities may increase. For example, during the 1997-98 El Niño, one of the strongest on record, the state of Virginia received about 10 more inches of precipitation than average. In fact, the southeastern portion of the United States had the wettest winter ever recorded in the 103 years prior. These states also had an above average temperature during that winter. The northeastern states had a fairly average year for precipitation, but it was the second warmest on record in the previous 103 years (“The El Niño Winter of ’97-98,” NOAA). It goes to show that a very strong El Niño can have incredible influences on the weather patterns here in North America.

 

Maps of how the ’97-98 winter ranked for each state (courtesy of NOAA).

 

What kind of El Niño are we experiencing?

The 2015-2016 El Niño already appears to rival the ’97-98 El Niño as one of the strongest ever recorded. The most recent ONI (August – October) is 1.7, indicating that this year is already considered a strong El Niño. There are parts of the Pacific where the surface temperature is over 5° C above normal, which is the highest ever recorded in such places.

A comparison of the current ONI to that of the very strong 1997 El Niño in one particular section of the Pacific (courtesy of The Weather Network).

 

What does that mean for fishing this winter/spring?

In the past, strong El Niños have brought a lot of precipitation and abnormally high temperatures to the east coast. If this year’s El Niño continues as expected, it’s safe to assume the winter of 2015-16 will have these characteristics as well.

Higher temperatures might mean insect activity continues throughout much of the winter months. The trout could be less lethargic than usual this winter and might continue to eat surface flies when available, instead of hunkering down in deep pools. In addition, the freestone streams that are usually off-limits due to being partly frozen in the winter may remain fishable.

Since the warm temperatures will melt the snow quickly, snow will probably not accumulate throughout the winter. Therefore, this spring will likely not have one giant thaw that melts all the accumulated snow and raises the rivers to absurd levels for usually about a week. Instead, the streams will remain at above average discharges right into the spring due to the increase in precipitation.

The high amount of precipitation will provide more dissolved oxygen and food for trout, perhaps making them more likely to feed. The greater discharge will definitely effect the hatching fry as well, for better or worse. Greater stream velocities could force the sac fry out of the safety of the redd, either killing the fish or making it easy prey for a larger predator. However, the greater amount of oxygen and food flowing downstream will no doubt help the tiny trout that stay in the nest survive their first winter.

The spring creeks and tailwaters will flow higher this winter too, bringing the big trout out of their hiding places to feed. This winter will be prime time for lunker hunting.

All in all, the forecast for this winter’s fishing is looking very good. Fishing for trout with a stimulator in a long sleeve t-shirt in January might not be too far of a stretch (of course, you might need to pack a rain jacket!). Don’t hang up your waders waiting for spring, the fish of the year might come early this year.

A big winter rainbow caught in high water.