The Yellowstone area is subject at any time to violent weather changes, but especially so in the month of June. Two days ago we were enjoying near 70 degree temperatures. That night it rained, and by yesterday morning it was snowing. That kind of swift change can cause serious changes in water levels and temperature. See the two charts below. The first shows water flows on the Firehole River, the second water temperature. What had been a pattern of smooth, gradual reduction in flow levels and consistent daily temperature fluctuations were upset dramatically by the arrival of rain, snow, and cold.
Experienced anglers know that insect activity controls trout feeding activity. And they know, too, that weather plays a vital role in controlling insect activity. It was apparent from looking at these charts yesterday morning that things were not going to be the same on the Firehole as they had been. For the previous six days, beginning sometime between 9:00 a.m. and 10:00 a.m. we had enjoyed good hatches and lots of rising trout. The activity generally lasted until between 1:30 p.m. and 3:00 p.m. (There are many micro-habitats on the Firehole, hence the range of starting and ending times.)
Yesterday, knowing that things would be different, I arrived to the river at 2:15 p.m. My car thermometer read 42 degrees. When I checked the water, it was 56. Dark, heavy clouds drizzled rain. The river appeared lifeless. Not a single bug hatching, not a fish moving. Over the years, I’ve seen the Firehole shocked by weather many times. At the very least, emergences are delayed. Sometimes they don’t happen at all. You never know for sure. Patience is called for on these occasions, which admittedly can tax even the anglers that understand the situation. (I had guessed I might be early for the expected hatch of Baetis and Pale Morning Duns. At least I could take my time rigging up, which I did. I don’t handle things well when I arrive to a river with the fish already rising.)
On days like this, many fishermen will have already fished for hours. They usually arrive in the morning, gear up, and go right to work. I understand it—they came to Yellowstone to fish, their time is limited, they’re going to fish. But the river flows cold, the fish largely inactive. Yes, the occasional trout will be caught, but what happens all too often is that these fishermen freeze out or tire out by the time the activity really begins. So at the most propitious time to fish, they’re pretty much done. Guard against this, if your goal is to have the best fishing possible.
It wasn’t until 3:23 p.m. that I saw my first rise. Others followed quickly. As I shouldered my vest and grabbed my rod, a couple Pale Morning Duns flew overhead. For the next hour and a half, I fished constantly to rising trout. By then my hands were frozen out, barely functioning to tie on a fly or dry one off. Fish continued to rise as I de-rigged and headed home to the warmth of the wood stove.
In the evening, I heard from friends that fished elsewhere on the river. The hatch of Pale Morning Duns where they were didn’t begin in earnest until 5:00 p.m., and they fished until 7:00 p.m. I’m not sure whether they quit because they’d caught enough, were tired out, frozen out, or whether the hatch simply ended. In any event, it was the knowledge of knowing how these shocks to the system play out that kept them on the water well past when most anglers have already thrown in the towel.
That’s knowledge worth having, and worth heeding.