As readers should know from previous posts on the subject, winter and early spring snowfall and how this snow melts from April into June are the most important drivers of summer water conditions in our area. I make reports on the progress of the snowpack through the end of the spring runoff in late June or early July, with the reports getting more detailed as the season progresses and we start to get a firm handle on what to expect.
In general, we like to see snowpack between 100% and 120% of normal, with 105-110% absolutely ideal. With snowpack at this level, waters drop out of the spring runoff at about their normal time (between early June and July 10 depending on the water in question), but flows remain high enough and therefore cool enough through late July and early August for the fish to remain aggressive and happy. With higher snowpack, the fishing once the water clears is great, but we start late and miss much of the prime summer tourist season. In 2011, we weren’t able to begin floating the Yellowstone until July 28, for example. If snowpack is dramatically low, we get an early start and have good fishing until about mid-July, but mid-July through late August can be tough fishing and we may need to start and end early.
As of right now, here’s where we’re at. Our approximate operations area is circled in red. I have also added in the drainage basins for the Upper Yellowstone system in Wyoming and Yellowstone Park (including the Lamar and Gardner Rivers) and the Madison/Gallatin basin in Yellowstone Park, including the Firehole and Gibbon Rivers.
As you can see, things are looking good right now in most of our operations area, with drainage basins in our operations area ranging from 92% to 127% of normal. By far the most important basins for our operations are the Upper Yellowstone basins in Montana and Wyoming/YNP. These are at 113% and 111%, respectively. The low spots are the Madison in Montana and Madison/Gallatin in YNP.
Because the winter has been warm and we’ve got warm, rainy weather in the forecast for the next week, I expect these numbers to all drop over the next week. Beyond that, long range NOAA outlooks for the 6-10 day forecast period suggest above normal precip and below normal temperatures (aka good chance it’ll be snowy), while the 8-14 day outlook suggests an equal chance of above, below, and normal temperatures with a greater chance of above normal precip. Very long range outlooks extending through the spring suggest greater likelihood of above normal temperatures as well as above normal precip.
We still have a good six weeks of “snowpack building time,” and the above outlooks do not look likely to drastically change our overall snowpack numbers, though I do expect them to decline a few points. We’ve had a warm winter, so the medium-elevation snow will start melting as soon as it gets rained on.
In regards to most of our operations area, in particular the Yellowstone Basin inside and outside Yellowstone Park, I should note that assuming the “average to somewhat high” snowpack numbers we’re seeing so far continue, we should have good to excellent water conditions for this summer, the fourth year in a row things have run average to a bit above. This will be the first time in my career (20 seasons counting 2020) that we’ve had this many years of solid water conditions in a row. We had great fishing and healthy fish last year, with the Yellowstone seeing probably its strongest average size range in at least ten years. Will this trend continue in 2020? I wouldn’t bet against it…
The Madison/Gallatin Basin inside Yellowstone Park is a different matter. It would not surprise me to see this snowpack drop to 85% of normal by the end of next week, with the bulk of the drop in the lower-elevation Madison portion of this shared basin. The storms have generally been going either just north of the park or just south of it, leaving the Madison Basin inside the park just off the storm track. This below average snowpack could become a problem if the forecast warmer than average weather for the next three months materializes. The Madison outside the park should be fine, particularly upstream of Ennis Lake, but the Firehole, Gibbon, and Madison inside the park might suffer due to low/warm water this year as they have not since 2016. The Firehole in particular may wind up getting too warm by around June 20, whereas it has fished well through June the past few years. We’ll have to wait and see on this. If you’re a Firehole-lover, I suggest doing some snow dances.