Summer Streamflow and Fishing Outlook

This post is about likely summer and early fall water and fishing conditions, based on current snowpack and current predictions for spring weather. Please click the “Season Outlooks, Weather, and Water Conditions Updates” link in the Topic menu to view previous updates to learn how weather and water have tracked since mid-February. From now on I will be posting updates about once a week until the end of the spring runoff.

If you are unfamiliar with how streamflows work in the Rockies, here’s a quick rundown. To a large degree, streamflows are based on winter snowpack in the mountains and how this snow melts (when it starts and how fast it runs downhill). Summer rains have only minor effects and mostly impact day-to-day clarity rather than overall flow. Only from about the beginning of September onward are rain events likely to dramatically increase flow. Before this, the rivers simply have enough snowmelt in them and are running high enough that rain barely causes most streamflows to tick upward except on small rivers prone to thunderstorms, like Soda Butte Creek. In sum, snowpack is vital for determining the duration of spring runoff and the overall summer streamflows and water temperatures. Generally speaking, all rivers save those immediately downstream of large dams (such as the Missouri in its chain of lakes and the Madison below Ennis Lake) endure a spring runoff period of four to eight weeks of high and unfishable water levels, with the overall length and severity of the runoff depending on the body of water in question, the amount of snow in the hills, and when this snow starts melting. Therefore, knowledge of the amount of snow in the mountains and the way we expect this snow to melt is critically important for trip planning and predicting what we expect the summer and early fall fishing to be like. This crystal ball gets clearer the later into the spring we get.

We’re getting to crunch time now. The snow has basically stopped accumulating and we therefore have a much better idea of what we’re working with in terms of water for the 2017 season. In addition, it is likely that the spring runoff will begin within the next three weeks.

The first half of April was near-normal. Actually there were wild swings from warm and dry to cold and wet, but they average out to near-normal. In response, snowpack numbers have changed only slightly since the last update. We’re looking at snowpack ranging from 89% of normal to 135% of normal in our operations area, with the most important drainage–the Yellowstone basin in NW Wyoming and Yellowstone Park–at 135% of normal. Generally speaking, if you go northwest of our shop into the Missouri River basin, you find conditions near-normal to slightly dry. Go south and southeast into the basins of tributaries of the Yellowstone and you find drastically above normal snowpack.

Compared to this point in 2016 and 2015, which both saw dramatic snowmelt in early April, we have more snow in all river basins this year, and drastically more in most. At this point in 2016 (which saw better snowpack than 2015), the Yellowstone basin was at 84% of normal. So we’re currently more than 50 percentage points higher this year. The Yellowstone has the largest difference between this year and last, but most other basins are 10-30 points higher, as well.

We are now late enough into the spring that we can start guessing when the spring runoff will begin. We’ve already had surges of medium-elevation snowmelt, and the low elevation snow is effectively gone. The medium-elevation melt muddies things for a few days and has started the rivers in a general upward slope towards runoff, but except for a day or two after warm, sunny days, the rivers are still clear and fishable. In fact fishing has generally been very good as of late. The high-elevation snowmelt is what really blows things out for a few weeks. The timing of the beginning of runoff is a big factor in determining when rivers drop into shape again in June or early July.

The next week or so is forecast to be cool or seasonal in Gardiner, so there’s no chance the full runoff will begin during this time. Things get hazier thereafter. Right now the NOAA 6-10 and 8-14 day outlooks suggest warm weather during the latter part of April for us, with the potential for wet weather particularly in the last few days of the month. If this happens, there’s a good chance the spring runoff will begin in the last few days of April. On the other hand, the week 3-4 outlooks, which are much vaguer for obvious reasons, are now suggesting normal to cool weather for the last couple days of April and the first 10 days of May. If this actually happens, the runoff will stall and we may have something of a “double dip” start to runoff, a surge of high water that blows things out for a week or so followed by a week or two of great fishing before the runoff returns in earnest. It’s weather forecasts like this one that explain why I will be updating this forecast every week from now on, rather than biweekly as I do earlier in the winter…

So what’s all of this mean for summer fishing???

Here it is in a nutshell…

We anticipate above normal streamflows in the Yellowstone drainage throughout the summer season, particularly within Yellowstone Park and the upper end of Paradise Valley. Above normal streamflow is also likely in the Madison drainage, particularly within Yellowstone Park. Streamflows in the Missouri River should be near-normal, with below normal snowpack in the Missouri basin itself offset by above normal snowpack in the basins of its headwaters (except the Gallatin).

The precise course of the runoff depends on how we enter it. If we enter it early –in the last few days of April– and the runoff does not pause in early-mid May, we will have a near-normal end date for runoff on all waters and near-normal water conditions through the summer. If runoff either starts late or starts early but pauses, we will have a delayed end to runoff and high streamflows through the summer. We WILL NOT have substantially below normal streamflows on any waters in our operations area UNLESS the current weather outlooks are completely wrong. We’ll know for sure within two weeks. Overall, we hope to see a normal to late start to runoff, or the “double dip” mentioned above, because we’d rather have a slightly delayed clearing date for rivers that get muddy during the runoff (most of them) and higher flows through the summer than any other option, as this keeps the fish healthier, happier, and stupider.

Here are predicted clearing dates for the important waters in our operations area, as well as some general fishing notes. I have included a lot more info in this update, particularly for Yellowstone Basin fisheries within and just outside Yellowstone Park.

The Yellowstone River Outside YNP: The Yellowstone River may enter runoff in the last few days of April. If it does, our Mother’s Day Caddis hatch fishing will either be nonexistent or depend on a pause in the runoff around May 10. If we have a double-dip, drop everything and get here and fish, because the fishing is almost always spectacular during such pauses in the runoff. Once it enters runoff for good, the Yellowstone should drop into fishable shape again sometime in the first week of July. It’ll be July 1 if we have an early start to the runoff and no “double-dip,” more like July 7 if we have a normal start to runoff or a double-dip. We expect normal to above normal flows throughout the season, particularly from Livingston upstream, where flows are determined primarily by the snowpack within Yellowstone Park. East of Livingston, where snowpack is lower and irrigation demands greater, near-normal flows are more likely.

The Yellowstone Inside YNP: Generally similar to the Yellowstone outside the park, though the Grand Canyon should be fishable with nymphs and streamers by June 25 at the absolute latest. It will still be very high, however. The Black Canyon’s Salmonfly hatch will continue in spotty fashion at least through July 25 provided runoff holds off until April 25 and I would not be surprised to find the fish willing to eat a Salmonfly or two near cold tributaries until August 1. The Yellowstone between Yellowstone Lake and Sulphur Cauldron should offer better fishing this season than any year since the late 1990s. The lake trout populations are down, cutthroat numbers in the lake are rebounding in response, we’ve seen much stronger cutthroat numbers even during the past couple drought years than any other year since the late 90s, and flows from Yellowstone Lake will be higher than any other stretch of water in our entire operations area, which will push the cutthroats towards the banks where they will be easier to find. We WILL guide here this season, for the first time in more than a decade.

The Lamar Drainage: Slough Creek should become fishable in the first week of July, the Lamar and Soda Butte around July 7 to 10. We expect excellent water conditions on these streams this year, with some relief from the low water, crowded conditions, and overstressed fish of the past two August/September periods. I predict the most consistent (though not necessarily “best”) fishing on Slough Creek will occur in the second half of July, and on the Lamar and Soda Butte during the last ten days of July and first ten days of August. Slough Creek is sometimes fishable right at the beginning of the park season, for a few days, before the onset of heavy runoff. This is very unlikely this year due to the warm snowpack and likelihood of a heavy and early runoff.

The Firehole, Gibbon, and Madison: The Firehole will be fishable on the park opener (May 27), though likely still high and tea-stained. It will be the only river that will fish well on this date except POSSIBLY the Gardner, if the weather is cool. The Madison will come into shape around June 1, possibly as late as June 5, and the Gibbon below Norris will drop into shape around June 5. The Gibbon above Norris will not be ready before June 10 and will be much better after the 20th. Good fishing on the Firehole will continue until June 20 and will become day-to-day between June 20 and July 1, with cool temps necessary during this last ten days for acceptable fishing. July 4 through Labor Day will see water temps too high for the Firehole to be fishable. The Madison and Gibbon below Norris Geyser Basin should fish well through July 1 and in the mornings through at least July 4, though cool weather will extend the general fishing through July 4 and the morning fishing through July 15. They will be too warm from July 15 through Labor Day in a general sense, though the Madison from the Barns Pools down to Hebgen Lake can be worth it in the mornings after August 20 provided nights are cool.

Gardner River and Tributaries: The mainstem Gardner downstream of Boiling River is always fishable from the beginning of the park season for fit anglers willing to handle very rough and physical walking and wading FOLLOWING A DAY OR TWO OF COOL, DRY WEATHER, WHILE BEING TOO HIGH AND DIRTY AT OTHER TIMES. This pattern will continue through June 20-25 this year, with the river fishable almost every day thereafter. The river will be fishable on a day-to-day basis from Osprey Falls to Boiling River after June 20 and for good after July 1. Above Osprey Falls, consistent fishing will not begin until after July 4 and maybe as late as July 10. The tributary creeks will come into play the last ten days of June or possibly as late as July 4. The lakes will be ready by the opener, though Fawn will be difficult to access until June 20 due to the river and stream crossings required. Joffe Lake MAY be the only body of water across the north end of the park to be easily accessible, open to fishing, and fishing well on the opener. It depends on the day-to-day weather.

Small Streams: With the exception of those in the Firehole drainage (ready in mid-June and good by July 1) and those in the Gardner Basin (see notes in the Gardner entry above), most small streams will not be fishable before mid-July and will be best in August and early September. This will be a good late summer for the small streams, which is when we most love to fish them.

Lakes in Yellowstone Park: Yellowstone Lake will be best before July 1 and should be fishable from the opener. Lewis Lake will ice-out by the end of the first week of June and will fish best in the two weeks thereafter. Shoshone Lake will ice-out at the same time but will be difficult to access accept by boat until late June, due to snow on the trails. Smaller lakes except Blacktail (which opens July 3) will be ready to fish and accessible by June 10 and will fish best from this point through early July. See notes in the Gardner River entry for lakes in its drainage.

The Lower Madison below Ennis Lake: Recent reductions in the snowpack of the upper Madison River Basin outside YNP mean that the lower Madison below Ennis Lake will see near-normal water conditions this year, maybe just SLIGHTLY high. The river is floatable now and should remain so through June 20 at least. Here’s hoping for cool weather in late June to keep this water cool enough to fish well until the Yellowstone clears. Otherwise, we might have a week or ten days when the Yellowstone is still too high and dirty and this water is too warm, and therefore not have anywhere to float…

The Missouri: Recent reductions in snowpack in most of its tributary basins as well as the mainstem Missouri basin itself mean that near-normal water conditions are likely. This is a bummer as this water could use a good flush to reduce weed growth. We still expect good fishing on my (Walter’s) jet boat guide trips here from late this month through early June, but this water will likely be low and full of weeds and therefore not worth the trip from late July through September, as has been the case the past two seasons. I have four guided trips here the week beginning April 23, though a lot of prime dates are still available in May and early June.

Private Lakes: The lakes (particularly the Story Lakes) are already in shape and fishing well. They should see normal conditions this year, with Story and Merrell fishing well into late June and Burns fishing through July.

Paradise Valley Spring Creeks: The creeks are not impacted by runoff. Fishing is best before mid-May and again from June 20 through July, then gets steadily better once more after September 15.

Overall, we expect solid average to somewhat above average streamflows this season, based on current snowpack numbers and predicted forecasts/outlooks through April. We will have higher water than 2016, 2015, 2013, and 2012, with lower water than 2014 and 2011. For the moment, we anticipate conditions comparable to 2010.

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