Runoff Report and Summer/Fall Streamflow Forecast and Fishing Outlook for Late May, 2021

Posted on May 31st, 2021 in Area Fishing News, Season Forecasts, Weather & Water Conditions


Winter snowpack and how this snow melts from April through June are the primary drivers of summer water conditions: whether the water’s high or low, whether it’s warm or cold, etc. This in turn drives the fishing. In general, we like to see slightly above-normal snowpack since this leads to cool water and aggressive fish.

The lower the snowpack and hotter and drier the summer weather, the more likely we will have tough or limited fishing on late summer afternoons due to warm water. In exceptionally hot/dry years, we may even have stream closures in core watersheds in our operations area. Some watersheds are now always closed from 2:00PM to midnight in late July and August, though none of these are important fisheries at this time.

Winter and Early Spring Weather Summary

Winter started with a bang in early October, with over a foot of snow and below-zero temperatures even in Livingston. Things then got dry by early November and stayed that way through January. The early part of winter was so dry that Bridger Bowl Ski Area had to delay its opening until almost Christmas.

February really saved our bacon. The whole month was very cold and very wet. In fact the ski area set its record for February snowfall. This heavy snowfall propelled Yellowstone and Montana snowpack to above normal levels in most river drainages by mid-February. Those that didn’t jump above average climbed over the 95th percentile, close enough.

March returned to slightly warm and slightly dry conditions for most of the month, with a few cold and wet outbreaks. Snowpack increased in a general sense, but declined against average.

April turned out to be highly variable, despite a forecast that predicted warm and dry. We’d go from a couple days of light snowfall that mostly melted by noon (here in the low country) to bright sun and 65 degrees a day later. The last few days of April were exceptionally warm, with temperatures in Livingston reaching the mid-80s on the 30th. This prompted an early start to the snowmelt.

May was highly variable, with weather yo-yoing from hot and dry to cold and wet. We had accumulating snowfall that stuck around for a couple days here in Livingston as recently as May 20. June 5 it is forecast to hit 90 degrees. That’s how the spring has gone. On balance, May was probably a bit drier than normal.

Current Yellowstone and Montana Snowpack and Runoff Update

Current snowpack ranges from 38% to 129% of normal in the Yellowstone Country Fly Fishing areas of operation. Runoff is well underway everywhere, which is a big reason why these numbers are so variable. The other big factor is a heavy winter storm that mostly impacted central and northern Montana ten days ago. Basically, high mountains and especially high mountains north of here still have good snowpack. Otherwise, the snow’s almost gone.

Snowpack is 75% of normal in the  Upper Yellowstone Basin in Wyoming, basically meaning the Yellowstone River and all its tributaries upstream of Gardiner, Montana. This comprises all the core summer water within Yellowstone Park. The Upper Yellowstone Basin in Montana is at 77% of normal. This includes the Yellowstone Basin (including the Wyoming water) downstream to the Clark Fork confluence near Billings, Montana, at the eastern edge of YCFF’s operations area and beyond the Parks Fly Shop operations area.

Besides the above basins, which are the most important river drainages for both businesses, snowpack ranges from 38% of normal in the Madison-Gallatin Basin in YNP to  129% of normal in the Smith-Judith-Musselshell Basin, which barely touches on our operations area.

In general, snowpack is low to very low across the important drainages in our operations area. With above normal temperatures in the forecast, things will not improve.

General Expectations for Summer

Based on current Montana snowpack and predictions for June we expect the following for the core June-early September season. Conditions after mid-September depend on fall rain and snowfall:

  • A short runoff cycle that will end in all but the highest drainages by June 20.
  • Below-normal stream levels from this writing onward.
  • Above-normal water temperatures in all river basins between July 10 and August 15-20
  • More 2:00PM fishing closures than usual between the above dates.
  • Potential for poor fishing conditions after 2:00-3:00 during hot spells on many fisheries that do not meet closure criteria (note: Montana closes trout fisheries from 2:00-midnight when they touch 73 degrees three consecutive days to avoid stressing trout; above 70 is poor fishing anyway)
  • Potential for round-the-clock fishing closures in a few low-elevation fisheries (note: these are unimportant fisheries to most anglers in midsummer)
  • Spookier than normal fish in late July, August, and September
  • More fires than usual from late July through September

Water-Specific Predictions

This is the meat and potatoes for most visiting anglers. Here’s when we expect various important fisheries to blow out with runoff, clear from runoff, and how we expect they’ll fish through the summer. Within each jurisdiction, waters are discussed in approximate order of when they’ll leave spring runoff.

Montana Fisheries

Private Lakes: The private lakes are now enjoying their best fishing of the year. Given the hot weather forecast for the upcoming week, we anticipate some lakes will begin slowing down by mid-June this year. All lakes will be poor from the beginning of July through mid-September.

Missouri River – Land of Giants: Very low flows have led to crowded and so-so fishing on the Missouri so far this season. Weeds will be heavy in July and August due to the low flows, which will probably prevent us from fishing here July-September.

Area Reservoirs: Like the private lakes, the reservoirs are at their best right now and will likely begin falling off into summer doldrums with the upcoming heat wave. High-elevations reservoirs like Hyalite near Bozeman and Hebgen near West Yellowstone are a very different matter and should be fine except on hot/bright/windy afternoons in July and early August.

Madison River (Lower): The Lower Madison is at or near its best fishing of the year, though it’s very low. Caddis pupae, Yellow Sallies, and crayfish are working, and PMD might also be on tap. Forecast high temps will do this water no favors, though it probably won’t be too warm to fish before about June 20-25. The Lower Madison is always closed to fishing from 2:00PM until midnight from July 15-August 15. In reality it ought to be June 25 through Labor Day this year.

Jefferson River: The “Jeff” is now blown with spring runoff until about June 10. High air temps and low flows do this low-elevation river no favors. We might not have ANY fishable window between the end of the runoff and the onset of high water temps. Expect 24-hour closures here in late July and August, with 2pm to midnight closures in early July.

Boulder River: The Boulder has just gone into its heavy runoff, but it will drop quickly too. We expect marginal fishability by June 15. It’s very likely going to be an exceptionally short float season on the Boulder this year, with flows falling under the 500cfs threshold by July 15 to 20 at the latest. Expect low flows and stressed fish in late July and August, so no wade-fishing downstream of Natural Bridge in late summer, either. 2:00PM closures are possible in August from Natural Bridge to the Yellowstone.

Stillwater River: The heavy runoff has now hit on the Stillwater. Points upstream from the Rosebud confluence should come into shape June 15-20. Downstream, around July 1. Prime floating flows will be from June 20-25 through early August depending on the stretch. The upper Stillwater above the Rosebud will get too low by August 1. The lower Stillwater will likely get too low to float sometime between August 20 and Labor Day unless good late summer moisture occurs to keep things up. High water temperatures below the Rosebud confluence are likely in early August, with 2:00 closures possible but unlikely. More likely, you’ll just want to launch early and take off by 3:00 during hot spells.

Yellowstone River: The Yellowstone will experience maximum runoff around June 4 this year, with flows forecast to peak around 14,000cfs at the Corwin Springs gauge.. This is 6,000cfs below normal. Because of the low peak, expect fishable flows by June 20 at the absolute latest, with June 15 very possible. The most consistent fishing will range from June 25 to early August depending on the section and the weather. Late July and August will see water temperatures over 70 degrees on many hot afternoons. 2:00 closures are possible on the entire Yellowstone outside YNP but are most likely east of Livingston. Regardless of any mandatory closures, lots of days will demand “early-on, early-off” for good fishing, especially the week either side of the beginning of August when maximum sun/heat combine with lower flows. We expect many of our guided trips to meet by 6:30AM and be off the water around 3:00 during this period regardless of legalities. Mandatory 24-hour closures are unlikely anywhere on the Yellowstone, but are possible east of Livingston and especially east of Big Timber.

The Salmonfly hatch on the Yellowstone will almost certainly be fishable this year, though it will probably be of short duration. Look for the hatch from June 20 through July 4 depending on June weather and the specific stretch of river.

Most Small Streams: Except for a couple low-elevation odds and ends that fish well from mid-June until early July, like the Musselshell River and upper Smith River, most small streams will begin coming into shape in the first week of July and be best between mid-July and Labor Day. Most run ice-cold, which makes them excellent bets in late July and August on afternoons when big rivers may be too warm.

Yellowstone Park Fisheries

The Yellowstone Park fishing season opened May 29. Most “westside” fisheries are clear and fishable already, with the Firehole already probably at its best fishing level and temperature of the year. Crowds have been overwhelming, though. The rest of the park will become fishable between June 10 and July 1, depending on the water. The upper Yellowstone and a few other odds and ends do not open until July 15. Check regs to be sure!

Please note that fall fishing is really not discussed here. Most or all of the larger rivers in YNP become good again after September 1 when cooler nights allow water temps to drop.

Firehole River: The Firehole is low, clear, warm, and crowded. The extreme lower Firehole has already hit 70 degree water temps right above its confluence with the Gibbon, though most of the river is still in the high 50s or low 60s. The best fishing of the “early” season is already occurring on the Firehole. It will get too low and warm for good afternoon fishing by June 10 and maybe June 5. It will get too low and warm period around June 20 absent cool and wet weather. Yellowstone Country Fly Fishing does not expect to run ANY trips on the Firehole this spring due to the short cool-water window. If 24-hour closures are not instituted on the Firehole in July and August due to high water temps, shame on Yellowstone Park.

Madison River in YNP: The Maddy in YNP is clear and fishable and will be best before June 20. It will be too warm on bright afternoons thereafter and too warm period between July 1 and late August. Closures should but probably won’t be instituted from July 4 through August 15-20.

Gibbon River in YNP: The Lower Gibbon below Gibbon Meadows is low enough and clear enough now and will be best from June 1 through June 15. It will gradually get too warm thereafter and be too warm in July and August. From Norris Geyser Basin through Gibbon Meadows is in shape now and will be best from June 10 to June 20 and too warm between July 4 and Labor Day. From Virginia Cascade to Norris will drop into shape around June 10 and be best in July and early August. Upstream of Virginia Cascades is still undergoing grayling and westslope cutthroat restoration so is not recommended this year. 2:00 closures are likely and warranted below Norris Geyser Basin in late July and August.

YNP Lakes: All Yellowstone Park lakes that are open are accessible and fishable. Blacktail doesn’t open until July 1 and will likely already be too warm. Yellowstone Lake will be best before June 20. Cascade and Grebe will be best June 10 through early July.

YNP Central Plateau Streams: Streams like Nez Perce will drop into shape around June 10 and be best in late June and July.

Gardner River: Given the warm weather forecast, we don’t anticipate any “runoff breaks” on the Gardner. That said, it’ll be nymphable for good below Boiling River around June 10 and good by June 15. Osprey Falls to Boiling River will be a week later due to colder water. Above Osprey Falls will come in June 20 to July 1 depending on section and will be best in July. Below Boiling River will be too warm in the afternoons and may see closures in late July and August. The park is often overzealous with lower Gardner closures and may shut things down from Osprey Falls on down if they institute any closures at all. Closures between Osprey and Boiling River are NEVER warranted since this water stays below 65 all summer long no matter the weather.

Yellowstone River: The Yellowstone River above the falls always opens July 15 and will be best for the first two weeks. From the falls to the Lamar (Grand Canyon) will begin coming into shape around June 10-15 and be best from the point it’s barely fishable until about July 20 and again after September 15. It will be cool enough all summer, but can see heavy pressure in easy-access areas in late July and August. In the Black Canyon from the Lamar to Gardiner, it will track similarly to the Yellowstone outside the park as described above, except the Salmonflies will be present primarily in the first half of July and there’s less likelihood it’ll get too warm after 2:00 on late summer afternoons. Closures are unlikely on the Yellowstone inside YNP, though if the park institutes any closures at all they tend to go hog-wild with them.

Lamar, Soda Butte, and Slough Creek: Rough stretches of Slough and the Lamar will start coming in around June 20. Meadow stretches will come in around June 25 to July 1. The fishing will be best in July and on August mornings, though fishing will be good on cloudy afternoons even through August. We anticipate OVERWHELMING crowds on roadside easy-access portions of these streams this year. We’re talking people every 25 yards. This is due to the pent-up demand from people who didn’t travel last year combined with people who still can’t travel to more exotic locations overseas as well as low water that concentrates people in the main channels rather than allowing them to spread out in side channels. Closures are possible but unlikely in late July and August, though as noted the park can go bananas when they do institute closures (most recently 2007).

Rough Small Streams: As usual, small streams draining areas other than the park’s central plateau are steeper and rougher than others. They will come in around July 1 and be best from July 10 through mid-August.