Winter Snowpack and Summer Streamflow and Fishing Forecast – Late March Update, by Walter

Most of the information I posted a month ago is still true. In short: we have had a very snowy winter and anticipate a long-lasting and intense spring runoff, followed by higher-than-average midsummer through early fall streamflows. This makes for a tough June and probably first part of July if you like the Yellowstone and Lamar (as well as the Lamar’s tribs Slough and Soda Butte), but it makes for GREAT fishing once the water drops. Simply put, the higher the water remains through the summer, provided it’s clear, the better the fishing. The high flows make the fish more aggressive and keep the water cool, as well as keeping weed growth to a minimum. Win-win all around. We would much rather have fewer good fishing options in June and great fishing from sometime in the first half of July all the way through the rest of the core season than have great fishing in late June and stream closures in August…

For what it’s worth, the next update will appear mid-April.


Here are some more details:

Winter began in September and October, with bitter cold and snow that never melted. I was in Alaska from about September 15 through 25, and it was colder in Montana (and the fishing is also less-crowded in Montana, really). November was warm, December and early January were near-average in precip and above normal in temps. Mid-January through the first half of March were cold and exceptionally wet, so that’s what made our winter. Late March has alternated between warm and dry and cool and wet. April and May are supposed to see more of the same.

The cold and wet winter means that we now have drastically above normal snowpack in all basins within our operations area. Snowpack ranges from 121% of normal in the Madison-Gallatin drainage within Yellowstone Park to 156% of normal in the Yellowstone drainage in and above Yellowstone Park. Other drainages in our operations area are generally in the 130-odd percentage. These numbers are well above last year’s at this time except in the Madison-Gallatin drainage, which is about where it was at this point. Other areas are 20-40 points higher.

The above means that it is now certain we will have above-average winter snowpack and thus almost certainly will have a prolonged and heavy runoff. In fact, all snow depth monitoring stations are now reporting snow water above the average yearly maximum. In other words, even if it doesn’t snow another flake (it is supposed to snow for the next three days in the mountains), we will still wind up with above average snowfall. The only way this won’t translate into high streamflows this summer is if runoff begins catastrophically early with record warmth in late April. I do mean “catastrophically.” If it gets to 85 degrees for a few days around April 20, Livingston is going to wash away and wind up somewhere in North Dakota. This is highly unlikely, so don’t fret.

So what is likely? A late start to the season on runoff-impacted waters, with “how late” depending on when runoff starts. If runoff starts earlier than normal but a typical rise in flows, things might only be 2-3 days late. If things start at the normal time, typically the end of the first week in May, odds are summer fishing in places like the Lamar will be delayed a week or ten days. If it keeps snowing through early May and May sees a slow warmup that doesn’t get the runoff started until May 20 or so, we could be looking at sometime in the latter half of July for the Yellowstone and Lamar systems.


So what does all the above mean for specific fisheries? We can’t be sure until we see when runoff starts and how it progresses, but here are some prognostications. These will get more accurate and specific as spring progresses.

Yellowstone River: The Mother’s Day caddis may or may not happen in the first ten days of May. It depends on how the runoff progresses. The best scenario is for a solid mid-April warmup to blow out the last of the low-elevation snow, followed by a cooldown and then a slow rise into the 60s in early May. Runoff will probably hit in earnest sometime between May 5 and 15. We then expect the Yellowstone to be utterly blown out until at least July 1. After that, when it becomes fishable depends on how soon and how hard runoff hits. Right now we expect the Yellowstone to PROBABLY fall back into shape between July 5 and 15, hopefully around the 8th-10th. If the river drops into shape before the 10th, we should have Salmonfly hatch fishing outside the park. If it’s after the 15th, the hatch will probably be blown out for float trips. That said, the hatch will almost certainly continue through July 25 in the canyons in the park, and maybe into early August. Thus, there will be hike-in “big bug” fishing even if we don’t have any inside the park. Once the river drops into shape, we expect VERY GOOD TO EPIC fishing all summer. There’s just going to be too much cold water running downhill for a realistic chance of too-warm water this year. The dry fly fishing in July and August in particular should be very good, provided you’re up for chucking your flies into the bushes… Yankee Jim Canyon should become fishable sometime in the first half of August, if you like floating this water with Walter. Absent a record-dry summer, it should remain floatable through at least September 20. This means this will be another rare year which should see the opportunity to fish the fall BWO and Drake Mackeral hatches in the canyon (40-fish, one-angler half-day guide trips, all on dries, the last year this happened, FYI).

Lamar, Soda Butte, and Slough: Will probably fall into shape between July 7 and 15, though this could be delayed until the 20th or after if runoff is dramatically delayed. Green Drake hatches should be strong through early August, and this could be a year when there isn’t much of a late August/early September doldrums on these waters as there usually is. The real key for these waters is when runoff starts and how severe it is during the month of May. They always offer good fishing in the summer, since they’re up high and cold, it’s just a question of when it will start.

Firehole, Gibbon, and Madison in YNP these will be the big beneficiaries in the early season. The Firehole will be the star of the show through at least June 10. The Madison may or may not be fishable in the last few days of May (don’t count on it). I expect both the Madison and the Gibbon to fall gradually into play between the 5th and 15th of June. The Firehole will stay cool and good (they are one and the same on that river) through at least June 25, and probably July 1 at least in the mornings. Maybe even July 4-10 if June is cool. The Gibbon will be good until July 4 at least. The Madison will be about the same, and this is one of those years where if we have a cool summer it might only see a couple weeks of doldrums in late July and early August, wherein even the mornings might still fish.

Missouri River: Will be fishable all spring. They are already drawing down the reservoirs to keep flows reasonable in late May and early June. That said, late May and early June should be BIG. Expect flows in the 12,000 to 16,000cfs range. The river needs a good flush so we are glad of it. In regards to what this means for the fishing: book your trips now for late May and June. Do it now. I mean right now. Last year when flows were over 10,000 in the latter half of May and first week of June, Walter had his best guided trips ever on the Missouri. Fat silver rockets that were gorging on dislodged eggs and especially sowbugs. Fish under 16 inches were getting into the backing even though the clients were running 3X leaders. You just have to like nymphing, and often deep nymphing. The leaders we were running were 3 feet of 20lb bright orange Amnesia, seven feet of 2X, and a foot of 3X fluoro to the top fly (a sowbug, always), with up to four split shot.

Small Streams: Except for a couple meadow streams, especially those that run out of lakes in Yellowstone Park, these aren’t even going to be worth thinking about until June 20 or after. Except for the lake-fed creeks, which will be best in July, August and early September is certainly going to be the best time on these waters.

Small Lakes in YNP: Those that are legal to fish on the opener will still generally be snowbound and/or frozen. They will be reachable and open by June 15 and fish best for the month thereafter. Be prepared to hike in waders, because the trails will be marsh.

Spring Creeks and Private Lakes: Not impacted by runoff and as such very good choices this year (as well as any year) from basically right now through June or early July in the case of the lakes, and through July in the case of the creeks. Your prime PMD days in early July are already fully booked probably.

More details and specifics in later updates.

2 comments on “Winter Snowpack and Summer Streamflow and Fishing Forecast – Late March Update, by Walter

  1. It is reports like this that I consider Park’s to be the greatest fly shop in this or any other parallel universe. Every year, I look forward to these updates, and you guys never fail in getting me out west at the right time, with the right gear, every single year. It doesn’t matter if I’m fully geared out or not, I’ll be stopping by to get something, probably many things, necessary doesn’t matter. It’s the least I could do to repay you guys for YEARS of making my fishing life much better. Keep up the good work, and I’ll be seeing you in a few months.

    Many Thanks,

    Gary Long

    • Wow! Thanks for the kind words. The fishing will be good this summer… eventually. Unless something weird happens in the next three weeks, we will have a late start to the high summer fishing in the Yellowstone drainage.

      If you wanted to post some variant of your comment on Tripadvisor or as a Google review, we wouldn’t complain at all… 🙂

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