Season Outlook, Streamflow, and Fishing Forecast Update

This post is about likely summer and early fall water and fishing conditions, based on current snowpack and current predictions for late winter and early 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, I’ll be posting updates on about a biweekly basis until about the middle of April, then weekly updates thereafter.

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 six 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.

It is now getting late enough in the winter for us to begin having a pretty good idea what we’re looking at for summer and early fall water conditions, so this update and those that follow should prove very important for trip planning.

Since the previous update, we had a few days of relatively warm and extremely snowy weather in the mountains that pushed snowpack to its highest levels as a percentage of average so far this winter, but this came to a crashing halt around March 12, when extremely warm and generally dry weather rolled in from the SW United States. A few days ago, Bozeman had its record high for the date, over 70 degrees. As you can imagine from that number, all low-elevation (below about 6000 feet) snow is essentially gone, all rivers are ice-free, and there’s a fair amount of mud in many rivers. Once this mud clears, the spring “pre-runoff” fishing will be red hot on all rivers that are open (basically everything except Yellowstone Park). The warm weather is on its way out now and the high-elevation snow (about about 7500 feet) is back on the rise. The long-range outlooks extending through April call for normal to below normal temperatures and normal to above normal moisture. With normal temperatures, snowpack will continue to build except below 7000 feet through at least mid-April, early May at over 9000 feet. This warm weather has had a profound effect on the structure of the snowpack itself, however. During the warm spell, nights barely touched freezing even at the highest elevations. This consolidated and dramatically warmed the snow and will make it less resistant to the first major warmup (50s-60s at high elevation). In scientific terms, the snowpack is now “isothermal” or close to it except at the highest elevations, meaning it is near the freezing point, wet, and the same temperature from the surface all the way to the ground. Isothermal snow is primed for runoff. We now expect a very HEAVY and sudden onset to the spring melt, probably in the last few days of April or the first few days of May. Once it blows, it’ll blow hard.

Despite the warmup, snowpack actually increased in some basins since the last update, largely due to the very wet system that hit us between about March 6 and March 10. Only low-elevation basins to the NW of Yellowstone Park saw substantial decreases. Snowpack now ranges from 94% to 144% of normal in the Parks’ Fly Shop operations area, with the three highest numbers in the most important basins for our range. In Yellowstone Park and far northern Wyoming, the most important water source for the Yellowstone River, Lamar Drainage, and Gardner River, snowpack is at 144% (up five points). In the Madison-Gallatin basin inside YNP, it’s at 126% (down a point). In the Yellowstone drainage north of Yellowstone Park, it’s at 128% (up three points). At 94% to 109%, basins west and northwest of Yellowstone Park are all down several points. It’s important to note that the rivers in these basins (Madison, Gallatin, and upper Missouri) all receive water from the Madison-Gallatin drainage inside the park as well. Since this drainage is so high, it will make up some or all of the difference.

Compared to last season, snowpack in the three most important basins in our operations area (Yellowstone in YNP and Wyoming, Madison-Gallatin, and Yellowstone in MT) range from about 30 points to about 55 points higher than they were last year. Generally speaking, the differences between 2017 and 2015 are even more stark. In addition, April was exceptionally warm in both 2015 and 2016, which does not look to be the case this year. We saw catastrophic declines in snowpack in April in both of the last two years that just don’t seem likely this year. I would not be at all surprised to see numbers on April 20 that are 75 points higher this year than last year or the year before. Looking even further back, conditions in the Yellowstone basins and the Madison-Gallatin basin are roughly comparable to where we were at on this date in 2014, 2011, and 2008, all years that saw a heavy and long-lasting spring melt followed by excellent fishing and great water conditions throughout the summer once the rivers finally cleared.

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

Here it is in a nutshell…

We anticipate above average overall streamflow during the peak summer and early fall season on all waters in our operations area with the possib;e exception of the lower Gallatin River, coupled with late clearing from the spring melt on all waters that are subject to muddy water due to the melt. This basically means everything besides the Lower Madison and Missouri Rivers, the Paradise Vally spring creeks, and private lakes. Everything else will clear late and run normal to high through the summer, with cooler than normal water temperatures and less-spooky fish.

In general, the current snowpack that’s on the ground as well as what’s predicted for the remainder of late winter and early spring lead to excellent and consistent fishing ONCE THE WATER IN QUESTION DROPS OUT OF RUNOFF. This is a key distinction that visitors who have fished this area in the drought years this century (2001-2007, 2012, 2013, 2015, 2016) need to bear in mind. We have recieved many calls asking about floating the Yellowstone between June 20 and the end of the month. This period was epic the last two seasons, but it will almost certainly be completely impossible this year. A good rule of thumb is to shift your fishing dates back by two weeks if your trip falls prior to July 15 if you want comparable conditions to what we had in any of the drought years mentioned above. If you’ve fished with us from July-September in 2010 or 2014, these years are good analogs for the water conditions we expect.

Here are predicted clearing dates for the important waters in our operations area, as well as some general fishing notes.

The Yellowstone River Outside YNP: Will clear from runoff late, unless runoff starts two or more weeks early (late April). It will also clear at a higher-than-normal level. Streamflows should be excellent from July 10 or so through the remainder of the season, but float trips will be chancy at best from the onset of the runoff until AT LEAST July 1. It may or may not be clear by July 4. In 2014, the most comparable year to this one, we ran our first float trip on about July 8, and that sounds pretty likely this year too. We will not be accepting Yellowstone River float trip reservations for trips between May 1 and July 14 until we have a better handle on the precise timing of runoff unless anglers are willing to float the Madison or do some other type of trip (walk, private lake, or jet boat) instead if the Yellowstone is unfishable. The onset of runoff will be a huge determining factor here. If it starts in late April, we’ll see a near-normal clearing date. If it starts as normal around May 5-10, we’ll see a slightly late opening (around July 10). With the shot of warm weather we had earlier this month, it now seems very unlikely we’re in for an exceptionally late start, so dates after July 15 are now definitely safe.

The Yellowstone Inside YNP: May be fishable as early as mid-June in the Grand Canyon, but early-mid July is a safer bet in the Black Canyon.

The Lamar Drainage: Cannot be counted on before mid-July, though Slough will probably be ready July 10. Good fishing should abound thereafter, with the fish seeing some relief from the extreme low flows of the past two summers.

The Firehole, Gibbon, and Madison: Should have extended seasons (through June even for the Firehole) due to higher, cooler water. These will be our most important and best fisheries through most of June. TThe Gibbon and Madison may not be fishable until June 5 or even a few days later for the Gibbon, while the Firehole SHOULD be fishable when the park opens on May 27, though if there’s a lot of snow remaining in its basin on the opener and it decides to get warm and dump rain, that could be a problem even on the Firehole for a few days. On the flipside, it’s now at least possible the Madison and Gibbon will remain fishable through July.

Private Lakes: Those with natural inflow (the Story Lakes in particular) should see extended seasons. The others will depend on short-term weather. These lakes should not be impacted by runoff. The recent low-elevation warmth means that upper Story Lake is good to go; the snowdrift that blocks access in cold springs should be about gone now.

The Lower Madison: Since the upper Madison system in YNP has excellent snowpack, the lower Madison should run high and cool for longer than usual. This is a good thing, as this will be our float river through June this year. The upper Madison above Ennis Lake may be muddy through most of June.

The Missouri: Should see normal to slightly above normal flows. We were hoping for a later melt in the lower basins impacting this water, since it has been three seasons now since this water has had a good flush and it actually fishes very well when the water’s high, since the dams clear out the sediment and high flows concentrate the fish. Overall, flows and fishing should be slightly better April-June this year than last.

Let me reiterate: we expect excellent to epic mid-late summer and early fall conditions in the Yellowstone drainage (including its tributaries like the Lamar) and early summer conditions in the Firehole, Madison, Gibbon, and Missouri systems. Early summer in the Yellowstone and Lamar drainages (before at least the beginning of July and probably a week later) will be far more limited. Since our busy season and usual better fishing is from the 4th of July through September, this is what we want to see.

3 comments on “Season Outlook, Streamflow, and Fishing Forecast Update

  1. Thank you for the nice update. I find the information you presented to be very helpful. I appreciate you taking the time to post the information.

  2. Very impressive update; thanks very much for taking the time to provide this information.

  3. Thanks for a great summary. We are excited about another year fishing the Yellowstone.

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