Back in January of 1974 I realized a life-long dream when I moved to Montana. "Back in the day" living in Montana was an outdoorsman's idea of heaven. My wife was willing to move there, and I had a job which assured that I could actually stay. Soon I was living the dream.
That first winter in Montana was a steep learning curve. I had never done lots of fishing with big nymphs and much of the winter fly fishing that was taking place in those days was begin done with big nymphs. Gradually I got the hang of slinging big weighted nymphs and bouncing them along the bottom, but I really was hoping to find some other options. One day when I was standing in Dan Bailey's Fly Shop another angler came in and asked Dan if he had any snow flies. Dan pointed to a box of small black dry flies and the angler picked out a half dozen or so. After he left the store I asked Dan where a person would use such flies during the winter. When he told me that they were used on the Yellowstone I was instantly interested.
It turns out that snow flies are really just midges. Midges are common on the Yellowstone every month of the year, but during the winter months they are particularly noticeable because they are the only dry flies available at this time of the year. On almost any day when the temperatures are above freezing it possible to find midges hatching on the Yellowstone, and when the temperatures approach 40 degrees the hatch can be quite intense. The results can be excellent dry fly fishing in the middle of a Montana winter.
When I started to fish snow flies I soon discovered that the best fishing on the Yellowstone is found in the big foam slicks that form in back eddies and along the rip-rap placed along the banks for flood protection. Large pockets of floating foam slowly spin around and around like a big lazy Susan and the midge pupa and the hatching adults become trapped in the foam. The foam provides cover and trout and Rocky Mountain Whitefish will collect under the foam and feed on the pupa and the trapped adults.
The other place where trout gather to feed on snow flies is on the big pools and flats. This type of fishing is more difficult since normally the trout are cruising and the angler needs to stalk each individual fish. In the winter the water is crystal clear and the fish can be especially spooky.
As the winter begins to wane and the days become longer and the water gets warmer it's possible to encounter blanket hatches and then the trout will often collect in riffle corners where the hatching midges may congregate. The water is often shallow but when the flies are hatching the fish will move in to feed on the feast. It provides some fantastic fishing.
Snow flies are not just a Yellowstone phenomenon and winter hatching midges are found on most trout streams. Fishing these hatches requires the angler to be prepared for winter fishing conditions. When I fish during the winter I dress in layers and, although I wear chest high waders, I generally do very little wading. When the fish are feeding in the foam slicks they are normally easily fished from shore, and when I stalk fish on the flats I stay close to the bank and rarely wade in over knee deep. During warmer periods it's possible to float and that allows the angler to cover more water.
One of the nicest things about fishing snow flies it that the best fishing occurs after the air and the water temperatures have warmed up. It's not necessary to get up at the crack of dawn and you will not need to stay out until the sun sets. In midwinter the best fishing only last for an hour or so and as you get closer to spring it may extend for three or four hours, but it's almost always after noon.
I usually fish a two fly combo – an adult midge dry fly and a pupa imitation on a dropper tied off from the bend of the hook. I have also found another method that sometimes produces good results, especially when the fish are feeding in the foam slicks. I have discovered that the better fish lurk just under the foam and rarely show but they are feeding on the drown adults and crippled emergers under the foam. To get these fish I like to use a lightly weighted soft hackle. I want a fly that will break the surface film and drift just below the foam. I fish with a clean leader and maintain a constant tension between my hand and the fly. I allow the fly to drift around under the foam and I keep my eye on where the leader enters the water. The takes can be subtle but on many occasions the fish take fairly aggressively. Some of the best fish that I have taken when fish the foam slicks have fallen for this method.
In recent years I have spent the winter months in southern Arizona and I have not fished snow flies in several years. If you spend your winters where the temperatures fall into the single digits and sunny winter days cause your casting arm to begin to twitch you might check out your local waters to see if you have snow flies on your local waters.