Daytime temperatures in the Yellowstone area range from 100 degrees Fahrenheit at the lowest elevations along the Missouri and Yellowstone Rivers on the hottest days in late July or early August down to perhaps thirty degrees below zero in January, even in the same low-elevation locations. Conditions can change in a manner of minutes; it's not unusual for late summer cold fronts to roll in, drop the temperature 30 degrees, and spit icy rain and hail following pleasant mornings with sunshine and temperatures in the 70s. Hypothermia is almost as big a risk in the summer as in the dead of winter, simply because people don't come prepared for changes in weather. This page is designed to ensure you bring the right clothing to be prepared for all eventualities. Odds are you won't need all the layers you bring on any one trip, but you're better off bringing items you don't need than leaving behind those you do.
In general, plan to bring layers. Temperatures almost always change by 20 degrees between early morning and midafternoon, and in early autumn they might change more like 40 degrees. Even in the summer, most people from warmer climates will want jackets first thing in the morning, particularly at high elevations in Yellowstone Park. Poly and other other breathable fabrics are far superior to cotton, particularly if you'll be doing any hiking or wet-wading.
Except when traveling for dinner in the evenings, or otherwise being out and about when you won't be exposed to direct sunlight for very long, I strongly suggest wearing long sleeves at all times. All fisheries in this region are at high elevations and the sun is exceptionally bright. My clients who get the worst sunburns are invariably from regions with beaches; they have beach tans, but beach tans don't do much to protect you from mountain sun. Contemporary lightweight quick-dry longsleeve clothing is as comfortable to wear as cotton tee-shirts and shorts, and dries faster if you get rained on or wet-wade. Long sleeves also protect you from insects, brush, briars, and the like much better than short sleeves. I am almost never outside for more than an hour or so without wearing such clothing.
You should always bring the following items.
Also bring the following from June through August.
Also bring the following in April, May, early June, late August, September, and October.
Bring the following IN ADDITION TO Spring and Fall Items if you are coming from late September through early April. On warm days in late fall or early spring, the spring and fall items mentioned previously will suffice, but if it's cold you will want every stitch of clothing you can get.
Walter Wiese is Montana Outfitter #22001 (formerly guide #9530) and Madison River SRP Holder #297. Yellowstone Park trips are run in cooperation with and under the permit of YNP CUA holder Richard Parks.
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Website, text, and graphics by Walter J. Wiese. Photos generally by Walter J. Wiese unless noted.