What to Wear for Races This Weekend (Sept. 12–13): Big Cottonwood's 51°F-to-81°F Swing, Erie's 68° Dew Point, Bozeman's 35° Wind Chill

Friday's read — Three races this weekend need three different kits. REVEL Big Cottonwood leaves Guardsman Pass at 6:45 a.m. Saturday in 51°F air and finishes at Cottonwood High School where the grid shows 77°F at 10 a.m. and 81°F by 11. Erie starts Sunday at 7 a.m. in 69°F over a 68°F dew point. Bozeman's half goes at 8 a.m. into 43°F with an 18 mph east wind, which works out to about 35°F on your skin.

Thursday's numbers were close to these, but the details moved. Erie's humidity at the gun climbed from 96% to 99%, the storm risk at Guardsman Pass fell to 1%, and Manchester-by-the-Sea's rain chance is now 70% at 9 a.m.

How hot does Big Cottonwood get between the pass and the finish?

A 30-degree climb for anyone out past four hours. Open-Meteo's model runs cooler at the top (48°F at 7 a.m.) and hotter at the bottom (84°F at 11 a.m.), so if anything the NWS grid is the gentle version. Sunrise at the pass is 7:04 a.m., so the first 20 minutes run in half-light.

The air is dry — a 33°F dew point at the top — so 51°F feels like 51°F, and about 5,000 feet of descent warms your core fast.

So what goes on at Guardsman Pass?

Run in the kit you would want at 70°F, and wear a second kit you plan to lose. REVEL's own race page says throwaway gloves and Mylar blankets are handed out at the start, that drop bags must be in the trucks by 6:30 a.m., and that aid sits about every two miles.

• Race kit: singlet or short-sleeve tech tee, short-inseam shorts or 3/4 tights, a cap for the second half. The last 8 miles leave the canyon into full sun.
• Throwaway layer: an old fleece or long-sleeve you will not miss. The half hour before the gun is the coldest part of your day, and you will be standing still for it.
• Gloves: take the free pair. Drop them near mile 4 as your hands warm.
• Finish bag: sunscreen, a dry shirt and sunglasses. At 81°F with 33% humidity the finish-line problem is sun, not chill.

Half marathoners start at Mill D at 52°F and, even at REVEL's 15:00-per-mile cutoff pace, finish by about 9:46 a.m., ahead of the heat.

What do you wear when the dew point at Erie is 68?

The rain chance at the gun dropped from 18% on Thursday to 7% today, and the temperature barely moves over four hours. What matters is the gap between 69 and 68. With the dew point a degree under the air, sweat cannot evaporate, so cotton, thick waistbands and linings turn heavy by mile 10.

• A singlet over a crop or sports bra, not a tee. Less fabric to soak.
• Split shorts or a 2.5- to 3-inch inseam with a gel pocket. The Erie race preview has the aid station spacing and the four past race mornings.
• Anti-chafe on the inner thigh, bra line and underarms, applied twice as heavy as usual.
• No throwaway layer needed at 69°F.

Open-Meteo agrees closely here: 66°F with a 65°F dew point at 7 a.m. Start slower than goal pace for the first 10K; a sticky morning costs you late, not early.

Is 43 degrees in Bozeman colder than it sounds?

Yes, because of the wind. The NWS grid shows 43°F at 8 a.m., a 42°F dew point, 96% humidity, a 20% shower chance and an east wind at 18 mph. Run the standard wind-chill formula on those numbers and you get about 35°F. Open-Meteo puts that wind nearer 7 mph; pack for the windier model.

The race page lists the course at 5,000 feet, and half registration runs to 11:59 p.m. MT Saturday at $135. If the wind forecast drops, lose the gloves first and keep the sleeves.

Which of this weekend's smaller races need a rain plan?

Start times and entry details for all ten races are in this weekend's race list, which we updated with these same Friday numbers.

What does a long-sleeve base layer cost, and does it need to be expensive?

For one cold, windy morning like Bozeman's, fabric matters more than label: synthetic dries, modal and cotton hold water. Three price points:

• Around $12: Bubblelime's UPF 50+ V-neck long sleeve, quick-dry, in black and sized XS–4XL. Good: cheap enough to wear as a throwaway at Big Cottonwood, and the size range is wider than most. Not so good: it is a sun shirt, not a thermal, so on its own it will not stop an 18 mph wind; wear it under a singlet or add a vest.
• $40–$60: brand-name running long sleeves with thumbholes and a brushed inside. Warmer, and the thumbholes stand in for gloves.
• $80 and up: merino blends. Best with sweat and chill together, but not something you leave on a mountain pass.

Our fall running-in-the-dark gear notes cover lights and vests for the early starts, and the sister site's inseam-by-height guide helps pick tights that actually reach the ankle.

How much can Saturday's forecast still change?

For temperature, a few degrees. Between Thursday and Friday, Erie held at 69°F and Guardsman Pass went from 52°F to 51°F. Rain and wind move more: Manchester has gone 23% to 65% to 70% in three days, and the models split on Bozeman's wind by 11 mph. Above 30% rain or 10 mph wind, pack both options and decide in the car.

Our general what-to-wear-by-temperature chart takes it degree by degree, and the first race checklist covers the night before if this weekend is your debut.

Should you run in a rain jacket at Manchester?

No. At 65°F any shell is a sauna within two miles; a brimmed cap is the only rain gear worth wearing.

TL;DR — Big Cottonwood: race in summer kit, wait at the pass in a throwaway, pack sunscreen for an 81°F finish. Erie: least fabric possible, chafe protection, start slow. Bozeman: long sleeves, tights and gloves against a 35°F wind chill. Manchester: a cap, not a jacket.

More on the weekend race index, the daily weather page (Saturday and Sunday editions go up in the morning), half and 5K coverage and marathon previews.

Sources

• Forecasts: National Weather Service hourly gridpoint data for each start and finish location, retrieved Sept. 11, 2026, 7:40 a.m. ET; cross-checked against Open-Meteo hourly model output the same morning. Wind chill calculated with the NWS wind-chill formula.
• Race logistics: runrevel.com/bcm/info (start times, bus loading, drop bags, aid spacing, cutoffs); eriemarathon.net; the Bozeman Marathon registration page (start address, pricing, deadlines).
• Product details and price: Bubblelime's product listing, checked Sept. 11, 2026.