The time has come. You’ve put in the work, run the miles, and crushed a slew of strength sessions. Now as you approach the Spartan World Championship on Saturday, September 30, you have one last battle to win: the one against the mountain itself.

Held at the venue that hosted the 1960 Olympic Games, The World Championship Beast in Tahoe is known for its gnarly and unforgiving terrain. But this year the race will be even bigger and badder, presenting 40 obstacles over a 16.2-mile course that climbs to an elevation of 9,000 feet. If that scares you, good. If it gets you excited, even better. Because it means you’re ready to start thinking about how you’re going to crush it. With that, here’s what should be on your mind now.

How to Plan

Expect the unexpected. “The weather in Tahoe can change rapidly this time of year, especially if a rain cell passes through,” says Tony Fuentes, meteorologist with the National Weather Service. “Snow isn’t out of the question, either. You have to be prepared for anything that can come your way.”

The temperature, says Fuentes, can vary from 30°F to 70°F over the course of one day, with gusts of wind up to 60 mph. So plan on checking the forecast a week before the race, and then check back daily as the race gets closer. Weather predictions become more accurate as the event draws near, so your best packing decisions will be made in the 24 hours leading up to the start of the race. “If there's any mention of potential thunderstorms in the forecast, that’s a cue that you could have rapid changing conditions out of nowhere,” says Fuentes.

How to Pack

Even if the weather in Tahoe remains steady, you’ll still be climbing mountains, crawling under barbed wire, running through mud, and swimming through water. And that last one, the swim, can leave you freezing cold and soaking wet. How do you combat breakdown-level misery and potential failure? By making sure your gear is as dynamic as the weather is unpredictable.

Use Your Back The varied nature of this race makes carrying a pack almost essential. But swap out your bulky 30-liter day-hike bag for one that’s small and designed to hold tight to your frame while you run. A good option is the Camelbak Circuit Vest, which will also help keep you hydrated between water stations.

Double Up on Layers. Inside that pack is where you’ll pack extra dry clothing or cold-weather essentials that can help you handle the potential 40-degree temperature swings. Just stuff clothing into dry sacks or waterproof Ziplock bags. That’s how Ashley Seeger, a competitor at last year’s Beast, managed to stay warm. “I chose to strip my shirt off before getting in the water, putting it in the waterproof bag and swimming across," she wrote in a post-race blog post. After the swim, she put the dry shirt back on. And she did the same for the dunk wall.

Megan Sloan, who raced the Tahoe Beast last year, echoes the quick-change strategy. “Absolutely everyone I saw was shivering and miserable after the swim, miles after the swim, and were mostly unable to warm back up," she says. “Taking the time to change could actually save your race.”

Another thing: “Watch the weight or bulkiness of your layers,” says Sloan. Overheating can hurt your performance as much as being cold, so Sloan recommends several light layers, instead of one or two big ones. “When I didn’t want to throw on too much weight, I opted for Hot Hands hand warmers for when I was absolutely freezing," she says.

Pack extra options in your luggage, and then take the time to look at your stash the day before the race, after you’ve checked the weather. It’s better to bring too much and have the ability to be selective instead of wishing you had more gear.

Wear Only What Wicks. Don’t race in anything made of cotton; it holds water and dries slowly. Instead, opt for sweat-wicking merino wool or a synthetic fabric that will help keep you dry (and thus, warm). A good example: The Workout Ready Long Sleeve from Reebok. It’s 100 percent polyester and costs just $28.

Check Your Head Even if you don’t need them at the starting line, make sure you have a beanie or hat, plus a pair of lightweight gloves, in your bag. They might save you when the winds pick up at higher elevations. And opting for a hat with a brim can keep rain out of your eyes if the sky decides to open up while you’re hitting those downhills.

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How to Eat

You’ve already trained like a Spartan. Now it’s time to eat like one. As with any endurance race, it’s important to fuel appropriately before and during. What you eat can be the deciding factor between a strong race a painful crawl to the finish line.

Prep Warm Fluids Although you will find water stations scattered throughout the course, Seeger says that having a thermos at her transition area provided the morale boost she needed when the cold was getting to her. She recommends putting an electrolyte tab into warm water before the race, packing it into a thermos, and taking a short break to sip it like tea at the transition. Just don’t rush to chug it down and risk burning yourself. __Don’t Skimp on Salt __The government recommends about 2,300 milligrams of daily sodium in your diet. But when you’re training for an OCR, it’s important to get at least that—and more if you're sweating. A good goal is to take in half your bodyweight in ounces of fluid each day, but during the days leading up to Tahoe, start swapping out some of those ounces with an electrolyte fluid source. That will help stave off cramps between obstacles. For during the race, Sloan recommends caffeinated salt tabs (like those from SaltStick).

BYON (bring your own nutrition) Any veteran of the Tahoe Beast will tell you that carrying calories on the course is a must. “You’re working really hard, so your body needs help,” says Sloan. “For me, foods like Larabars, RX bars, or nature valley bars were perfect. Also, fruit like mini oranges or raisins for sugar and energy, Clif Bloks, or even peanut butter sandwiches.” Aim to consume 90 to 200 calories each hour, and follow the “nothing new on race day” rule. Prep your body, trying out different food combinations while exercising, to see what feels right for you.

Can’t make Tahoe? Here’s everything you need to know to find your race.