Grand Canyon Rim-to-Rim

Sunday is the primary hazard. A 62% precip chance with 'showers and thunderstorms' forecasted means real lightning exposure on the South Rim, North Rim, and the open stretches of the Tonto Platform where you have zero shelter. At 18–25 mph SW winds, storm cells will move fast and give limited warning. If Sunday is a major mileage day, you need to be off both rims and below the canyon walls by 1 PM at the latest. That's not conservative — that's just the geometry of canyon lightning. Plan your Sunday segment to put you deep in the canyon (Phantom Ranch corridor) during the afternoon window, then push to the rim in the evening once Sunday Night shows only 6% precip and partly cloudy skies.

Tonight (Saturday) has a 72% chance of rain showers with 13–17 mph winds. Trails — especially the switchbacks on the North Kaibab and Bright Angel — will be wet and potentially slick on clay sections come Sunday morning. The inner canyon's Tapeats sandstone gets greasy when wet. Factor that into your footing and pace on the descent sections, particularly the steeper pitches below the rims. This isn't a stopper, just worth knowing before you're already moving fast on loose wet rock.

The SNOTEL data (Annie Springs at 6,021 ft showing 14 inches, falling trend) tells you there's residual snowpack on the North Rim above 8,000 ft. The North Kaibab trailhead sits around 8,250 ft and has seen snow this week. Expect patchy snow or icy sections on the upper North Kaibab, especially in shaded switchbacks. Softening by midday but potentially firm and slick in the early morning hours on Saturday and Sunday. Not a technical problem, but worth accounting for in your opening pace out of the North Rim.

Monday is the gift — 79°F, sunny, 4% precip, light winds. If you're doing a multi-day and have flexibility, stack your big effort or final push for Monday. Heat is manageable at 79°F in late April as long as you're running with full hydration capacity; inner canyon temperatures will run 10–15°F hotter than the rim, so expect 90°F+ at river level on Monday afternoon. Water sources at Phantom Ranch, Indian Garden (Havasupai Gardens), and the North Rim corridor are reliable this time of year. With 13.5 hours of daylight (5:43 AM to 7:11 PM), a full rim-to-rim running around 24 miles needs roughly a 2.5 mph average — very achievable, but the Sunday storm window means your start time matters more than your pace.