Wasatch 100 Course

Today is your best day by a wide margin. High of 50°F, mostly sunny, light winds (3-12 mph WSW), and only a 16% precip chance this afternoon — comfortable conditions for moving fast on the Wasatch course. Get your longest or most exposed segments done today. With 13h 43m of daylight (sunrise 6:34, sunset 8:17), you have plenty of light for big mileage, but tonight's forecast is a hard stop: 88% precip chance with thunderstorms after dark. Be off the ridgelines and somewhere sheltered well before sunset.

Starting tonight and running through Monday, this turns into a sustained multi-day system. Sunday is 100% precip with rain and snow showers, highs only hitting 40°F, dropping to 32°F Sunday night with another round of thunderstorms at 83% probability. Monday continues with snow showers at 93% and a low of 30°F Monday night. This is not a drizzly nuisance — this is three days of wet, cold, and intermittent lightning on a course that runs above treeline on Big Mountain, Desolation, and the Lone Peak zones. Footing on the high segments will go from firm to slick mud to slushy snow quickly. Plan for significantly slower pace on any exposed terrain Sunday and Monday.

Snowpack data shows 37 inches average depth on the course, with Long Lake SNOTEL still holding 95 inches at 8,400 ft (SWE 39.7") on a falling trend — that's consolidation from spring warming, not a hazard, but it means you will hit continuous snow cover on north-facing aspects above roughly 7,500 ft. This snow is settling and firm in the morning, softening by early afternoon. Microspikes are worth carrying if you're running Big Mountain to Desolation Sunday or Monday — postholing through softening consolidated snow on those north ridges at pace is a real ankle risk. Stream gauges are from California stations (data mismatch for this location) — treat any canyon crossings as unknown and scout before committing.

If you're splitting the effort across multiple days, front-load Saturday afternoon with your priority segments. Sunday morning may offer a brief usable window before the system fully locks in, but be conservative — isolated thunderstorm cells in the Wasatch can spin up fast, and the Sunday night and Monday forecast gives you no margin for being caught high. Keep your Sunday and Monday running to lower-elevation and forested sections of the course (Millcreek corridor, lower Big Cottonwood) and save the ridgeline work for when this system clears.