I would need to read solid evidence that snow was not a factor in them missing their turn-off. It is the most plausible answer imo. Nothing I have read about the case suggests anything else.
You obviously don't understand the locale and timeline.
It wasn't snowing down in the lowlands between the party's hometown area and the site of the basketball game (Chico). Yuba City and the adjacent Marysville are in the Sacramento Valley, at an elevation of only circa 60 ft. above sea level. The average daily high temperature in February is on the order of 60 F. Snow is rare in the valley.
It was at the intermediate town of Oroville where they got off on the Oroville-Quincy Road (now Highway). Coming from Chico they had to pass through or by Oroville to even get to the road. The most direct route from Chico to Yuba City would have bypassed Oroville entirely. Oroville's climate is the same as Yuba City's, and average February snowfall there is 0.0 inches.
As I pointed out in post #95 it's difficult to see how they could accidentally get onto the Oroville-Quincy road without noticing they were, or intending to be, in Oroville. Conversely, it makes sense if they were headed to Forbestown, where Mathias had known connections.
The weather conditions spanning the hometown and game site area of intended travel didn't require anything more than the light jackets some of the guys were wearing.
The car was abandoned at an elevation of circa 4400 ft.
Once they bypassed the hometown area and headed another (circa) 20 miles up into the mountains they eventually encountered substantial standing snow. The snow pack on the road where Madruga's car was parked was on the order of 8 to 10 inches. This spot was still short of the point where the rangers had already closed that road for the winter.
The car was stopped in the area where the snow line began. It wasn't like Madruga had been driving in packed snow for miles and miles. Recall that Schons / Shones had proceeded onward from the lodge (circa 8 miles back from the car abandonment scene) specifically intending to determine where the snow line began.
By the time the searchers were on the scene, the weather was completely changed. None of the pre-existing conditions were evident. The party was lost in February. The search discovers them months later, long enough for Weiher to starve to death in the cold.
The car was discovered on the mountain road (abandoned) by a ranger on February 25 (the day following their trip / disappearance). When the ranger learned of a missing persons incident, he notified the authorities about a car matching the missing one. The investigators went to the site, inspected the car, and retrieved it on February 28.
A major blizzard hit quite soon thereafter (perhaps starting late on February 28), obliterating everything and forcing suspension of search activities at or beyond the car abandonment site.
There were no significant changes in weather and / or snow pack between the night the boys disappeared and the day the authorities recovered their car.
It wouldn't be until the spring thaw that the bodies were found.
It must be borne in mind that the investigators seemed to focus on the notion Madruga's car had been abandoned by someone else (perhaps after having stolen it). They didn't seem to think the boys had wandered so far off course, and they didn't seem to seriously think the boys could or would have left the car and hiked even farther onward.
The investigation proceeded from February until June (when Weiher's body was discovered) with primary attention to possible leads back down in the valley / lowlands.