There was some precipitation on the the night of 2/20-21, but temperature was in the low 40's that day, so it would have melted.
The 2/28 shows about 0.15 inches. If it was all snow, it would 2.5" inches max. However, some of it fell just at the freezing mark, so it could have not collected on the ground. The next day, it was above freezing.
It is not a question of when people started looking. Passers by will see a guardrail or fence broken, or parts of the car still laying there next to the river.
I think there is only one spot where a truck could go into the river without hitting a barrier.