As an amateur, I have to wonder about this, for the following reasons:
1. From what I've been reading, isn't the soil heavily saturated with water? Wouldn't that increase runoff?
2. It's February, and it's wet. How much evaporation will there be?
3. From what I've been reading, there is about 30 inches of water in the snowpack. The incoming storm is said to consist of tropical moisture, i.e. warm, and the snow has already been rained on, which makes it more likely to melt.
Only one-third of the rain goes into the reservoir? This seems pretty hopeful to me. I hope you are correct.