Possibly not-crazy idea in certain cases
If there is ice available somewhere, perhaps your tarp/bowl resulted in a convex lens-shaped extra bit of water, or you can (somehow) locate a frozen pond or even deep puddle from a previous thaw, you can consider the possibility of making an ice lens and using it to heat up something dark (your tarp or something more convenient), and using it to then melt snow.
You could heat a dark surface then put the snow on it, or put dark object on top of a layer of snow in/on something that can collect meltwater. Don't try to shine the light on the reflective snow!!
You don't need to make anything even close to an optical quality lens, you are not trying to set
ants kindling on fire, just warm something at a rate well above the rate than the air is cooling it, so that it can do substantial melting.
Anything you can do to insulate the warmed material so that it doesn't lose heat to the environment rather than to melting snow is important. Anything you can do to maximize contact area of the warmed object with the snow is important.
If the sunshine is intermittent, don't add more snow than you can melt quickly. Raising snow from -20°C to zero, then watching it get cold again is a waste of sunshine.
Bright sunlight on the ground can be estimated from the 1.5 atmosphere solar standard. From data in an answer to Does sunlight warm an astronaut's face during a spacewalk?, we can estimate that there is roughly 400 W/m² in sunshine near the ground, but it varies a lot depending on time of day and other atmospheric factors. Perhaps 50% of that will get through a lens made out of water ice (dirt, bubbles, and further absorption of infrared due to water and organics) so a 30 cm diameter ice lens will deliver maybe 20 Watts. That's 20 Joules per second or 5 Calories per second.
Heat of fusion of water is 80 cal/gram, so that's roughly 4 grams of water every minute, or 240 grams/hour, or maybe 1.5 litres per day on a good day.
That really might help extend life somewhat in a pinch.
What it might look like
From the question Has anyone ever tried to make a simple telescope using ice?:
From http://wildwoodsurvival.com/survival/fire/ice/ist.html also see Fire from Ice
This is not so likely what you'll be doing, but included for completeness: