Timing of flows on Mars
I obviously didn't make this clear enough in the website. I'll add a bit to it about timing.
For 2 months after first sunrise, the area is blanketed with white frost. No black streaks are seen at this time.
for 3-4 weeks, images show black threads cutting through white snow patches.
For the remaining 8 months of Summer and Autumn, the frost is gone, the ground bare, and no new dark streaks appear.
Then the frost reforms for the next winter...
So the flows occur ONLY at this specific time of year - the late spring thaw.