It’s a rule of thumb that when the willow buds begin to open it’s time for smelt run. Others are waiting for warm spring rain, after which the air temperature is maintained for several days in the range of 15 C.
However, without checking the water, it is rarely possible to say whether the right moment has come. Warm and windless evenings usually bring the right conditions. It may happen, however, that a strong wind will blow for a few days and smelts will not come near the shoreline.
It’s also hard to predict the exact time at night when smelts will appear. It’s a gamble.