I have two ideas. First the cool weather is keeping the pollinators away and so the young squash does not form. Second, zucchini are heavy feeders and if the plants are in the same spot as last year the soil could be depleted and need more fertilizer. Also, the first squash formed are from unfertilized female flowers. Harvest these first young zucchini as soon as they form. This tip will encourage the male flowers to develop which will then pollinate the female flowers so the crop will be more productive later in the summer. Don't give up -  summer should heat up soon and you can still get a great crop. Keep growing, Marianne Binetti