"Seems somewhere in the info overload I read that heavy rains can wash away nectar from flowers? Is this right?"
it is not that the rains have 'washed' the nectar away. heavy rains and no rain or dearth both affect pollen and nectar flows, bees need both. plants that would normally bloom in 'normal' weather conditions with either extremes may not bloom or produce either nectar and pollen for the bees. also in rains, like les said, the bees can be somewhat confined to foraging for what is available to them. so they fly when they can, and bring in what they can between rains.