The Central Valley may see an unusually large outbreak of brown-and-orange painted lady butterflies beginning this weekend, after the sun returns, says UC Davis butterfly expert Art Shapiro. Earlier this week, the most painted ladies seen in 10 years were reported on the eastern slope of the Sierra Nevada, near Reno. While many of those will be killed in the snowfall expected today, Shapiro says, there could be plenty more coming along behind them. The butterflies in this migratory wave were probably born from eggs laid after heavy rains in February and March in the deserts of the U.S. Southwest and northern Mexico. Painted ladies are strong fliers. They benefit from weather conditions like the valley is seeing now, Shapiro said. They ride north on southerly winds just ahead of wet storms, getting into position to feed on the resulting fresh growth of weedy plants.