Snow on Maui and Big Island mountaintops are so far the most dramatic effects of unstable weather over the islands last night and today.

Cold air in the mid- and upper-atmosphere moving over the islands created unstable air conditions and the threat of heavy rain. But the National Weather Service has dropped a flash flood watch for Maui and the Big Island posted this morning.

Forecasters say the cloudy weather associated wit the disturbance has mostly moved past Oahu. But there were still clouds over the Big Island this afternoon.

Maui and the Big Island mostly got trace amounts of rain from the weather system overnight and this morning. The heaviest rain fell on Lapahoehoe on the Hamakua coast of the Big Island, which got nearly 2 inches.

Meanwhile, a large swell is predicted to bring waves  surf of  up to 40 feet to north shores of Oahu, Kauai, Niihau, Molokai and Maui beginning this afternoon. A high surf warning is in effect until 6 p.m. Friday.

Skies should start to clear with the usual tradewind weather returning by this weekend.