Snow fell on Mauna Kea overnight as a weather system in the upper atmosphere lingers over the islands. National Weather Service forecasters say thundershowers are possible over all islands Thursday and Friday.

Cold air in the upper atmosphere combined with the usual tradewind showers in the lower atmosphere is creating unstable and potentially wet weather through the end of the week.

A winter weather advisory remains in effect for summits of Mauna Kea and Mauna Loa through this afternoon because of the chance of freezing rain and snow.

The weather system in the upper atmosphere has moved off to the southeast and weakened slightly, said Victor DeJesus, a forecaster with the National Weather Service.

"For today, the heaviest chance of rain and thunderstorms is in the eastern part of the state on the Big Island and Maui," he said. 

But the system is strengthening and may move west Thursday and Friday, bringing the chance of heavy rain and thundershowers to all islands.

"There’s a lot of moisture around," DeJesus said. "It’s very cold in the upper atmosphere so that will enhance any tradewind showers. It’s going to be a real wet tradewind pattern with the chance of thundershowers."

The tradewinds should keep the rain moving and lessen the chance of flooding. But, DeJesus noted that there’s always a chance that showers could linger in one place and the ground is saturated from Wednesday’s rains.