* WHAT...Temperatures as low as 33 to 36 degrees will result in frost formation. * WHERE...Willapa Hills and Adjacent River Valleys of Pacific and Wahkiakum Counties, Lower Columbia River and Cowlitz River Valleys, North Oregon Coast Range Lowlands, North Oregon Coast Range, Upper Hood River Valley, North Clark County Lowlands, and South Washington Cascade Foothills. * WHEN...From 11 PM this evening to 9 AM PDT Wednesday. * IMPACTS...Frost could harm sensitive outdoor vegetation. Sensitive outdoor plants may be killed if left uncovered.