A historically warm winter has left parts of Oregon's Willamette Valley with little to no snowpack, and federal water managers are now rethinking how they will operate 13 reservoirs before summer really kicks in. The U.S. Army Corps of Engineers' Portland District says the lack of snowmelt is already reshaping the region's water outlook as drought conditions worsen. What's happening? During a May 19 online town hall, Army Corps staff said they a…