The National Severe Storm Laboratory in Norman, OK has issued a Severe Thunderstorm Watch for a large portion of northwestern Oregon, including Portland, Salem and Eugene until 9 p.m. Thursday. (The watch ends at the Oregon/Washington border. Vancouver is not included.)
A Watch means conditions are right for severe thunderstorms, defined as either carrying large hail or wind gusts of at least 58 mph, or carrying a tornado. In the Northwest, it's usually the hail that makes the storm qualify. Watches are usually for a wide area and are issued by that NSSL Lab in Norman.
A Warning would mean that a severe thunderstorm is imminent or occurring. Those are usually issued by county and are given by the local National Weather Service office.
Now, Severe Thunderstorm Warnings are rare but not unheard of in Western Oregon and Washington -- usually a couple a year.
But a Severe Thunderstorm Watch? I've asked around and between me and some other National Weather Service sources, we have never seen one issued for Western Oregon before. Eastern Oregon and Washington? Yes, on occasion. But west of the Cascades, this might be a first.
Conditions are just right with an upper level low pressure system destabilizing the atmosphere and intense heat in the area making a volatile recipe for strong storms to develop.