PORTLAND, Ore. (KOIN) – High pressure starts flexing its muscle Wednesday. That means we’re pumping up temperatures to nearly 90° the afternoon. Consider it a training day for the major heat we’re expecting on Thursday. A Heat Advisory, issued by the National Weather Service, will go into effect starting Thursday at 11 a.m. and last until 11 p.m. This includes the entire Willamette Valley and Rogue Valley down to the California border. Temperatures will swell to nearly 100° for Portland. If we hit 98° that will be a record tie for that day in the Rose City.