This will potentially bring increasing air stagnation concerns as valley inversions strengthen under persistent high pressure and increasing subsidence. Not much change beyond Wednesday as offshore flow persists but weakens considerably during the middle of the week. Valley locations will likely be a few degrees cooler but should still get into the upper 50s during the first half of the week. The coast will likely be the warmest part of the forecast area as downsloping off the Coast Range helps temperatures climb into the 60s in several locations by Tuesday. Offshore flow will also support warmer temperatures during the first half of the week as 850 mb temps climb from around 7 C Monday to 10-12 C for Tuesday and Wednesday. Will also likely see 20-30 mph gusts make it into parts of the valley at times. This will support blustery conditions through Tuesday night with gusts to 50-60 mpg in the Columbia River Gorge, 40-50 mph in the high Cascades, and 30-40 mph gusts in the higher terrain of the Coast range. Winds will ramp up on Monday as the KTTD-KDLS pressure gradient increases to around 7 mb and the KOTH-KGEG gradient reaches 15 mb. This will tend to limit fog and stratus coverage relative to last night, but still expect at least some development overnight into Monday morning favoring more sheltered areas such as the south valley and the Lower Columbia Valley. Offshore flow will also develop this evening and strengthen through Monday as surface high pressure builds into the Columbia River Basin. Otherwise, expect remaining scattered mid and high level clouds to continue to clear the area from north to south this evening as a closed upper low presently located off the south Oregon Coast drops south along the California coast and allows a stout upper level ridge to build over Vancouver Island. At least some stratus is likely to linger through the rest of the day in the south valley under light northerly surface winds. Low clouds have been slow to erode in the interior valleys this afternoon, with a low stratus deck and some patchy fog finally dissipating across the northern half of the area but continuing to linger in the central and south Willamette Valley as of 2 PM. East to northeast winds will be blustery at times, especially near the Columbia Gorge and across exposed slopes and ridges of the Cascades. High pressure and offshore flow will bring dry and increasingly mild weather through the first half of the week. UPDATED National Weather Service Portland OR
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