Temperatures are surging in western Washington today (Friday). Yesterday was warm enough, with highs reaching the mid-80s over Puget Sound, and over 100F near Portland and the eastern slopes of the Cascades. Look closely and you will see some 90s over the eastern and southern slopes of the Olympics where downslope flow gave a temperature boost.
Today will be warmer.
Temperatures aloft have warmed further and easterly flow has developed over the crest and western slopes of the Cascades, as illustrated by a time-height cross section over SeaTac Airport (time on x axis, height on y axis). As a result, temperatures will surge over the western slopes of the Cascades (into the upper 90s in places)
Seattle-Tacoma Airport reached 87F on Thursday and currently it is running 8F ahead of yesterday, which suggests strongly it will reach into the lower 90sF today.
But we won't break really big records and temperatures near Seattle won't get into the upper 90s F as some folks were suggesting. Why? Because the thermal trough, the area of low pressure associated with low-level warm air, is centered south of us, resulting in a modest north-south pressure difference (higher to the north). As shown in the temperature, wind and pressure forecast for later today (below), this will cause northerly winds that will move cooler air into Puget Sound. Still warm, but not crazy warm. The easterly flow is also bringing in slightly cooler air aloft. Furthermore, sinking on the western slopes of the Cascades will produce some leeside troughing (low pressure) along these slopes, which will increase the north-south pressure gradient (again bringing in somewhat cooler air).
Those poor folks in Portland don't enjoy this natural air conditioning and will burn... heading above 100F. At least they have fine microbrews to cool down with.