First image is of the winds aloft at 850 mb (approx 5000 ft). Winds over the state were light and out of the north. Up north there are some 20 to 30 knot southerly winds that may discourage migrants from taking off.
Second image is a snapshot of the base velocity showing north to south movement.
Third image is an animated gif with snapshots every half hour of the base reflectivity above radar station RTX. Animation runs from around 8:00 pm pdst yesterday evening through 5:00 am pdst this morning. (Click on the thumbnails to view the full-sized images and animation.)
Sunset last night was at 8:01 pm pdst.
Radar was in precipitation mode most of the night but switched over to clear air for a while — densities were very light in that window.
As an aside, but relative to migration over Portland, i watch the reports from a banding station in BC Canada, Tatlayoko Lake Bird Observatory. They post their observations daily. Google them and check it out. They recently had a Long-tailed Jaeger hang out for three days feeding on grasshoppers — pretty cool! It came in last Sunday, the 21st. Go back and check out the winds aloft for that date and the comments to see why that bird is 150 miles inland.