In an effort to answer this question, Portland’s National Weather Service office has charted out potential rainfall totals for the Willamette Valley.
According to the chart, Portland has almost a 100% chance of seeing at least 1 inch of rain by Saturday morning, and a 67% chance of 2 inches of rain. The chart also states that Portland has a 37% chance of seeing 3 inches of rain. Although unlikely, there’s also a 15% chance of 4 inches of rain in the metro area.
“Bottom line is that today will probably be our wettest day so far this season,” the NWS stated on social media Friday. “We are not expecting widespread flooding, but localized issues are certainly not out of the question. The best chances for these issues are along the coast, north Coast Range, and areas impacted by wildfires these past few years.”
The chart also gives rainfall probabilities for the Kelso, Corvallis, Cascade Locks and Salem areas. Of all the included areas, the Cascade Locks has the highest chance of seeing 3 to 4 inches of rain, with a 42% chance of at least 3 inches, and 22% chance of 4 inches.
The abundant rains will increase the chance of flooding in urban areas, creeks and flood-prone riverbanks across Northwest Oregon and Southwest Washington on Friday and Saturday.
“The Portland metro area will also see plenty of standing water on the roads, especially during this evening’s commute,” the NWS said. “So, give yourself plenty of time and please be patient.”