A Special Weather Statement has been issued by the National Weather Service for light mixed winter precipitation possible over much of Northwest Oregon Monday and Monday evening. A very weak front moving onto the coast Monday morning and inland late Monday morning and afternoon and Monday evening will encounter a cold dry air mass in place over much of Northwest Oregon. Some of the moisture with the system will tend to evaporate before reaching the ground, but there is increasing confidence that some light snow, sleet or freezing rain will fall, especially in the colder sheltered valleys of the Coast Range and the Cascade foothills, in the inland valleys including the Willamette Valley, the Columbia River gorge and the Upper Hood River Valley.
The moisture will reach the Coast and Coast Range first Monday morning but any winter precipitation at the Coast will be brief. The winter precipitation is expected to reach the coastal valleys Monday morning, and possibly even into the South and Central Willamette Valley before noon and before temperatures have a chance to rise above freezing. The moisture will spread across the remainder of Northwest Oregon Monday afternoon, likely not reaching the Hood River area until late Monday or Monday evening where a little light snow is the most likely outcome.
Once temperatures inland slowly rise to above freezing Monday afternoon, the threat of freezing rain will diminish and the main threat will be a rain or snow mix as highs Monday may stay in the 30s. Amounts inland are expected to range from a trace to a few hundredths of a inch at most, and these limited amounts will likely limit the ultimate impacts. Nevertheless, those traveling in Northwest Oregon should use extra caution and be prepared for the possibility of some wintry conditions.