As usual the Portland forecast when snow is possible is not at all clear cut, but Ill try to sort it out for you and give some insight to the processes at work. The overall set up is a good one, with cold, dry (thats actually important) Arctic air pouring out of the Gorge. Low pressure, better yet, WEAK low pressure, but with a lot of moisture, is coming in from the southwest. Question is, will it stay cold enough long enough for significant snow or freezing rain in the valley? For Portland, I think well likely see snow begin in the morning around 7 am. Temperatures wont be much below freezing, but, as the precipitation falls into the very dry air, evaporative cooling processes (this is why the dryness of the air matters) should be enough to cool the air to keep the precipitation as snow. Im thinking there may be a brief period of freezing rain before we transition to a cold rain around mid-day. So for Portland: Trace to 3 of snow, with 4-6 possible in the hills, before the change to freezing rain and rain that tapers off Thursday night. South of roughly Wilsonville, there should be less snow and a quicker changeover to freezing rain and then rain. The Gorge is under a Blizzard Warning! Rare for even the Gorge. 4-10 inches of snow will fall in the Gorge as winds gust to 70 mph at the western end of the Gorge, reducing visibility to near zero at times. Friday should see an end to all precipitation and some partial clearing. More cold air funnels south from Canada this weekend, but it should be mainly sunny and not as cold as the current Arctic Blast. Look for lows in the low 20s in the valleys and highs near 40-degrees. And more strong east winds. Stay tuned for more on this significant weather event for the Portland area overnight. As the storm approaches, there may changes and fine-tuning to the forecast.
Posted on: Thu, 13 Nov 2014 00:32:18 +0000
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