Ahh, the good times are back this evening with some good heavy rain showers in spots (right over Steve Pierce's home). And now we have the possibility of snow to low elevations tomorrow night and Thursday. I just had the studs taken off my
"snow car", luckily it's a 4 wheel drive that'll do fine in a few inches of snow! For tonight…more showers. For tomorrow…more showers. A nice slug of moisture to our southwest keeps the showers going overnight. It still looks like the heaviest precipitation will be from the Columbia River south.
Then a sharp cold front moves into Northwest Oregon tomorrow afternoon. This is the leading edge of a very cold maritime polar airmass. Arctic air is already beginning to spill out of British Columbia between Vancouver Island and the Queen Charlotte Islands. So we get an upper-level low and a surface low spinning up near Northern Vancouver Island later tomorrow. These both pass overhead Thursday. 00z models all seem to be in agreement now on the movement. The surface low comes inland around Astoria as it fills Thursday morning. It's a really cold airmass! 850mb temps are somewhere around -8 to -9 deg. C. That's usually cold enough to get snow to sea level if you can get rid of a mixing wind. We still have a light southerly flow up the Willamette Valley tomorrow evening and Thursday because the low is staying farther north, but it's not exactly a raging south wind. Heavy precipitation intensity always helps in these situations, or is sometimes the key factor to getting snow to low elevations. With the westerly flow, the areas west of I-5 may have lighter precip. In general I don't see a ton of heavy showers. The steadiest precipitation should be in that 4am-10am time period Thursday…then we dry out in the afternoon (and warm up of course).
Put these all together and this is what I get: I think it'll be tough to get significant snow (>1") here in the lowest elevations of Portland, but all of us should see at least a dusting in the morning Thursday. I'd say 1-3"+ snow is a done deal at/above 1,000' anywhere in our region, and anywhere in SW Washington north of Vancouver. The Coast is a big question mark…there's no reason we shouldn't be able to get snow to the beaches, unless the southerly breezy from Astoria south kills it for you folks. We have 24 more hours to keep digesting information for this little event too.
Beyond Thursday, pretty quiet. A new upper level trough develops offshore Saturday through Monday. There are some deep surface lows that linger way out over the Pacific, but they aren't really going anywhere in a hurry, so they aren't a high wind threat for us…Mark Nelsen