Well tomorrow is the “big day” for us weather weenies. I just finished perusing the 00z model runs…here are my thoughts:
1. South wind kept us from getting a 1-2″ surprise in the Metro area today. Models handled our little snow burst well, except the timing was off…it showed up 2-3 hours early. That light onshore flow was expected. Now it’s disappearing as a 2nd low is spinning down the coastline. It’s near Astoria right now; models show it spinning overhead and into eastern Oregon by morning.
2. Behind that low, a colder atmosphere is pulled down from the north overnight. That plus some clearing should make for an icy, but dry start Monday.
3. Between daybreak and around 4pm tomorrow, a stationary front (the leading edge of the arctic air) sits between Astoria-Portland-Condon. A 3rd surface low develops along the front and moves right overhead midday or afternoon. I’m depending on that to give us a possible 1-2″ of snowfall…a bit more moisture than models show (but that happened today too). We start cool again in the morning tomorrow, plus our model (RPM) and WRF-GFS show the boundary right over us, instead of up north of Kelso. That should mean no south wind and we shouldn’t have a problem getting snow to stick just about anywhere from Portland north.
4. The arctic front then suddenly makes it’s move behind the low after 4pm, sagging south to Eugene by 10pm tomorrow night. Most likely at least a trace of snow would accompany that front even down into Salem and Eugene. As a result, we should freeze up quickly after dark tomorrow.
5. If you have plans to be out and about after the noon hour tomorrow, make sure you have a plan to get un-stuck if we suddenly get a surprise 2″ dump of snow and traffic grinds to a halt! That seems unlikely, but definitely possible.
Now this is the scenario that I’m basing my forecast on. The NAM moves the low by a bit farther to the north, which puts us into a similar situation that we saw today (minus the eastern Clark County cold spot). If so, we’d only get a trace or so as the arctic front finally slides south.
So here’s my forecast:
1-2″ snow Portland north to Longview midday-evening tomorrow.
Trace from Woodburn south into the Valley.
I lowered Tuesday’s high temp forecast based on at least 1″ of snow cover in the metro area. If we don’t get snow on the ground, I’d guess 33-35 degree highs.
We can talk about that sudden appearance of moisture for Wednesday AFTER we get through tomorrow. Actually, I suppose you can talk about whatever you want on here, but I’m busy focusing on tonight and tomorrow.
It’s still hard to believe it’s such a cold atmosphere plunging into our area tomorrow night. -13 to -15 degrees C. at 850mb? Imagine if it was January…then it would be quite a bit colder at the surface. I’d probably go for highs in the low-mid 20s.
Chief Meteorologist Mark Nelsen