We have a challenging long range forecast (still!) this afternoon…that would be an understatement. But first, the shorter term.
A weak cold front is moving through the region now, headed off to the southeast. Not much rain with this feature this evening. Then we gradually clear out on Tuesday.
Tuesday night, colder high pressure slips east of the Cascades, giving us a round of strong east wind through the Gorge and out into the eastern side of the Portland Metro area. Previous model runs were a but stronger with this, but the WRF-GFS cross-section still shows 40kt speeds above the surface at PDX Wednesday morning (where it says 11/12, that’s January 11th at 12z, or 4am). 
Windspeed in the western Gorge should be similar to the last event…lots of gusts around 60 mph, with 90 or so at Vista House during the day Wednesday. Possibly Thursday too, but the wind dies down quite a bit Friday at the latest. This surge of east wind will be cooler than the last as well. High temps, even with the sunshine, will only be in the lower 40s in the metro area Wednesday. The dry air and clear skies mean wind-sheltered areas (Hillsboro!) will drop down around 20 Wednesday and Thursday nights. The chilly December weather is coming back for a few days.
Friday and Saturday look uneventful, especially on the GFS and ECMWF models. Just a return to onshore flow and dullness; probably dry.
So where are we with possible colder, wetter, or snowier weather?
We can probably rule out only one thing right now; it’s unlikely we’ll see any sort of big arctic blast through the 6-8 day period.
Just about everything else is still on the table Sunday and beyond. That would be: mild and dry next 10 days, or wet snow to sea level in very cold onshore flow, or possible windstorm next week, or just cooler and wetter with no valley snow but lots in the mountains.
The GFS model (NOAA’s long range forecast model) continues to stubbornly insist we’ll stay mainly dry and mild through the foreseeable future. Here is the 18z (latest run) GFS ensemble chart. Note the operational run is clearly way up in the “warm area” if you go out to about next Monday. Check out how many of it’s ensemble members are significantly colder, some as early as Saturday night. By the way, the Canadian model is showing snow near sea level as early as Saturday night too with an upper-level trough digging south more rapidly than the GFS.
Now check out the 12z ECMWF ensemble chart: 
Some nice info can be gleaned from this one. The ECMWF operational model has a strong cold front moving through here on Sunday, with temps cold enough Sunday evening to bring snow down into the hills. Precipitation tapers off Sunday night, so not a big deal anyway, but still, quite a change to cooler and wetter weather. But look at the chart above, I notice it’s right in the middle of it’s ensemble members, so quite supportive of itself I guess you could say. Note the large number of ensemble members that bring in the cold a day earlier, much like the GEM and some GFS members. This will be interesting to watch…could the timeline for the first deep trough move up a day?
So what’s my preference? Totally undecided, I don’t think anyone forecasting lowland snow (or continuing mild and dry) is doing anything more than guessing; still far too much model indecision. Up until today, the “change” has been outside the scope of our forecasting here since we just do a 7 Day forecast. But it’s time to buckle down and we’ve chosen to go with the ECMWF, as I often do. So our 7 Day forecast goes with it. Very light rain or showers Sunday as the cooler air moves in, then drying out Sunday night and Monday ahead of a strong system Tuesday. Precipitation is light at that time and 850mb temps are marginal for snow; combine that with the assumption that details will change with the next model run. That’s why we don’t have snowflakes on the 7 Day forecast for Sunday night or Monday morning.
To sum it up; I have advised Wayne Garcia not to bother putting on his studs yet. We MIGHT get through the next 7 days with no valley-floor snow issues. He’s hoping he can make through the next 5 weeks without them. After that he’s probably clear for the winter. Hard to believe the bulk of the “snow season” has passed already!
9:30pm Update: The 00z GFS just came in with no rain and mild through next Tuesday, then heavy rain the 2nd half of next week. A pineapple-express type setup with snow only way up on the mountain. Good news though, the 00z GFS ensemble chart shows it was just about the warmest member. There could still be hope…maybe. I especially like the ONE ensemble member that brings an 850 mb temp of -23 C. next Tuesday. Here’s the chart:
Chief Meteorologist Mark Nelsen
Posted by Mark Nelsen 
FOX 12 Weather Blog 