It’s been a mainly dry weekend across the metro area, in fact officially we didn’t have measurable rain in Portland
We won’t see any rain tomorrow, and then maybe .25″ to .50″ Tuesday afternoon/evening before the rain “clock resets” for 2020 at midnight Tuesday. This means 2019 will likely go down as the 7th driest on record in Portland. Those records at PDX go back just under 80 years. This is our 2nd consecutive dry year after a few wet ones. By the way, there is no significant long-term shift in our precipitation; go back 100 years and we picked up about the same as now. Temperature of course is a different story
Speaking of 2020, how is it looking for your party plans weatherwise? The good news is there won’t be snow or ice ANYWHERE over or west of the Cascades. A very warm airmass surges in with southerly breezes Tuesday afternoon. Sticking snow will be well above the timberline on Mt. Hood. Here in the lowlands a strong westerly flow overhead means we’ll be somewhat “rain-shadowed” by the Coast Range. It’ll be rainy at times Tuesday evening/night, but nothing heavy. South wind may gust 30 mph or higher too.
Up in the Cascades it’ll be a different story. All models produce a LOT of rain from 8pm-4am New Year’s Day. I highly recommend skiing during the daytime Tuesday when rain will be light. It should be a downpour during the overnight hours, especially leading up to midnight. Take a look at 24 hour rainfall from the WRF-GFS model, ending at 4am Wednesday
You can see those black areas approaching 3″ rain in the Cascades. Yet some spots in the valley will only see one tenth that much (Hillsboro). That’s a clear signal of strong “orographic” lifting. A strong flow of air perpendicular to mountain ranges (westerly in this case) forces moist air to rise, releasing LOTS of rain!
So we’re wrapping up a drier/warmer than average December. That’s after a drier/average (rain/temps) November. The main feature of this cold season so far is a persistent split in the jet stream near the West Coast. This is happening while I write. Parts of the San Francisco Bay area and Monterey have been soaked today.
These last two “storm seasons” have been the most boring I can remember (for a weather geek) for this reason. Either upper-level ridging weakening storms over/west of us or a split jet stream sending energy south. Of course last year the action suddenly picked up in early February with cold/stormy/snowy weather. At this point, 2019-2020 storm season looks just like last year…so far. I think we’ve seen ONE marginal high wind warning on the coastline in two months! No storms in the Willamette Valley, no freezing rain, snow, or stretches of days with heavy rain/wind. Cascade snow pack as of late December is tracking similar to those rough years 2014, 2013, & 2004. About 3/4 of the typical snow pack we’d see on the ground around Mt. Hood is missing this year.
THERE MAY BE A CHANGE AHEAD…BUT I’M NOT SOLD ON IT YET
For a quick summary, head down to the next headline…
Here’s the scoop, note the 500 millibar map for tomorrow morning. Ridging building in over us while that disturbance soaks parts of California.
New Year’s Day: A cool trough is passing by as the flow turns westerly overhead. Showers and lower snow levels mean some snow in the Cascades after the New Year’s Eve soaking.
All models are showing this as the beginning of a pattern change where a strong upper-level ridge develops out around 160W longitude; a preferred spot if you want cool/cold winter weather in the Pacific Northwest. Take a look at the 10 day forecast from the GEM/ECMWF/GFS models. Actually these are the ensembles from each of those models. Big ridge south of Alaska and cold upper-level troughing over us. Each model is a bit different, but the same idea and they all get to this pattern by days 10-15 out in time. So theoretically we’re headed into a cold weather pattern beyond Friday and of course we can get low elevation snow out of this setup if things work out right.
BUT, models keep pushing that change out in time. For example, this morning’s run of the ECMWF has a temporary ridge popping up over us Friday.
Just two days ago it showed a very cold trough bringing snow down at least to 1,500′ for Friday
And farther ahead, for the middle of next week, the features are shifted farther east on current model runs compared to what we were seeing 1-3 days ago. A ridge closer to us means the lack of normal stormy weather would continue into early January (rainy/windy storms). It also means Cascade snow gets shunted to the east too. Just two days ago models were showing many feet of snow in the Cascades this coming Friday-Sunday. Now we’re down to a foot or so.
So my concern is, for some reason, models still may not be catching onto the correct future placement of these features. They are giving up on this persistent pattern we’ve seen since October. This happened about six weeks ago too. Remember in mid-November it suddenly looked like a very wet and cool period was ahead and we’d be done with the weak weather systems? Rain for six weeks on the models? I know this is hardcore weather geek stuff so I’ll summarize
SUMMARY OF WHAT’S AHEAD
- New Year’s Eve will be wet, but not a soaker in the lowlands
- New Year’s Eve WILL be a soaker in the Cascades…all rain up there
- A Pacific cold front should drop snow levels down to at least 2,000′ or a little lower next weekend.
- We MIGHT see a change to colder weather for NEXT week (6th-12th), but at this moment there’s no sign of a lowland snow “event” in the next 9 days. That’s through Tuesday the 7th.
And by the way, Monday looks like another very nice day for late December…just partly cloudy.
For the skiers/snowboarders, here’s the Government Camp 7 Day forecast. Should be some good snow Wednesday and then again next weekend. Hopefully this will be enough to get Skibowl, Hoodoo, and Willamette Pass opened for the last few days of Christmas Vacation.
Chief Meteorologist Mark Nelsen