Late Evening Update

January 13, 2012

Lots of maps and model data to look over this evening and almost out of time so here are the basics:

  1. Still no change in my thinking for the weekend.  Not a whole lot of moisture to work with, but cold enough for sticking snow everywhere, especially outside of the main daylight hours (10am-4pm).
  2. You see our forecast on the previous post…a trace to 1″ in the lowest elevations and that’s what I expect officially here in the city.  Some isolated spots (regardless of the elevation) could see a little more if a cluster of showers passes overhead.
  3. Hilly areas (around 1,000′ and above) have a better chance at 1-3″ between sunset Saturday night and Monday afternoon.
  4. Increasing confidence that we could get a big snowfall (like last winter) in the foothills, above 1,000′ up to 2,000′, from Monday evening through Tuesday night.  If the GFS is correct on low center placement, maybe 6-10″ or even more.
  5. Same thing in the Gorge, if the GFS low placement is correct, the central and eastern Columbia River Gorge could get a good 10″+ during the same period as easterly flow develops later Tuesday through Wednesday morning.  Note the map:

More thoughts…

I’m feeling pretty confident right now still about the 72 hour forecast (through Monday afternoon).   From sunset tomorrow night through at least Tuesday morning the snow level will linger at or near sea level.  At no time during that period should the sticking snow level climb above 1,000′ or so.  But brief high temps around 40 in sunbreaks Sunday and Monday mean showers could easily pass over during those times with little/no snow sticking, another reason to “lay low” on metro area snow amounts.   Notice the WRF-GFS snow maps continue to show very minor accumulations, as well as our RPM model…it shows 0.7″ snow by Monday afternoon over Portland.

The 00z NAM is slightly stronger with the northern stream and a 2nd trough dropping south late Monday and Tuesday morning.  Due to that, it’s showing a colder atmosphere, but not much moisture.  A 512 thickness and 850mb temps of -12 on Tuesday morning.  That’s an arctic airmass that took a very short trip over the Pacific!  It only runs to 84 hours, but I sure wonder what it would look like at 96 and 108 hours?  Interesting that this model is noticeably colder than the GFS and ECWMF during this period.  On the other hand, the GFS has been solid for about 6 runs now, showing a surface low coming up against the coastline…it has moved slightly farther south today, but the most recent run (00z) was exactly the same as 2 runs back on low placement.  This isn’t quite far enough south to give us a snowstorm Tuesday night in Portland though so I sure didn’t put that in the forecast.  Once again, note the WRF-GFS shows no snow in the lowlands Tuesday morning through Wednesday morning south of Longview.

Right now all models have a warmup Wednesday and beyond with deep surface lows passing quite close to us…it’s going to be a wild 7 days worth of weather action!

Speaking of…does anyone like THIS?

Is that a windy Friday morning???

Chief Meteorologist Mark Nelsen

Early Friday Evening Snow Update

January 13, 2012

Here’s a quick update without much meteorological talk, I’ll do that later after the rest of the 00z models come in…

First, it’s probably best to tell you what we DON’T expect this weekend:

  1. A snowstorm in the lowlands
  2. An arctic blast, in fact most of the time we’ll be above freezing the next 5 days
  3. Enough snow to sled on for MOST of us.

So will it snow this weekend? 

Yes, all of us will see snow in the air as cold showers stream inland starting Saturday evening and continuing through Sunday evening.  It’ll be cold enough for it to stick in the night and morning hours.  Since we don’t see a lot of moisture, we expect just a Trace-1″ in the lowest elevations (Portland, Salem, etc…) during that time.  If you live on the hills, you may see a bit more, but no more than 3″ even on the highest hills.  If your neighborhood gets REALLY lucky, a batch of showers could pass over Sunday afternoon or Monday morning and give you 1-2″, but I don’t think that’ll be widespread.

Rain will move in Saturday morning, then change to those colder showers in the afternoon, with plenty of sun breaks in between.  High Saturday and Sunday near 40, low near 32 both mornings.

Over the 3 day MLK Weekend, we expect 15-20″ of all powder snow in the Cascades!

Chief Meteorologist Mark Nelsen