Snow Likely Tuesday Night Metro Area

January 9, 2017

11pm…

Confidence has grown that we’ll see at the least a coating of white (1″) in most of the metro area Tuesday night and Wednesday and possibly as much as 4″.

All evening models are in and they all show something similar.

  1. The main precipitation shield from the storm moving through southern Oregon tomorrow doesn’t make it to the metro area.
  2. Instead we get a widespread area of light snow that develops tomorrow evening through much of Wednesday over much of NW Oregon, including the metro area and Salem/Albany.  This is generated by moisture lifting up under an upper-level low.  The low sits over us through much of Wednesday

The WRF-GFS, NAM, GFS, & ECMWF all show the same general idea.   They also generally show heaviest totals west metro as opposed to east.  ECMWF wasn’t as particular though showing that east-west divide.  Check out the precipitation forecast for the 24 hours ending Wednesday at 4pm:

ecmwf_precip_24_portland_9

And the accompanying snow forecast, noting that in the first 6+ hours it might be too warm for sticking snow in Salem/Albany:

ecmwf_snow_24_portland_9

So the 1-4″ forecast seems good for now, at least until the 12z runs come in.  I’ll be blogging again in the morning once I wake up and get going.

For now I think a major point is that we DO NOT EXPECT issues for the evening commute Tuesday.

This all happens later in the evening and into Wednesday.  Obviously if we do get the snow then Wednesday is a different story.

Chief Meteorologist Mark Nelsen


Another Tough Snow Forecast; Tuesday Night & Wednesday

January 9, 2017

3pm Monday…

The last of the cold temps from the east wind are (temporarily) gone in the metro area and we’ve moved into the pattern I mentioned last night…low level rain showers and snow showers in the hills.  At times the snow has been sticking down close to sea level in the heaviest showers, but the showers will be tapering off this evening.  So everything looks clear for the evening commute.

There is one minor challenge and then one big one headache forecasting the next 48 hours.

First…the easier one:

A weak system snuggles right up against the north Oregon and south Washington coastline tonight.  There is a surface low pressure system that’ll move onshore right around Astoria late.  Take a look at our RPM model for

rpm_cloud_snow

That causes wind to go calm or light easterly (we lose the mild onshore flow) anywhere north of Portland.  Combine that with the leftover cool airmass overhead and it’s possible we see sticking snow well below the 2,000′ models suggest.  As a result:

  1. Later tonight snow may stick down close to sea level north and west of a Hillsboro to Vancouver line.  That means there could be a dusting or even a bit more from St. Helens to Kalama to Kelso.  Maybe Battle Ground too.  Not a big snow-producer, but it’s a tough call.
  2. Most likely any sticking snow will be confined to the top of the West Hills or higher in the metro area.  East of Multnomah Falls in the Gorge it should fall as snow too due to a light easterly flow continuing over there.

Beyond that not much happens tomorrow during the daylight hours, then the big forecast challenge arrives.

Another big storm will be moving right across the middle of Oregon, taking a path very similar to our last snow event in mid-December.  That was the one with the Traffi-Pocalypse on the 14th.  Remember that afternoon?  The central/southern part of the state is going to get hammered once again with a big snowstorm.  That includes Bend, Burns, Madras, Lakeview, Klamath Falls.

The big issue, just as in the previous storm, is HOW FAR NORTH DOES THE PRECIPITATION GO?  Just about all models cut off the precip somewhere around a Tillamook to Clark County line, with rain to snow developing south of that line and mainly dry to the north.

TUESDAY/WEDNESDAY HIGHLIGHTS

  • Most of the daylight hours Tuesday will be dry
  • In the afternoon the strong & cold east wind will be spreading out of the Gorge again and into the metro area.  Gusts likely exceed 40 mph by evening east metro again…brrr!
  • By sunset (5pm), rain will have begun in Salem and Eugene, spreading north
  • At some point after 6 pm rain should arrive in the metro area, with temperatures a bit above freezing.  At this point the evening commute appears to be fine in the metro area
  • Within a few hours temperatures will go below freezing and rain changes to snow
  • Snow falls through the night tomorrow night and ends Wednesday AM.  Accompanied by strong east wind east metro, expect blowing and drifting late into the night.
  • 1-4″ is possible in the metro area, likely most south, lighter north <<< THIS FORECAST WILL LIKELY CHANGE THE NEXT 18 HOURS
  • If this occurs, Wednesday will be a snow day for the kids and lots of workers too.
  • Wednesday the flurries end and we go cold/sunny the 2nd half of the week; just like after last week’s snow.  Snow/ice will gradually work/melt off the roads.

We’re still 30 hours away and have 2 more model runs to firm up that snow total a bit.  A couple of models keep us totally dry with all the action staying south.  I think that’s unlikely, thus the 1-4” snow forecast.  More info this evening and a final look mid-morning tomorrow should give us a much better idea of exactly what to expect.

COMMUTERS/SCHOOL ADMINISTRATORS

Even though the Tuesday evening commute looks fine in Portland/Vancouver/Salem, pay very close attention to the forecast in case for some reason the arrival of precip and cooling (rain to snow) speeds up.  Imagine if everything speeds up 5 hours and we get rain by 2pm and freezing at 5pm.  That would be bad…so pay attention.  Schools should be just fine tomorrow too since no modeling/forecast shows anything interesting in the 2-4pm timeframe.




This situation is very similar to the December 14th storm…a big precip producer moving across mainly the southern portion of the state with the NW tip of Oregon (and metro area) at the northern edge of the precip band.  A few things stick out on the maps/models.  First, several models bring a 2nd weak low or at least surge of moisture farther north right over us late tomorrow evening and during the night.  The ECMWF is most insistent on this and it’s thinking 2-5″ of snow, the GEM is similar and very white too.  Both these models give a real snowstorm for most of the metro area.

ecm_snow

On the flip side the NAM is keeping just about all precip to our south.  Well, it IS the NAM…moving on.  I’m pretty confident that we’ll see at least SOME snow, but luckily as mentioned above we do have a couple more model runs to fine tune the forecast.  It also helps that just about all the event is happening when most people are home…after the evening commute and before the morning drive.  I’m so glad that this isn’t predicted to begin at noon and cool down to freezing around 5pm.  It’s starting later and we’ll have a relatively “warm” airmass as the event begins.  Of course there is the outside chance that we somehow get freezing rain to start, but I think that’s unlikely because the upper-level airmass will cool first before the lowest levels freeze up.

One BIG thing to remember from that December 14th storm.  Remember the precip was supposed to move no farther north than Tillamook to Clark County?  Instead snow fell all the way to Astoria and Longview!  A change of 50 miles will make a huge difference tomorrow night!

kitty_windowlicker

Keep those kitties watching out the window…yes, we’ve found our first window-licker-wishcasting cat.  Sign me up!  Thanks to Sara for the pic.

More later…Chief Meteorologist Mark Nelsen