Quick Snow Update

Here are my latest percentages…


As you can see, we’re not real excited about the chance for sticking snow here at the lowest elevations the next few days.  Mainly due to lack of moisture.  It sure looks cold enough from late Wednesday night through early Saturday, but this “event” looks even weaker than that light snowfall some areas saw just before Christmas.

9:45pm Update…

There may be some confusion on those numbers above, those percentages are all “stand-alone” numbers.  I figure a 10% chance of a snow day for schools in the metro area, about a 30% chance of enough snow to affect the commute Thursday morning or evening, and a 50/50 chance of any of us in the lowest elevations around the Portland/Vancouver metro area seeing a dusting.  You need more than a dusting to have any affect on the commute, thus a lower chance.

That graphic is specifically for the Portland area. For those of you in Salem and farther south, I’d give it about a 70% chance of a dusting and 50% chance of AM or PM commute issues.  I see some models are spinning up a weak surface low pressure area and dropping it into western Oregon during the morning Thursday.  This isn’t a new development, models have been consistently pointing more moisture into SW Oregon.  Here’s the WRF-GFS 24 hour precipitation from 4am Thursday to 4am Friday.  There’s enough precipitation there to give at least a dusting to the central/southern Valley.  This could be a situation where a cluster of showers moves into the Valley and drops 1-3″ from Salem southward Thursday morning and the metro area stays dry…we’ll see.  Soundings appear cold enough too:


I lowered our 7 Day forecast temps a bit based on a minor change the past few runs…the upper level ridge is going to be a bit closer to us than what we were looking at 24 hours ago (slightly closer).  The effect is a bit more offshore flow at times, although week.  The ridge is not in a position to give us any sort of strong east wind (or even much) like we saw last week, but a little more continental/drier air means lower nighttime temps and daytime highs only around 40 or so.

I’m also ignoring the 00z GFS deciding to ram an upper-level shortwave right through the ridge on Saturday and down into California.  That was a weird development and leaves us dry with chilly offshore flow.  The NAM still has some very light rain/snow over us Saturday with the freezing level around 2,000′, although we are on the edge of the precip area.  Our RPM only goes through Friday evening.  The 00z GEM is similar to the NAM.  Other than that, it appears we are heading into a long-term ridgy period again.  The 00z GFS has no rainfall for a 9-10 day period starting Thursday evening!

Chief Meteorologist Mark Nelsen

222 Responses to Quick Snow Update

  1. Jane Ott says:

    I live on the coast and sometimes we get frost when the temp is above freezing. What causes this?

    • pappoose in scappoose says:

      From the Washington State Department of Transportation Road Weather Project:

      2. The temperatures at official weather observing sites generally provide air temperatures at approximately 5 feet, at which height temperatures are generally warmer than road surface temperatures on cold, clear nights. Thus, if air temperatures drop below approximately 37F icing conditions may already be occurring at the surface!

    • W7ENK says:

      That would be due to evaporativtativational (evaporative) cooling. 😉

  2. paulbeugene says:

    If the low tracks to the west of you but not too far…yes

  3. paulbeugene says:

    S E A H A W K S W I

    Forecast for Saturday night and Sunday:

    A period of snow down to valley floor Saturday evening/night with snow showers on Sunday, with snow level at 1500′ to the west of the low/disturbance and probably below 500′ to the east of the low track. Some lucky souls just east of the low track will get 2-4 inches…others to the west will get nothing, and those to the east will get a dusting.

    Regardless of the low track, the Seahawks will win.

    • paulbeugene says:

      Anyone within 50-80 miles of the low to east should get some snow…I mean…but the moisture will be best for a relatively narrow area. I the low tracks right along the coastline that would be ideal from a moisture standpoint.

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