Snow Thoughts For The Weekend

For those of you just checking in and not wanting much detail, here’s what I have for you:

  1. No dramatic changes in thinking since last night at this time
  2. Timing of the arrival of colder air (and rain) has moved up.  Precipitation arrives Saturday afternoon as rain.
  3. By Sunday morning, and continuing through Monday midday or so, anything that falls out of the sky, even at the lowest elevations, will be in the form of snow.  Everyone will at least see snow in the air Sunday and/or Monday.
  4. Will there be “sleddable snow” in Portland?  I’d give it a 40% chance right in the city; just slightly lower confidence than last night.  My reasoning is below.
  5. Up on the higher hills (near and above 1,000′)?  Near 100% chance of 1″ or more Sunday-Monday.
  6. Traffic issues in the metro area?  Probably only on the hills Sunday morning and again Monday morning.  I doubt this will impact main roads/highways, but that could change.

Okay, now on to the details:

Gusty east wind continues this evening, with peak gusts earlier today in the 30-40 mph in many exposed spots around the metro area.  Vista House wind picked up this evening with a peak gust of 80 mph; safe to say it gusted to 100 mph “on the railing”.  Overnight the wind should retreat mainly to areas east of I-205 and near/south of the Columbia River.

Did you notice the extremely dry air today?  In spots (Clark County and western Washington County) where the wind has dropped off, we’ve seen 9pm temps already down in the mid 20s!  Lots of upper teens coming up later tonight as the wind keeps dying down away from the Gorge.

More of the same, but less wind, the next 2 days.

Obvious change in the past 24 hours is the timing has been moved forward.  The main cold front arrives late Saturday afternoon now.  Much colder atmosphere behind the front drops the snow level very low overnight Saturday night.  Expect a snowy Coast Range well before daybreak Sunday.

From Sunday morning to Monday afternoon then we have the classic (annoying) setup of cold showers streaming onshore from the west and northwest.  At the same time, a southerly breeze is blowing up the western valleys.  850 mb. temps drop to around -7 to -9 C.  That’s right at the threshold for snow sticking to the Valley floor.  So IF we get a good cluster of showers, there’s no reason anyone couldn’t see some accumulation of snow.  But moisture seems to be lacking during this whole period.  It’s a “showers and sunbreaks” sort of pattern.  That’s the main reason I’m not too excited that we’ll see significant lowland snow.  Note the 24 hour precipitation forecast from the WRF-GFS from Sunday morning to Monday morning.  It often appears to be shifted slightly west of reality due to the contouring.  So assume that whole dry area, rain-shadowed by the Coast Range, is running down the middle of the valley.  This model only shows a trace to .15″ over the driest part of the valley:

Then note the corresponding snowfall forecast:
So technically the WRF-GFS shows a dusting or less for most of the lowest elevations, much better chance of an inch or two once you get up in the higher hills.

Beyond that, the snow level gradually rises Monday evening into Tuesday.  You can see this nicely in the 00z GFS 850 mb. ensemble chart that just came out a couple minutes ago:

Great agreement (best we’ve seen in a few days) on the pattern through Tuesday for sure, then a few members have a shot of cooler air on Wednesday, maybe those are still trying to send a surface low right overhead on Wednesday, pulling in the cooler air.  Regardless, the trend in the 00z GFS is definitely milder the rest of next week, but lots of rain and tons of mountain snow.

I should point out that earlier GFS runs and their ensembles today had the whole pattern shifted a bit farther south, for a more marginal snow situation Tuesday-Wednesday.  It’ll be interesting to see if the 00z ECMWF shifts things a bit farther north as well.

To sum it up, it’s quite possible we get nothing sticking officially here in Portland Sunday-Monday, but if we get lucky some cluster of showers will form and drop a quick couple of inches.

Chief Meteorologist Mark Nelsen

176 Responses to Snow Thoughts For The Weekend

  1. flurball says:

    hour 138 850 MB winds at 103. Don’t recall last time I have seen something over 100

  2. When was the last time we saw that forecast over PDX???

    Check out hour 138 and 180 on the 0z GFS

    http://wxweb.meteostar.com/sample/sample.shtml?text=KTTD

    It’s strange how at the surface the winds are so much lighter.

  3. Get out the life boats sailors, cuz once we get thru the shot of marginal snow we go into the deluge. Arrgghh…

  4. Lots of high clouds moving overhead and quite a few to come. This could (and already is) hindering radiational cooling.

    http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?ir4km_enhanced+12

    31.2 here.

    Last night it was 28 at the same time.

  5. flurball says:

    0Z battle plans appear to want the approaching low next Wed to storm the beach at Aberdeen and capture the Kurt Cobain memorial statue. Need a mole to slip them a menu from Moe’s in Newport to change the battle plans to create a D-Day celebration in PDX.

  6. Brad says:

    Wow. WRF-GFS looks cold enough for snow at 51 hr.

  7. flurball says:

    torpedo port side 45 degrees

  8. WhiteEagle - Garden Home/SW Portland says:

    Stay on target…stay on target…

    • WhiteEagle - Garden Home/SW Portland says:

      Tue afternoon: 00z says mix rain/snow quickly changing to snow…or starting off as snow. 1-2 inches by commute time.

    • WhiteEagle - Garden Home/SW Portland says:

      Southerly flow not opening up yet by 03z Wed. We’re up to 2-4 inches…but warm air is coming fast.

    • WhiteEagle - Garden Home/SW Portland says:

      Precip is picking up big time during the evening…just in time to change over to rain by midnight. 2-6 inches of beautiful snow quickly turns to slop as a windstorm begins to take shape along the coast.

    • WhiteEagle - Garden Home/SW Portland says:

      Wednesday: STRONG southerly gradients throughout. This is turning into one heck of a heavy rain and wind storm…possibly windy for the valley as well. I’m liking this…

    • WhiteEagle - Garden Home/SW Portland says:

      7-9mb gradient EUG-PDX Wed. About 20mb from Brookings to Astoria…

    • Josh Smith (South Salem 400' ) says:

      where do we go to get this info at?

    • WhiteEagle - Garden Home/SW Portland says:

      It’s Piña Colada time for the rest of the week… Some impressive rain along the Oregon and NorCal coast, making up for lost La Niña time.

    • WhiteEagle - Garden Home/SW Portland says:

      Josh, the raw model data can be found at NOAA’s site here

      http://mag.ncep.noaa.gov/

    • Josh Smith (South Salem 400' ) says:

      Thanks WhiteEagle,

      so being a weather manic, i really dont know how to read all the maps that well , i was wondering what you think or others think of the chances Salem has in this process??? alot of people say that we need to have the low come in around newport, and temps be at -8 C. is that right? if that is right, hows this setup looking for salem? anyone help me out? thanks

    • WhiteEagle - Garden Home/SW Portland says:

      -8 is good for onshore flow situations, but you don’t necessarily need that if the low comes up from under you. Hence the Newport rule, which is probably pretty good for Salem. I may even say Florence. I think you’ll see some snow showers Sat evening thru Tue, maybe rain showers too. IF this model is right (which it probably isn’t, they often change), I’d say 1-3 inches in Salem before it turns to rain and a windy day Wed.

  9. WhiteEagle - Garden Home/SW Portland says:

    This is nice out to 93h…

  10. Brad says:

    00z – 54 hr …looks good so far. Colder than 18z.

  11. Gonna be at Crestview Manor, that can’t be too far from Mark’s house. We are all praying for some awesome sledding times Sunday…..

  12. Steve in Salem says:

    Everyone buckled up and ready for the ride. Please keep your arms and legs inside at all times.

  13. Brad says:

    00z is going to be huge – one way or the other….

  14. Tigard 225' says:

    00z NAM is colder and more moist SAT thru MON to my layman eye.

  15. If anyone is interested there’s an awesome Weather group on Facebook that includes Mark Nelsen and Steve Pierce. It has lots of info and programs for the average weather geek 🙂
    https://www.facebook.com/groups/158533057538771/

  16. o.c.paul says:

    Forecast-Rockford, IL (my hometown)
    Currently snow 12 degrees 4-8 inches
    Tomorrow- 18 degrees mostly cloudy, breezy, colder
    Saturday- 26 degrees cloudy, snow showers
    ROADTRIP!!!!!!!!!!!!!!!

  17. Mountain Man says:

    18z coming around to the Euro for snow through Tuesday and possibly in the hills to Wednesday morning due to hard steady precipitation as the air mass starts to warm. Will be interesting to see if the 00z continues with the Euro giving us another good run tonight. Looks good for lots of snow for me way up in the foot hills either way though.

  18. g says:

    Bob can be whatever he wants. Leave em alone.

  19. alohabb says:

    Ha! New neighbors pressure washing driveway and sidewalk! It wont evaporate soon so the dirve.sidewalk and street are gonna be real slippery! That’ll be fun to watch.

  20. AlohaWeather says:

    Check the 7 day forecast…Looks like someone does not know the 7 days of the week.

    • Bob says:

      Yeah I saw that, looks like Mark thinks the GFS scenario will playout and not the ECMWF.

    • royalpain83 says:

      Actually, today being Thursday, having FRIDAY next on the forecast followed by the next 6 days makes perfect sense…That’s how it has always been done. So, If today was Monday, the 7 day forecast would read; Tuesday-Monday. Got it?

  21. Mark Reschke says:

    Our Government Weather team seem to be getting it about right. After the cold surge, some snow, Tuesday looks to make for a quick transition into wet and warm the remainder of the long-range.

    That would be quite a bummer, but the GFS and ECMWF are bearing some form of solution to that effect.

    However, our friendly Canadian model throws the low into NoCal, leaving us dry and cold. I always loved those Canadians for a reason!…

  22. W7ENK says:

    SP’s latest press release, as of 8 minutes ago.

    http://www.piercevideo.com/weather.shtml

    I still think there’s a “Bob” connection here. 😉

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