Wednesday’s Storm: Very Low Confidence So Far

9:30pm Monday…

Forecasting specific totals for Wednesday’s event would be a very risky endeavor this evening.  This is the one time I think we don’t have a good idea what’s going to happen over the metro area just 48 hours ahead of time.  We need to give it more time and several more model runs to see if they come together and tighten up their forecasts.  This is quite similar to what happened in early February 2014.  Just two days ago it appeared that Wednesday’s system would be totally missing us to the south.   Then in the past two days models have trended north and wetter over us.  But again this evening there has been a southward trend again; several show LITTLE OR NO PRECIPITATION OVER US WEDNESDAY!  Take a look at this compilation of the evening runs.


I made a rough conversion of rain to snow, assuming a 1 to 10 ratio.  On average 1″ of rain can give you 10″ of snow.  Wetter snow a bit less, drier snow more for each inch of rain.  Do you see why it would be nuts to forecast a snow total right now?  You can see the closest approach of the precipitation at 4pm Wednesday on our RPM model:


I do have high confidence with three points

  1. Central Oregon and the Central/Southern Oregon Cascades are going to get hammered!  That .87″ at Bend could give them 8-10″ snow since cold northerly flow will be pushing south into that part of the state.
  2. IF we get precipitation (likely in the form of snow) then it would arrive Wednesday afternoon at some point.
  3. Wednesday will likely be a dry day in most of Western Washington.

Stay tuned, I GUARANTEE there will be more twists and turns the next 24 hours!

Chief Meteorologist Mark Nelsen


28 Responses to Wednesday’s Storm: Very Low Confidence So Far

  1. paulbeugene says:

    All in all still very much up in the air as to what will happen with snow tomorrow. NAM farther S, Gfs a bit more moisture in central and north willamette valley. GEM model shows a few inches over central and north valley. Will await Euro run.

  2. Anonymous says:

    All in all still very much up in the air as to what will happen with snow tomorrow. NAM farther S, Gfs a bit more moisture in central and north willamette valley. GEM model shows a few inches over central and north valley. Will await Euro run.

  3. pappoose in scappoose says:

    There comes a time when you just gotta ask The Magic 8 Ball!

  4. Shawn Lietz says:

    Not as much of a weather geek as some here, but am a fan of all things weather related, think they are fairly cool. Few questions though. One, just how many models does Mark look at? Two, why cant they seem to agree on anything past 24 hours?

    • marinersfan85 says:

      There is 4 models. All run between 2 and 4 times a day.

      As to why there is so much disagreement? Your guess is as good as anyone’s.

    • bobob says:

      There are Many weather models to look at. The GFS, The Euro and the GEM are the main 3 used

  5. Washougal1100ft says:

    Let’s hope that low move just 100 miles north and we will be berried in snow! Could be Amazing or just cold and sunny ☀️! Models move north and south all the time 24hrs still to go lots can happen! I remember a few years back we were in the bulls eye the whole time and last minute they shifted south and we got nothing so maybe this will be the make up for that! Think optimistic everyone!

  6. JohnD says:

    Really hope I am wrong but it seems like things are trending dry this far north and west (e.g. Portland). Soooooo hard for a bullseye here. The same old story: Cold enough but no precip. Or plenty of precip. but too warm.

    I know we can’t know with certainty for another 12 hours or so. Hopefully we do get at least SOMETHING! But the big goods look south and east. Things could change.

    Have vowed to not check media again until after work tonight! I’ll be ready then to either cry in my beer–or–hopefully–celebrate!

    • JERAT416 says:

      Sometimes it’s too far north too. I remember a few years back it was raining and cold air was coming from our north. It was so slow coming that by the time it got here, we just got a trace of snow before the moisture was gone. Yet Seattle got a bunch of snow

  7. Jake-(Gresham) says:

    Next 5 day snow forecast (GFS 00z):

  8. Jake-(Gresham) says:

    Special Statement
    Issued: 3:59 AM PST Dec. 13, 2016 – National Weather Service

    … Low elevation snow and ice possible in much of southwest
    Washington and northwest Oregon Wednesday and Wednesday night…

    A winter storm system will impact northwest Oregon and southwest
    Washington Wednesday and Wednesday night. Moisture will spread
    north during the day Wednesday… then move off to the east later
    Wednesday night and early Thursday.

    There is still a lot of uncertainty about precipitation type and
    amounts. At this time… the most likely solution is for some light
    snow in the northwest portions of the area mainly Wednesday
    afternoon and evening. Farther south will probably see period…
    possibly brief… of snow before mixing with freezing rain and
    sleet. Heavier precipitation amounts will tend to be in the
    southeast part of our forecast area.

    Coastal sections may see a light mix of rain or snow though
    southern sections near Newport could see mostly rain.

    The models are indicating that the precipitation may change back
    to mostly snow later Wednesday night before decreasing.

    While this is the most likely solution… there is still some
    model uncertainty… therefore a lot can change between now and
    then. Stay tuned to weather.Gov/Portland for the latest forecast

    • Scooter says:

      Wow, pretty far fetched if you ask me, in my 65 trips around the sun I have only seen on two or three occasions that we had high temperatures in the low 20’s and those times the lows at night were down around zero degrees. Just aint goin’ to happen.

  9. Gregg in Bend, formerly Troutdale Gregg says:

    Thanks for the update Mark. Based on what we saw in Bend last Thursday, 8-11″ and looking at what this storm could do, I’m thinking we see at least a foot or more in Bend.

  10. paulbeugene says:

    Won’t know until tomorrow evening what’s likely to happen. Gfs ensembles and Euro support idea that precip mostly confined to Oregon and points south. There will be winners and losers. I think Albany N to Woodburn may be sweet spot.

    • Benjamin (West Salem) says:

      I hope you’re right 🙂 I think you guys should be able to score some too unless that warm air aloft turns it to freezing rain.

    • Jake-(Gresham) says:

      Thanks for your thoughts and I’d be down for that. If the storm goes South of PDX to a greater extent where we hardly get anything. Totally could setup the valley for a recursion event (i.e. another Winter event) all the way into Christmas.

    • B1900Pilot says:

      Thanks Paul, looking forward to what you have to say this evening.

  11. Benjamin (West Salem) says:

    Like usual I think it’s going to come down to the GOLU model.

  12. Garron 1/3 of a mile from Hillsboro Airport says:

    Looks like it would be a great time for a road trip and hotel stay in Bend! Hoping that low strengthens, and curves a bit north! C’mon, just 100 miles would make ALL the difference. All is not lost on this storm though, it looks to stay rather interesting into Christmas! Mark, you have your work cut out for you…

  13. marinersfan85 says:

    Throw a dart and go with that forcast!

  14. Taylor (Happy Valley) says:

    Why have the weather models been so inconsistent lately? They need to get their act together. I’m hoping for some snow. That snow/ice event didn’t cut it for me.

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