I think I can smell a slow-roasting “forecast bust” as I come into the weather kitchen this evening.  The slow cooker will be working overtime tonight and tomorrow morning…

The National Weather Service and at least one or maybe two other forecasters in town (as of the early evening shows) are calling for at least some sticking snow tomorrow evening down here in the lowest elevations in the city.  I think that’s very unlikely; my reasoning is below. 

Here are the highlights:

1. Rain arrives in the metro area and north Willamette Valley around midday tomorrow, sometime between noon and 2pm.  It should fall as rain with snowflakes POSSIBLY mixed in just about anywhere.  Temperatures peak around 40 and stay there all the way through late tomorrow evening.  I don’t expect a temperature drop back down towards freezing.

2. I don’t expect sticking snowfall anywhere in the metro area; the only POSSIBLE exception could be out around Banks and Vernonia if temps don’t warm too much.  Other than that area; up against the east slopes of the Coast Range, you’ll need to be up around 2,000′ to find sticking snow tomorrow afternoon.  Even the central and eastern Columbia Gorge looks very marginal for snowfall late tomorrow afternoon; I-84 will probably be slushy at worst.

3.  Starting late tomorrow night through Thursday, we’re back in the cold showers and clearing periods pattern; almost exactly what we saw over the weekend.  That means each morning any of us could see snow mixed in with the rain, but sticking snow Wednesday and Thursday morning will probably stay in the hills, closer to 1,000′.

4.  Put this together, and you can see we still don’t see a return to winter (lots of snow or a deep freeze) here in the lowlands of western Oregon or SW Washington.  Just more of the late winter cold showers that occasionally mix with snow.

Now, on to the technical chit-chat:

I wasn’t scheduled to work today, but after seeing the snow talk ramping up, I figured I should work and take some other boring weather day off.  Plus, we have NASCAR on right now so no early shows and plenty of time to check out all the other sources of weather information.   Clearly I had too much spare time today…

We have two separate forecast “snow issues” in the next 3 days.

A. Pre-Frontal steady precipitation from midday tomorrow through tomorrow evening.

This doesn’t look nearly cold enough for snow to me; it doesn’t even look that marginal compared to some past events.  In fact if the NWS Discussion hadn’t mentioned it this morning, I would have just said “40 degree rain” and not even mentioned the snow possibility for tomorrow:

1.  Surface temps are too warm and models don’t show the usual “evaporative cooling dip” when we have a dry airmass and moisture starts moving in (December 29, 2009).

Note the 4km WRF-GFS Meteogram  and our RPM  text output for 1-10pm tomorrow:

2. No mesoscale model shows snow accumulating at the lowest elevations

3. Significant warm advection to a bit above freezing in the 1,000-3,000′ layer.  Note the 1.3km WRF  cross-section.  Not only is the 0 degree (celsius) line heading towards 850mb, but the +5 line lifts above the surface!  That goes along with the meteogram above and our RPM text data above showing we hang right around 40 from midday tomorrow through late evening.

4. No cold and dry air coming through the Gorge to keep chilly air in place.  All I really need to say is “1-2 millibars easterly flow tomorrow and it was 46 degrees at The Dalles today”.

5.  In deference to the “Forest Grove Effect” with an approaching low pressure system and slightly cooler air banking up against the Coast Range, I said we could get some stickage out in places like Banks and Vernonia, but I’m not to encouraged that even that will happen.

B. Cold Post-Frontal Showers late Tomorrow Night through Thursday

This is pretty much the same as what we just went through this past weekend.  The old “showers and clearing periods” pattern.  Most of us at the lowest elevations saw nothing. 

I should say that I am somewhat impressed by Wednesday morning’s precipitation intensity.  This looks similar to what brought us lower than expected snow levels on Saturday morning.  In fact our RPM shows all of 0.3″ snow over Portland at that time (around 7am Wednesday). 

So THIS period appears to be the best chance for snow showers to lower elevations.  The Wednesday morning commute will probably bring some heavy snow showers for all of us, but still, anything other than a brief dusting will remain above the lowest elevations with afternoon temps up into the lower 40s.

If you live in the hills up around 1,000′ or higher, 1-3″ is likely again Wednesday morning and again 1-2″ Wednesday night and Thursday morning.   Shower intensity really backs off Wednesday night too, we saw what happened Sunday morning compared to Saturday, even fewer spots saw a dusting for that reason.  Lots of snow covered roads (again!) for Wednesday and Thursday mornings in the hills.

If you live 1,500′ or higher?  Could be sticking snow anytime after 10pm tomorrow night through Thursday evening, with most of the accumulation Wednesday.  6-10″ at that elevation easily.  Here is the 3 day snowfall forecast  from our RPM model. 

Beyond Thursday, upper level ridging moves overhead through the weekend for significantly warmer 850mb temps, so seasonal March highs in the 50-55 degree range will return.

Here are the 12z GFS  and 12z ECMWF  850mb ensemble charts…huge disagreement on either warmer ridging or more cool troughs in the next 10-14 days.  Look at those lines all over the place, especially on the ECMWF!  We’ll see which way it goes.

Chief Meteorologist Mark Nelsen

73 Responses to The “IT ISN’T GOING TO SNOW TUESDAY” Post

  1. W7ENK says:

    On what would ordinarily be the last day of the month, I finally got my first sub-freezing low temperature of 29.5F for this February. I highly doubt tomorrow morning will do the same, so February 2012 gets 1.

  2. Appears that everything is going as Mark has said. Temps are in the mid-to-upper 30’s in just about all locations and WAA is ocurring now aloft. Have to wait till next winter….

    37.3°…Td 28.2…….Light easterly breeze..

  3. stevied (North Portland) says:

    MM5-NAM this morning showing best chance of snow in PDX is Wed AM and Thurs AM. Tough with southerlies. We’ll see.

    WED AM…

    THUR AM…

  4. AlohaWeather says:

    The rain is already at the coast…. will it start as snow?

    • Alohabb says:

      I am at the coast right now, and its rain. Kinda like a sleet but no snow

    • AlohaWeather says:

      I am at 35 degrees, but most of the Hillsboro-Forest Grove area is in the 31-33 range. It will start as snow for the westside.

  5. Joshua in Lake Oswego says:

    I’m not trying to be a downer, but the temp is raising way too fast. Already up above 34 here.

  6. Pippin says:

    Out here in Cornelius: T 31.8 DP 28.0.. Completely cloudy. ECMWF is still predicting snow for the metro.. Not much but a little this afternoon. The rest of the models say nothing but rain until Wednesday morning where NAM and ECMWF are predicting much colder air than previous runs. Looking like snow showers for Wednesday morning. (4am)

  7. Ryan (Walnut Grove) says:

    I mentioned it on the Facebook page but I’ll mention it here as well….

    This event has a very similar feel to the December 2010 event (I think that is correct) where many mets (including Mark 😉 ) had written off any snow chances. We got just down to about 34 or 35 the night before and the clouds moved in preventing the metro area from heating up much (I think mid 30’s). By the time the moisture arrived it fell as all snow dropping 1-2″ from about 3pm to 8pm before it transitioned back to light rain/rain showers. It made the commute a complete mess.

    I do believe the one big difference is that we will have stronger southerly winds this time around. As I recall the wind was fairly calm during the event I mentioned.

    It’d be nice…. 🙂

    • Ryan says:

      It was December 09 but yea. I’ll believe the strong southerlies when I see them.

    • Mark says:

      A few factors to also consider, would be that took place in December, where the sun is at it’s weakest angle. Nearly March, clouds or no, it’s a different story. I am unsure of the southerly low-level push in ’10, but today a southerly flow seems to be in place. Lastly, it appears there will be not wet bulb effect (again, due to the southerly flow).

      Sorry to be such a downer on this, but I’m just trying to be objective with what the data shows, vs wish-casting, as I too want it to snow. At least we always have hope.

    • Ryan (Walnut Grove) says:

      I don’t believe it will snow much if at all over the next 3 days. Just seems similar to that event.

    • W7ENK says:

      December 29, 2009 started out in the upper teens and low/mid 20s, even at PDX (26).

      Go here:

      1. Product » Preliminary Monthly Climate Data (CF6)
      2. Location » Portland
      3. Timeframe » Archived Data: December 2009
      4. View » [ Go ]

      Dewpoints were in the single digits, there was a considerable cold pool in the Columbia Basin, and there was a decent East wind pulling that cold dry air down the Gorge and into the Portland area. Today’s setup is missing several (if not all?) of those factors. I think it would be safe to say that today is absolutely nothing like 12/29/2009.

  8. W7ENK says:

    Man oh man, they’re really beating the snow drum awfully hard! Did Big Joe Bastardi take on a second job with the Portland Office???

  9. Joshua in Lake Oswego says:

    My temp has gone up above 33 degrees now. It was cooler at this time yesterday and didn’t bottom out until close to 8am. That must mean it’s cloudy out- haven’t looked. Let’s see how much we can limit the daytime heating.

  10. 1.3 km wrf gfs brings 5″ snow Wednesday am to this location. I have s hard time buying it, but at least it’s pretty to look at:

  11. bgb41 says:

    2/27/2012 Oregon (All) Temperature Summary

    High:54 at BROOKINGS( 79 ft) & Tillamook(63 ft)
    Low: 37 at BROOKINGS(79 ft)

    High:14 at HOWARD Mt Howard(8150 ft) & ALAKES Haines(7979 ft)
    Low: -2 at CRANE PRAIRIE (5500 ft ) & ANEROID LAKE #2 (7300 ft )

    Largest Diurnal Change: 36 degrees
    CRANE PRAIRIE (34/-2 ) (5500 ft )

    Heaviest Rainfall:
    0.33″ at DW9210 Bend(3615ft)

  12. alohabb says:

    Been 32 in Aloha for at least 2 hours now. Gonna be a fun drive to Tillamook tomorrow! Why is the other 10 oclock news mentioning skipping work…are we in for feet of snow! Thank God I bought that tub of food for emergencies from Costco! LOL

  13. 225' Tigard says:

    Would love to see the 00z RPM Text Output…

    • Mark Nelsen says:

      It’s here:

      Go down to the pull down menus about halfway down the page. The farthest left menu has the RPM products.

    • 225' Tigard says:

      Thanks! It’s weird. The 00z GFS seems to have a strong east wind gradient until at least 9pm tomorrow while the RPM Text says that the wind will turn southerly by 8am at the latest! How can we explain the difference?

    • Mark Nelsen says:

      You might be reading the GMT time as our local time?

      On that chart, the 0228/12 refers to 4am tomorrow, the 00 is 4pm tomorrow. It turns southerly (on this meteogram) around 10am. I have a feeling it’ll be more like 1pm or later for most of us. But strong southerlies will be blowing up above (1000-3000′) soon after 10am.

    • 225' Tigard says:

      Understood for the winds up above but looking at this 00z GFS I thought I saw east wind at 7pm tomorrow:

      • Ryan says:

        I just think it’s cool that Mark posts things literally minutes before being live on air. That’s what makes this blog so great!

    • Mark Nelsen says:

      That’s a pretty coarse resolution to see details like that. It’s definitely easterly over western Washington but southerly over us. I’d say Portland to Kelso is the “transition” area.
      But, still strong southerlies above regardless since the low is to the west and northwest; they aren’t influenced by the terrain. The mesoscale models give you quite a bit more detail:

      And the cross-section shows the warming and southerlies above:

    • Mark Nelsen says:


      I only have to walk 15 feet, that helps

      • Ryan says:

        Or 0 feet with cell phones these days but still, dedication to the blog is appreciated, love to see you posting often to keep everyone sane!

    • 225' Tigard says:

      Understood. Thanks for the insights.

  14. 300′-400′ down to 32 and dropping a degree per hour! If the low drops into the high-mid 20s then we wont get warmer than 40 tomarrow for sure that means SNOW!!!

  15. snodaze says:

    Oh mark… I feel for ya man…

    You shouldn’t have to defend yourself in times like these… It wasn’t going to sno before…. And it’s not going to sno now…

    Get used to it peeps… It’s over already… Has been for some time now.

    And don’t give me the “I live at 1000 ft. b.s!”… Heat rises.. LOL

    • coastrange says:

      I live at 1000 ft. 🙂 will be interesting to watch how this develops for sure. Hope Mark is right as he often is as I have to go to work at 6PM and go home at 3AM. Fighting heavy weather in the dark is drag. Oh and our average temps at my house are 3-5 degrees colder than those of the Tualatin Valley floor. BTW. so the heat must rise quickly and just pass my house by. 🙂

  16. Andrew (Portland....Sylvan Highlands ~800 feet) says:

    Down to 32 and still dropping like a rock.

  17. g says:

    Not as “refined” as Mark is!

  18. AlohaWeather says:

    I hope you are REALLY wrong Mr.Nelsen.
    I’m sure everyone will see something. The people at the NWS aren’t dumb.

    • stormblown says:

      yes the people at NWS are dumb and useless. They are always wrong and Mark is always more accurate. Statistics like that are fairly easy to keep track of.

  19. chris s says:

    Mark, do you have any rational explanation as to what it is that nws sees and the other tv mets see that always lead them to forecast snow in these situations? It seems they never learn from their mistakes, are they looking at maps, numbers,etc or are they just selling sensationalism? They cant really be that bad at their job can they? 🙂

    • Ryan says:

      The NWS seems to make a strong case for a “lack of morning warming” due to increasing cloud cover before the front.

    • Ryan says:

      But if it does get into the 40’s then it’s off

    • Gonna be a decent south wind. That’s gonna warm it up even with a cloud cover.

    • Mark Nelsen says:

      The NWS definitely needs to be on the careful side of things so they tend to go with worst-case scenarios. I doubt most of them actually expect sticking snow in the city tomorrow even if the special statement implies otherwise…in fact check out the part of the forecast discussion here: SNOW ACCUMULATION NOT EXPECTED AT KPDX…HOWEVER A SNOW/RAIN MIX IS POSSIBLE TUE NIGHT. AREAS TO THE WEST…SUCH AS KHIO…MAY SEE LIGHT SNOW ACCUMULATION TUE AFTERNOON AND NIGHT.

      As for other media, I do know one newspaper has written a few sensational articles this winter. The local ODOT and Portland Transportation crews don’t mind being overwarned…far better than underwarning.

      But then you look at comments from regular people and they have the “crying wolf” problem with frequent “it could snow” reports.

    • Ben….it is Hillsboro I think

  20. Ryan says:

    Mark wasn’t completely right on the January storm. He didn’t see the 2 inch widespread accumulation on the night of the 17th…so while it may not be a snowstorm, it could still be something. And as we saw in December 2009, those afternoon commute forecasts can be tricky! 😉

    • stormblown says:

      Mark was as dead on as you can be on that storm Ryan. Jesus you are one anal guy. He said exactly what was going to happen that night. He basically said 2 in . were possible so how was he wrong if it was on the higher end?

  21. Marc (East Vancouver) says:

    Zaffino said most likely just a trace; it’s important to warn people in case of the worst case scenario.

  22. 225' Tigard says:

    The NAM and the GFS both agreeing on the Low coming a bit further south. I still agree with Mark’s call but this does create a bit more of an east wind gradient.

  23. PDX Weather Nut says:

    It’ll be yet another in a long line of blown snow forecasts by the NWS here. 😦 They’ve become like the boy who cries wolf far too many times.


  25. g says:

    Sorry Andrew, ain’t going to happen

  26. Muxpux (Castle Rock 175') says:

    We’ve been having pretty good luck up here this winter. I’m not writing this off quite yet.

  27. Yep. Glad to see I wasn’t all washed up… 😉

  28. Anton C says:

    I simultaneously hate you and admire you right now, Mark.

  29. Andrew (Portland....Sylvan Highlands ~800 feet) says:

    KGW calling for snow starting by 1pm tomorrow at sea level…

    “Zaffino said snow could begin to fall between 1 p.m. and 3 p.m. Tuesday, with up to an inch possible on the valley floor. Up to three inches of snow could accumulate at elevations between 500 to 1,000 feet later Tuesday, with even more snow at higher elevations.
    “The key is the timing,” Zaffino explained. “We could get snow during the afternoon commute, which could be an issue. It will probably begin with a little snow in the valleys Tuesday afternoon and then will turn into more of the rain/snow mix that we’re used to.”
    Zaffino added that conditions in the Oregon Cascades could be “epic” all week for skiers and snowboarders at area resorts.”

  30. Ben T. says:

    I sure hope you are wrong.

  31. EY (Oak Grove 200') says:

    Honestly, I’d like to see something… But I’m starting to enter my “Spring” mode. I don’t want another dreary, depressing, damp, cold, etc. March like we had last year. I’d like to see some seasonal warmth next month, even if it’s only a few days… Not reaching 60 at PDX until the 31st is terrible in my opinion.

    For the short term? It’d be awesome to see a little bit of snowfall. But eh, at this point, I’d much rather see a sunny and 55+ day than a flirtation with snow.

    All I know is it’s definitely cold out there so hey, could be surprised like we were on Saturday.

    • I have to agree with you. Spring mode on my property. Bulbs coming up and plants putting out leaves. Another spring like last year would be depressing. It was very hard on my orchard…pollination was not good and fruit yield low. Flowering plants took for ever to bloom and my hydrangea suffered horribly from zaps of frost. I think it finally put on a few blooms in September, just in time for the weather to change. Although I enjoyed seeing the snow fall over the weekend….the sunshine was pretty darned nice today too!

  32. Wendy-Silverlake, Wa says:

    What’s going on with the wind? NOAA mentions quite gusty winds. Where is the low coming in at? (For tomorrow evening/Wednesday). Since we shouldn’t believe the 500 ft levels they are predicting, is there still going to be winds? I’d rather have a good windstorm (not destructive of course) than a snowstorm any day!!

  33. W7ENK says:

    Are you sure? How sure are you? Scale of 1 to 10…


  34. Andrew (Portland....Sylvan Highlands ~800 feet) says:

    Thanks for the update Mark. Already down to 35 here this evening and dropping like a rock, likely going to be colder tonight.

  35. pappoose in scappoose says:

    I really like a brief dusting!

  36. EY (Oak Grove 200') says:


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