A Challenging Forecast

For those of you just wanting the forecast details tonight, here are the highlights:

1. Ice all over the place tonight as temps have dropped to or below freezing with some areas of wet roads from the earlier snow showers.  This continues overnight, and we may add a dusting of snow over the top of that for the morning commute.  Expect a none to 1/2″ additional snowfall in the late night and very early morning hours.

2. Tomorrow we gradually thaw out with snow showers here and there, picking up some in the evening.  After noon tomorrow, most (or all) sticking snow should be confined to the hills and above through Tuesday.  By that I mean once we get past noon tomorrow, the vast majority of metro area roads will be in the clear through Tuesday evening at least.

3.  Snow showers turn to mixed showers, and then mainly rain showers Tuesday.  On Tuesday the sticking snow level should be around 1,000′ in the morning, and up to around 2,000′ by evening.

4.  Winter Storm Watch is up for the eastern Columbia River Gorge.  Technically it’s only for The Dalles east, but that’s because that forecast area comes from the Pendleton NWS.  Cascade Locks and Hood River are likely to see even more snow than that (6-12″) but are under the Portland NWS forecast area.  They haven’t issued any watches or warnings yet.  That happens once in awhile.  Either way, I’m increasingly confident there could be a heavy snowfall in the central/eastern Gorge Tuesday night and Wednesday.  Even our warmest model shows it just barely cold enough.

5.  Significant snow is also possible Tuesday night-Wednesday north of Longview in SW Washington.  Too early for amounts, but at least 2-4″

Now on to the details…I had lots of time (probably too much time) to look at just about every piece of meteorological data I could find this evening.  My brain is fried, but here goes…

TONIGHT:  Our RPM model (the only one doing so) keeps insisting a batch of showers (the one over the North Coast right now?) moves eastward into the metro area before sunrise with a Trace-1″ accumulation.  It’s done that for several runs.  That’s why I added the possibility for the metro area.

MONDAY/MONDAY NIGHT:  The coldest atmosphere of this whole event is over us now, and we gradually begin to warm overhead, especially after 4pm tomorrow.  All models (even the NAM) show moderate southerly wind developing not only overhead but at the surface as well later tomorrow.  It goes all night tomorrow night and into Tuesday morning.  I noticed the 25kts. of that onshore flow on the WRF-GFS just overhead, and our RPM goes breezy as well.  This is due to a fresh batch of arctic air spinning up a surface low off Vancouver Island.  Lowering pressures to the north induce the south/southwest wind here.  Due to this, I feel the snow level tomorrow night lifts off the Valley floor (as you see in the forecast).  I doubt there will be any freezing Monday night.  This shows up well in cross sections as the zero degree line gradually rises.  And the image below shows little or no sticking snow from now through Tuesday afternoon in the lowlands.

TUESDAY:  More of the same, frequent showers may just turn to mostly cloudy with light rain at times as the atmosphere overhead continues to GRADUALLY warm.  GFS, RPM, WRF-GFS, and ECMWF are all too warm for sticking snow here with a decent onshore flow.  They all show 850mb temps between -4 and -7.  Yes, I know the NAM has -7 to -8, but that’ significantly warmer than the -10 to -12 it was showing just 24 hours ago.   But several inches of fresh snow above 1,000′, especially early.

TUESDAY NIGHT & WEDNESDAY:  This is where things become a MAJOR pain.  That stupid NAM!  It has a deep surface low tracking into Central Oregon, pulling strong easterly and northerly flow right down over us at the same time plenty of precipitation arrives.  Almost a perfect snowstorm here in Portland and Salem too; huge in the Columbia River Gorge.  But the ol’ GFS comes in with the exact same low pressure movement during the same period, bringing a surface low to the Washington Coast.  It seems SLIGHTLY farther south, but it doesn’t matter for the western valleys; warm air floods in during this period.  Even this “warm” GFS appears it’s just far enough south with the low center for 32 degree temps all the way down to the surface in the central/eastern Gorge, so I pulled the trigger on that one and will make a graphic for it.

For those of you agonizing over the thought “how models can be so far apart?”; keep in mind that it’s only one surface low location that’s maybe 150 miles off from one model to another.  Compare the upper-level patterns on those models and they are only slightly different.  It just so happens that we live in a spot where the actual weather can be far different based on these two different solutions.  Hey, it’s only 1 hour until the 00z ECMWF!!!

Chief Meteorologist Mark Nelsen

129 Responses to A Challenging Forecast

  1. Josh (Gresham) says:

    ‎18z GFS at hour 48… WOW

  2. philinforestgrove says:

    Seems like 150 miles is a large swath of uncertainty for landfalls of L’s and makes a huge difference in our weather. Observation of this blog is that the L’s almost always track further north than everyone anticipates. How’s this one shaping up?

  3. Jake-(Gresham) says:

    I have to remind myself that whatever the models say is not reality. I believe in this kind of situation where such a small variation has such a significant impact on what happens that the best thing to do is wait the good old fashioned way and watch the radar.

  4. David B says:

    NWS has issued Winter Storm Watches for both Seattle and Portland areas this morning. SEA for tonight through Wednesday, PDX for Tuesday night through Wednesday. Looks like those of you passed over in the snow department so far shouldn’t give up hope quite yet.

    • Mark Reschke says:

      Rod Hill just gave his daily video update (9:45am). He sees snow showers thru mid-day Tuesday or so, then a cold rain Tuesday night into Wednesday and warming continuing from there.

      Thus, Rod Hill – and Mark Nelson to this point – seem to be pointing to this thing fizzling out. The NOAA seems to still be pointing to a major snow event. Who do you trust?…

    • Ryan (Walnut Grove) says:

      I’m inclined to go with a fizzle event… I suspect there will be lots of weather blog fans ready to jump off a bridge.

  5. snowlover says:

    Did Mark just update the 7 day? It looks different….

  6. Muxpux (Castle Rock 175') says:

    Just had a snow shower In longview. We better be under the bullseye!!

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

    I REALLY like that band of precip moving in off the coast!

  8. also some very good material/analysis from Cliff Mass on his blog the past 24 – 36 hours.

  9. I don’t think the valleys will get much, but at 1600′ I am going to get buried.

  10. Jclack says:

    Very interesting AFD posted a few min ago by Portland NWS

    • yes..very good analysis and discussion. pretty much what mark is talking about on this post. a forecasters worst nightmare. which way to go? what to advertise? sounds life nws is going with the ‘middle’ ECMWF solution. they think the GFS and NAM are too far warm and cold respectively and too far apart from each other to take a gamble on either one. Go NAM!!!

      We already have 4.5 inches on the ground here in Gates at 1,000 feet, so I feel we’ve already done pretty well. Wouldn’t it be neat though if the NAM verified?!?!?!?

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

    Mark, a high of 52 for Wednesday? You may be setting yourself up for a major bust.

  12. Kyle says:

    We have a quarter inch of snow with a thin sheet of ice but Dad was able to make it out on time and the Silver Falls School District for the kiddos are on time. They don’t get a snow day. 😦

    It’s funny how everyone except Mark was calling for all this snow which Mark wound up being right again.

    Has there ever been a time where a storm was more severe then Mark forecasted?

  13. Paulbeaverton says:

    Wake up, Mark! 🙂 Has anything indeed changed or is this classic NWS “just to be sure” thinking?

  14. boringlarry says:

    …gotta like this from the early morning AFD from Seattle …


  15. TAGinGresham says:

    Woke up and checked the NWS forecast for Gresham and literally said “What the he&%”. They are predicting 1-2 tonight, 1-2 Tue., 3-5 Tue. night and 1-2 Wed., That’s 5-9 inches! Are they nuts or has something changed?

  16. EmzinTigard says:

    Drove my husband to work in Vancouver.. coming from Tigard. Tigard/Beaverton are by far the snowiest locations I saw. It snowed most of the drive this morning.

  17. Looks like it could indeed be another December 1, 2005 for the NWS (and Zaffino for that matter).

    Patiently awaiting Mark’s thoughts this morning

  18. o.c.paul says:

    Flurries at 200′ in Oregon City. More, more, more…

  19. Brad says:

    A good rule of thumb: Don’t bet against Mark.

  20. Take a trip on Trip Check! Nice pics of snowy roads and towns. Don’t forget to scroll down. The coast looks beautiful in spots too.

  21. Mark Reschke says:

    It has apparently been quite some time since Meteorologists have been this divided with an event only 24 – 48 hrs out. Zaffio sporting up to 4-8 inches of snow, the NOAA pulling towards the same direction (using the ECMWF models to bolster their position), with Mark Nelson seeing a southerly wind making the event a wash-out.

    Go back 5 days and Wednesday’s storm was going to track into northern WA/Vancouver Island region. Then that pesky NAM – the rebel that it is – started getting out-of-line, pushing the low into Oregon.

    I like watching trends, and the trend has been to push this moist low pressure further and further south. Every model has trended this way. That does not mean a Newport landfall, but IMHO it’s looking more favorable for the metro-area to pick up some heavy wet snow Tuesday night, at the least.

    Someone point out the year, but I can recall a New Year where we saw about 4-5 inches of steady light snow falling all day long, with the low tracking into the state around Eugene/Salem?… This seems eerily familiar… Football and snow, gotta love it.

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