Monday PM Update

Will there be enough, or any, snow to go sledding on Wednesday morning here in the lowest elevations?  Seems unlikely right now, I’d give it about a 20% chance fo “sleddable” snow here in the Valley.  It IS a tough forecast the next few days. 

Apparently we’re back to the usual “will the moisture and colder air mix it up just right” game for the first time this season.  In November we had an amazingly cold blast of air come in from the north and northwest…remember how easily we changed to snow and then a hard freeze overnight that Tuesday?  Then a few times this month we’ve had chilly air in place and moisture arrive over the top of it.  Evaporative cooling dropped temps down enough to bring at least the sight of snowflakes into the city with those. 

But this will be the first time this year (I think) that we’ve been close to snow with the cold instability showers behind a cold front.  And those of you who’ve been on the blog for several years know how frustrating it is to get decent showers coming in from the northwest.  Often the Coast Range eats up a good chunk of the moisture.   The biggest issue is that the cold air in this case is travelling over about 2,000 miles of mild Pacific Ocean water before it gets here…really tough to get snow to sea level in these situations for that reason alone.

Not much happening in the next 24 hours as a juicy cold front sits over us.  A 2nd wave renews the rainfall tomorrow afternoon and evening.  Our 18z RPM had shown steady and heavy precipitation lingering with that wave until the middle of the night tomorrow night as the snow level lowered dramatically.  The 00z version doesn’t show that…it just shuts down the precipitation after 8pm or so.

Our best chance for lower elevation snow will probably be late tomorrow night or early Wednesday morning as the cold upper-level trough slides through.  Models (and satellite) show a vigorous batch of showers passing overhead between midnight and 8am.  I think that guarantees a decent 1-3″ at/above 1,000′, and maybe something all the way down to sea level if the precipitation is heavy enough.  In our favor is no mild southwest wind.  So I’ll say zero to a trace at the lowest elevations, but 1-3″ at/above 1,000′. 

As I’ve mentioned numerous times, the elevation distinctions are approximate, especially with the showery nature of the precipitation coming through.

During the day Wednesday, with sunbreaks and lighter precipitation, temps should rise to around 40 degrees or so.

Thursday morning COULD be interesting, but the mesoscale models keep the moisture to our south as a wave slides down the Coast.   The much lower resolution GFS has precipitation over us, but since we’re at the edge of the precip…we’d be arguing over grid points on that one.  Either way generally dry from Wednesday evening through sometime early next week.  Colder too as higher pressure settles east of the Cascades beginning Thursday.  Not a big blast by any means, but seasonably chilly for late December or early January.

One other weather forecasting issue:  New Year’s Eve and/or New Year’s Day.  GFS has been very insistent in pushing a weak system through the developing ridge overhead.  The system holds together far more on this model than others.  The ECMWF has a full-on split and takes all precipitation to our south.  If the GFS verifies, we would probably have some snow on New Year’s Eve.  At least a trace, maybe 1-2″?  The GFS would also warm things back up to normal quicly either Saturday or Sunday…warmer at least than our 7 Day shows.  I’ve left the forecast dry, hoping for a change on either the 00z ECMWF of 12z GFS.

Chief Meteorologist Mark Nelsen

70 Responses to Monday PM Update

  1. […] the rest here: Monday PM Update « FOX 12 Weather Blog […]

  2. Bob says:

    My forecast as of right now: Light rain changes over to light snow around dinner time as temps start to plummet, moderate snow begins to take over during the overnight hours. As the L jogs to the NE to Idaho, even colder air will arrive. Snow continues into tomorrow tapering off in the afternoon. Since we will be snow covered, highs will not make it out of the 30s, might even see highs around freezing or lower especially if moisture doesn’t run out and there us cloud cover. As for amounts around the PDX area, anywhere from 4 to 8 inches is my best guess. Higher of course as you climb in elevation. I know one thing for sure, when people wake up tomorrow morning, it’s going to be a WINTER WONDERLAND!

    ~Meteorologist Bob

  3. Mark Nelsen says:

    New post this morning

  4. pappoose in scappoose says:

    Quick men, gather the women and children…get them to a safe place…the snow man cometh.

  5. wendy-silverlake,WA says:

    I don’t know how to read them all that well, but looking at the runs for up this direction, we seem to be a bit deprived of moisture. Am I reading this correctly?

    • wendy-silverlake,WA says:

      In terms of the next few days and snow.

    • Ryan (Walnut Grove) says:

      General theory is that moisture is ending as the cold front moves in. As NWS indicated there is some interesting development with the low providing us moisture and timing though.

  6. bgb41 says:

    Did anyone see Steve Pierce’s latest post on the Sandbox thread? Hope it really happens.

    • Bob says:

      Yup I saw it and I absolutely agree with him 100%! This snowstorm is going to surpise a lot of people.

    • Derek Hodges says:

      Not us! lol Not to be prideful or anything but I have vocally been noting the possibility of wraparound moisture turning to snow for days with this. 🙂

  7. HeatherWeather says:

    I am praying for something drastic to happen Wed. and Thurs. my Mom came from Arizona for Christmas and I don’t want her to leave LOL. Come on snow her in!!!!

  8. PaulB/Eugene says:

    South Valley Snow Surprise on the NAM this morning for tomorrow?

    The NAM paints 3-6 inches of snow over the S Valley. I would be pleasantly surprised if it verifies. If it did there would be some power outages due to wet snow loading branches etc.

    Gfs much more stingy but still manages 1/2 inch in Eugene

    • PaulB/Eugene says:

      The NAM actually has 10 inches of snow for areas just SE of Eugene (areas above 500-600 feet).

    • Andrew Johnson says:

      Yes Paul it seems to me that places in the mid and south valley are favored just as much if not more as PDX for this possible event. As it is not a gorge/east wind snow setup and we are closer to the low, hence heavier precip. This kind of setup is usually the kind we do well with i.e. 01/01/04, etc…

    • Snow-Zone/Monmouth-Elv200' says:

      I got 6″ of snow on 1-1-04. On top of the 8″ I got the evening after Christmas in 2003. December 26-27.

    • Andrew Johnson says:

      Ya Snow Zone, the mid valley really scored in that stretch during 03-04. Especially with the first storm. I believe the dates on that one actually were Dec. 28-29.

    • Snow-Zone/Monmouth-Elv200' says:

      Ok Andrew… Your probably right on those dates.. I didn’t keep records. Just went off memory. But that was a lot of fun back then.

    • Andrew Johnson says:

      You actually got more than I did during the 12/28-29/03 storm. The rain transitioned to snow on the westside of the mid-valley first. It took hours and hours for it to finally switch to snow here in Silverton. My brother and I waited up for to finally transition at about 230am. Ended up getting about 4 1/2 inches here. The next day I drove around and noticed the accumulating snow stopped just north of Mt. Angel. I went up on a nearby hill and looked north and even the hills up toward Oregon City were bare. To the south and west though it was nothing but white!

    • Snow-Zone/Monmouth-Elv200' says:

      Yeah the rain transitioned to snow here at about 10:30 that night.. That is one memorable night.. I think the mets said I would only get 4″ of snow.. But the real amount was double that!

  9. alohabb says:

    If the threat of snow is getting better, dont the posted highs for the upcoming days seem to high?

  10. PDX Weather Nut says:

    Snow snow snow … need snow! The cold rain and gray skies have gotten very depressing as of late …

  11. alohabb says:

    Bob, I have not seen this side of you! You seem pretty certain that we will get some good snow, as compared to events in the past. So what day are we talking about getting snow,and how long will it stay around?

  12. Jacob PSE-BPA says:

    Its amazing how models show something within 5 days then they hit reset button then comeback and really nail it within 24-48hrs

    So I will have some thought on what is to occur I dont see 6″ but 1-3″ seems more releastic Im really looking at Friday into Sat as a good one also

  13. Andrew Johnson says:

    Ya don’t get to excited guys, you could get let down. But there is some potential there.

  14. Bob says:

    The 12z NAM and 12z GFS are tremendous as around noon tomorrow we see the L race NE into Idaho which allows frigid arctic air to spill in behind along with plenty of moisture, up to 5 to 6 inches of snow.

    NAM:http://oi56.tinypic.com/acdjig.jpg

    GFS:http://oi51.tinypic.com/w06lfp.jpg

    Both models are in absolute agreement that there will be PLENTY OF MOISTURE once the cold air comes spilling behind the low!

    🙂 =p~

  15. Bob says:

    Wow!

    THE FRONTAL BOUNDARY WILL BE SLOW TO PUSH SOUTH TODAY. IN FACT…THE
    LATEST MODEL RUNS ARE NOW SHOWING A SIGNIFICANT LOW FORMING OFF THE
    SOUTH OREGON COAST THIS EVENING AND MOVING NE ALONG THE FRONT TOWARD
    NE OREGON OVERNIGHT. THIS SOLUTION COULD PRESENT A NUMBER OF
    POSSIBLE PROBLEMS ACROSS THE FORECAST AREA. GUIDANCE SUPPLIES THIS
    DEVELOPING LOW WITH AMPLE MOISTURE AND THIS COULD BRING QUITE A BIT
    OF RAINFALL TO AREA RIVERS…MANY OF WHICH IN THE COAST RANGE WILL
    BE NEAR BANKFULL. ANOTHER CONCERN MAY BE PRECIPITATION TYPE. NAM
    BUFR SOUNDINGS SHOW THE ATMOSPHERE BECOMING ISOTHERMAL ACROSS MUCH
    OF THE INTERIOR AFTER 08Z WEDNESDAY AS THE LOW MOVES NE OVER THE
    CASCADES. THIS SEEMS SOMEWHAT REASONABLE GIVEN THE HEAVY PRECIP THAT
    THE NAM PRODUCES TOGETHER WITH THE VERY SHARP COLD FRONT MOVING IN
    ALOFT JUST BEHIND THIS SYSTEM. THIS SETUP WOULD HAVE THE POTENTIAL
    OF DRIVING THE SNOW LEVEL TO THE SURFACE ACROSS MUCH OF THE
    INTERIOR.

    🙂

    • Jacob PSE-BPA says:

      Now you want to play the snow dance LOL

    • Bob says:

      I’m dancing right now! If every goes right, we could get 6 inches of snow in and around the PDX area.

    • dave says:

      Bob, weren’t there a few more sentences of the AFD after you cut it off? I believe they went something like….

      THIS THREAT OF LOW ELEVATION SNOW FOR LATE TONIGHT BEARS
      WATCHING BUT CONFIDENCE IS LOW.

      ONCE THIS LOW MOVES INTO THE CASCADES TONIGHT THE TRAILING COLD FRONT
      WILL DROP IN FROM THE NW WITH COLD ONSHORE FLOW. THIS COLD
      FRONT WILL BRING MUCH COLDER TEMPERATURES…ALONG WITH BREEZY W TO NW
      WINDS TO THE REGION. THE AIR MASS WILL TURN COLD ENOUGH ON WED TO
      SUPPORT SNOW SHOWERS TO NEAR THE VALLEY FLOOR. HOWEVER…FOR THE
      LOWLANDS…NOT AN IDEAL SET UP AS NW FLOW USUALLY DOES NOT BODE WELL
      FOR STICKING SNOW IN THE LOWLANDS. STILL…WILL SEE MINOR
      ACCUMULATIONS IN MANY AREAS…BUT BEST THREAT OF 1-INCH PLUS WILL BE
      ON THE HIGHER HILLS AND OF COURSE THE MOUNTAINS OF BOTH COAST AND
      CASCADES RANGES.

    • Andrew Johnson says:

      Ya Ben if that verified there would be a chance of snow all the way to at least Eugene.

  16. Andrew Johnson says:

    If the 06z NAM verified it would be a decent snow for pretty much everyone all the way down the valley. 12z doesn’t look quiet as good, but it bears watching as this is a juicy dynamic system. Also it appears quite a temp gradient developing as temps in NW Oregon are approaching 50 degrees, it will be interesting to see how the cold air approaching later on interacts with the warm air as it drives it out.

  17. Bob says:

    Well I’ll be, models now showing better agreement that we will be cold enough starting Tuesday evening for sticking snow all the way down to the valley floor, 6z NAM which was very accurate during the Nov cold snap shows PDX getting over 5 inches of snow here in the city. Moisture will not be an issue, just a matter when the switch over to snow will begin, the earliest the more sticking snow we can get. We can get anywhere from an inch or 2 to as much as over 5 inches. What is now certain is that WE WILL GET AT LEAST 1 or 2 inches because moisture will be here.

    http://68.226.77.253/text/MESOSFC/NAM_Kpdx.txt

    • OSUBeaver says:

      Did you just say it’s certain we will get snow to the valley floor?!?! I’d love it if the NAM were right, but dang…nothing’s ever certain here.

    • Bob says:

      Yeah, temps will be at or below freezing combined with no SW or S wins are every thing that falls will be in the form of sticking snow :). Precip is now being delayed by the models which is a good thing because the cold air will get here sooner before the bulk of the precip arrives.

  18. Bob says:

    Thanks for the update Mark, I think we will be way too warm even if there is enough moisture this Tuesday late night into Wednesday morning, so any sticking snow will be above 1000 feet. As for the system New Years eve, the ECMWF will be right in this one as a split flow will occur and take all the moisture to our south.

    http://www.cascadeaccess.com/~mnelsen/Models/ecmwf500mb_ecmwf.html

  19. Yevpolo1990 says:

    Typical shower crap, I end up being the coldest and get no precip because of the rain shadow, this is like catch a flake game. OVER
    Only possible opportunity is maybe Wed night into Thursday, but then ECMWF took that away too….
    Then GFS does show us being cold enough on Saturday for some very nice moisture as well, but then ECMWF took that away too.
    Wow, this is disastrous….

  20. Karl Bonner says:

    So let me get this straight: the GFS has moisture on New Year’s Eve but it warms up on New Year’s Day or early Sunday? Isn’t it just possible that either we are reading it wrong or the model is a bit off on the timing, and that the weekend disturbance will in fact push the cold air out itself?

    • Karl Bonner says:

      Of course, snow is still possible if it were to turn out this way, but it wouldn’t stay on the ground very long before moderating temps melted it away.

  21. Snow-Zone/Monmouth-Elv200' says:

    The rain has been devastating down here

  22. Andrew Johnson says:

    Really pouring out right now. The radar shows a lot of bright colors.

  23. PaulB/Eugene says:

    Looks like it will be difficult to get any accumulation of snow on the valley floor, especially toward Portland, as most of the shower activity will be during the middle of the day on Wednesday…expect temps in low 40s during that time with intense showers bringing temps down only into the upper 30s for maybe a mix down low.

    Farther S, if showers linger into the late evening/night..there could be some accumulations if you gain any elevation above the valley floor. I think S Salem hills might get an inch and likewise the hills around Eugene will probably get an inch. If shower activity is intense, it might even snow at Eugene airport in the evening Wednesday but it won’t stick. All in all not too impressed with this…just a midwinter transitory maritime polar cold snap with snow in Sandy, etc.

    Looking at long range models/ensembles…am less optimistic about an arctic blast in second week of January than I was a couple days ago. Looking at the 6-10 and 8-14 day CPC 500mb analogs….still seeing that big positive anomaly around Greenland/Davis Strait…

    • Jesse-Orchards says:

      I don’t know why you would be less optimistic about an arctic blast the second week of January. Have you seen the 00Z GFS ensembles? They are great. The ensembles keep getting better and better.

    • PaulB/Eugene says:

      Must admit tonight’s GFS ensemble runs for long range show some possibility of colder weather…but we still we have to put up with a 5-7 day stretch of rather mild temps beforehand

  24. Mark Nelsen says:

    00z ECMWF is staying dry with a good split still. No precipitation through at least Sunday (after Wednesday).

  25. Rob "Wrath" S.E. Portland says:

    00Z GFS Ensemble support continues to consistently be very good. If there is one thing we can be somewhat optimistic about it is this. The operational runs should improve in the coming days.

    00Z EURO in 28 minutes!!!!!!!!!

  26. Derek Hodges says:

    Very good post Mark, mirrors my thoughts exactly. Probably everybody sees snow fall. Snow in the heights of the city, and possible but uncertain in the valleys. Also Friday afternoon is looking good.

  27. jackfrost (beaverton) says:

    I’m gonna go out on a limb and say that any rain that falls tonight will stick! Expect to wake up to wet concrete people! This is it, this is the big rain we’ve been waiting for!

  28. Jethro says:

    Yep. That sounds about right…

  29. Ben Randall says:

    I like how Euro shows -6 degrees right over Tillamook or close Wednesday morning ,

  30. Ben Randall says:

    I agree mark I think the coast would have the best chance of snow just because that coast range messes you guys up all the time

  31. wendy-silverlake,WA says:

    I do really good with moisture coming from the NW. No big hills that eat the rain/snow/what not up. Hopefully get a few flakes in the air the next week.

  32. Are we still able to cat fight because I’m about ready to go postal on Mark.

  33. Rob "Wrath" S.E. Portland says:

    Mark, thanks for the detailed update. Probably in your top 15-20 of all-time.
    _________________________________________
    00Z after Wednesday night/Thursday is a downer. Long range is crummy at best. That could easily change since we’re talking about beyond 7-10 days. In fact I would expect it to do so. I will say that I’m beginning to lose a bit of optimism for a “big” Winter or at least a significant Arctic Blast or significant Snow Storm.

    • bgb41 says:

      00Z @ Troutdale

    • Rob "Wrath" S.E. Portland says:

      I hadn’t looked at finer details. As Tyler pointed out the 00Z WRF sounding is showing snow 10 PM Friday.
      http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d2_x_snd_kpdx+///3
      Notice how the atmospheric in the mid-upper levels begins to dry out around 7 AM Thursday and then the drying/cooling aloft is more prevalent after 4-7 PM Thursday setting up the evaporative cooling shown at frame 35. Light easterly surface winds mmmm well a bit promising.

    • Ryan (Walnut Grove) says:

      Nothing showing through mid-January gives me little faith anything happens.

      I will, however, hold on hope that something will come around by mid-February. If nothing shows up by then I’ll surrender on any fun for this winter.

  34. pappoose in scappoose says:

    I’ll take a 20% chance and run with it any day.

  35. bgb41 says:

    Not looking to good on the 00Z

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