Exciting (and Snowy!) Saturday Morning Ahead

I just checked the latest maps & models, and tomorrow morning screams “SNOW IN THE AIR” here in the metro area.

For those just wanting the basics, here you go:

MarkSnow_Outlook_Extended

  • As precipitation arrives between 7-10am, there is a very good chance it’ll be a rain/snow mix or even all snow IN THE AIR to the lowest elevations from about Wilsonville north to Longview.
  • Brief sticking (maybe turning white) is possible anywhere above 500′ and even below that elevation on the far westside of the metro area (Forest Grove, Banks, Vernonia etc…)
  • This means the West Hills, Bald Peak, Mt. Scott, Sandy, and northern Clark County will see the first snow of the season.
  • It won’t last long (1-2 hours) as a warming south wind arrives soon after midday.
  • If you live near/above 1,500′, you could see a quick 2″!

9:30pm Update:

We have 2 two chances for snow in the lower elevations over the next 7 days with a strong wind event sandwiched in between. 

FIRST SNOW TOMORROW MORNING

A  bit more on why I’m so bullish on at least seeing snow in the air tomorrow:

1. This morning we saw a lower snow level than expected with sticking snow briefly in spots down around 1,000′ or even lower.  I had my first trace of the season and the trees just above my house at 1200′ were all white.   All model data points to a slightly colder atmosphere tomorrow morning and heavier precipitation.

2. Cold night tonight with temps down around freezing and/or well below 40 degrees.  We’re set for a 7-9am precip arrival time, the timing doesn’t get any better than that.

3. Calm wind doesn’t bring in any warmer air from any direction until after 10am.  Both our model and WRF-GFS show basically calm wind through the metro area north of Wilsonville all morning.  THEN the south wind kicks in.

4. Steady precipitation and drier air up around 1,000-3,000′ should allow some evaporational cooling.  Mesoscale model soundings show this occurring soon after the precip gets going.

5.  Models actually generate sticking snow near the Coast Range.  On the higher resolution WRF-GFS it’s obvious it wants to stick snow down to around 1,000′, notice Bald Peak and West Hills stick out.  Also, the 12z 1.3km version showed other high spots getting a dusting.

rpm4kmsnow

STRONG WIND:

Now let’s move on to the stronger storm later Sunday and early Monday.  All models in agreement now bringing a major storm into the northern part of the Pacific Northwest.  The surface low (down around 970-980 mb) moves into either Vancouver Island or extreme NW Washington.  The orientation of the isobars (east-west across the region) is always good for a strong southerly wind up the Valley.  This low is actually weakening a bit as it moves onshore.  That plus the fact that models don’t want to get too crazy with the valley wind tells me we’ll see gusts maybe in the 40-50 mph range in the metro area.  Most likely the peak will be late Sunday evening through daybreak Monday.  Note a big windstorm, but it’ll match the strongest wind we’ve seen so far this season.

SECOND CHANCE FOR LOWER SNOW MONDAY NIGHT & TUESDAY

This is a totally different low elevation snow setup compared to what’s coming tomorrow.  This time it’s the usual cold and showery airmass coming in off the Pacific behind the early Monday storm.  This pattern is notorious for getting our hopes up for sticking snow to the lowest elevations.  Then we find out in the end it was a little too warm due to a southwest wind bringing in too much mild air off the ocean.  That “onshore flow’ is often a snow killer for the lowest elevations and it may be this time around too.  On the positive side, in the past 24 hours models have shown a slightly cooler solution with 500mb thicknesses down around 520 (very good) and 850mb temps down around -7 deg C.  This is definitely in the “snow possible” category for the lowest elevations.  If so, then it comes down to how much moisture is available.  I think it’s a little too soon to tell.  So I’ll punt on this one for now.

Beyond next Tuesday, all models show warming with a trough digging much farther offshore or some sort of annoying splitty flow as we head towards Christmas.  Notice the 12z ECMWF 850mb ensemble temps all move upward closer to normal after bottoming out Tuesday.  This general progression has been shown on this chart for almost a week:

tseries_850t_000-360_Portland

Chief Meteorologist Mark Nelsen

212 Responses to Exciting (and Snowy!) Saturday Morning Ahead

  1. flurball says:

    OK I’ve got one hand………….

  2. Tyler Mode in Battle Ground says:

    Ill restate: I haven’t seen that gradient packing in any storm in the last several years. Especially with that great orientation.

  3. Tyler Mode in Battle Ground says:

    MEANWHILE…THERE IS STILL THE QUESTION OF WHETHER OR NOT HIGH WINDS
    WILL SURFACE ACROSS THE WILLAMETTE VALLEY AND POINTS NORTH IN
    WASHINGTON. THE LATEST GFS ADVERTISES A 9MB PRESSURE GRADIENT BETWEEN
    KEUG AND KPDX WITH KAST HOVERING NEAR 985MB AT ITS LOWEST PRESSURE.
    THIS IS CAUSE FOR CONCERN. HOWEVER…DUE TO THE EASTWARD MOVING AND
    SLIGHTLY WEAKENING NATURE OF THE LOW PRESSURE AS IT MOVES
    ASHORE…PRESSURE COUPLETS ARE NOT TERRIBLY IMPRESSIVE. WE WOULD LIKE
    TO SEE SIGNIFICANT PRESSURE RISES MOVING IN FROM THE SOUTH AS THE
    SYSTEM MOVES ASHORE…AND THIS JUST IS NOT APPARENT IN THE MODELS.
    THE MODELS PICK UP ON THIS BY KEEPING 925MB AND 850MB WINDS MORE WEST
    THAN SOUTH ACROSS THE INTERIOR…WHICH DESPITE CRANKING AT
    40-60KT…WILL NOT BE TERRIBLY FAVORABLE FOR SOUTH WINDS TO CHARGE UP
    THE VALLEY. NONETHELESS…SUSPECT THE A WIND ADVISORY WILL STILL BE
    NECESSARY…AND WOULD STILL NOT BE SURPRISED IF WE NEED TO PUT OUT
    HIGH WIND WARNING FOR THE INTERIOR. THE BOTTOM LINE IS THAT THERE
    WILL LIKELY BE AT LEAST ISOLATED TO SCATTERED POWER OUTAGES DUE TO AT
    LEAST A FEW FALLING TREES WITH THE CURRENT SATURATED SOIL.

    • W7ENK says:

      HOWEVER…DUE TO THE EASTWARD MOVING AND
      SLIGHTLY WEAKENING NATURE OF THE LOW PRESSURE AS IT MOVES ASHORE…PRESSURE COUPLETS ARE NOT TERRIBLY IMPRESSIVE. WE WOULD LIKE TO SEE SIGNIFICANT PRESSURE RISES MOVING IN FROM THE SOUTH AS THE SYSTEM MOVES ASHORE…AND THIS JUST IS NOT APPARENT IN THE MODELS.

      Not too encouraging if you like exciting weather…

      And by the sounds of this, NWS “would like to see” damaging winds? Isn’t that a bit morbid for a government agency???

    • Sandi (Wilsonville) says:

      I see how one could read it that they are hoping to see damaging winds, but I took it to mean they are looking to see a better scenario before issuing warnings.

  4. 00z GFS was better. Check out the 500mb pattern evolution
    http://mag.ncep.noaa.gov/NCOMAGWEB/appcontroller?prevPage=Model&MainPage=index&image=&page=Param&cycle=12%2F16%2F2012+00UTC&rname=UPPER+AIR+PARMS&pname=500_vort_ht&pdesc=&model=GFS&area=NPAC&cat=MODEL+GUIDANCE&fcast=Loop+All&areaDesc=North+Pacific+-+Western+US+Alaska+Western+Canada+Hawaii+North+Pacific+Ocean&prevArea=NPAC&currKey=region&returnToModel=&imageSize=M
    I like how the ridge axis is closer to 160 W then slightly east with the trough digging offshore closer to us, then a lobe off the PV pushes south through BC seeming to re-energize the trough supplying cold, modified arctic air into eastern Washington. To me it looks like a step in the right direction if you want improved cold/snow chances for PDX. It’s also fairly close to being quite cold for an extended period.

  5. Things to do in Punta Cana says:

    I read this paragraph completely regarding the resemblance of newest and previous technologies, it’s awesome article.

  6. 8:42 PM Update

    Windstorm potential increasing for PDX now

    00z WRF now has the low a bit deeper roughly 972mb moving into southern tip of Vancouver Island.
    4:00 AM Monday
    http://www.atmos.washington.edu/mm5rt/data/2012121600/images_d2/slp.36.0000.gif
    A very tight gradient sweeps inland with a max PDX-EUG of -7 to -9mb. Isobars are aligned perfectly perpendicular in a E-W orientation stacked ideally over the Willamette Valley to allow for maximum efficiency. Also, the bent-back occlusion may swing inland into NW Oregon enhancing the winds further.

    I would expect at the least numerous 40-50mph gusts from Salem to Kelso if not stronger. Wind Advisory or High Wind Watch should be issued soon.

  7. W7ENK says:

    Lots of clearing now, streets are soaking wet. Temperature holding steady, for now. What’s the temp like up above? Southerlies are dying off, it could be an icy mess here in a few hours… :eek:

  8. vernonia1 says:

    when i got off work @ 5…all the snow remaining on the windshield had turned to solid ice! Glad I carry the ice scraper all year long LOL

  9. W7ENK says:

    Snow splats in the rain all the way down I-5 until just North of Salem this afternoon, then the splats disappeared and was just rain only South of about Kaiser. Rain only all the way out 22 past Aumsville/Stayton/Mehama, then rain only up through Silverton/Mt. Angel. Southerly winds were picking up pretty strong, I’d say G20+ on the exposed stands of trees and right along the tops of the rolling hills. Rain only all the way up through Molalla/Mulino, lost the gusty Southerly winds and the splats returned right at the South end of OC (Leland Rd.)

    Southerly winds just starting to pick up (lightly) here at home now, and the temperature is slowly on the rise.

  10. pappoose in scappoose says:

    The Seattle discussion is interesting as well.

    National Weather Service Seattle Washington
    330 PM PST Sat Dec 15 2012

    All eyes are on the next much stronger storm system expected to
    affect western Washington from Sunday afternoon through Monday
    night. The latest forecast models continue to point toward a deep
    975-980 mb surface low developing offshore late Sunday and moving eastward across western Washington Monday morning. There remains some slight timing discrepancies…mainly with the NAM-12 model consistently more progressive and about 3-4 hours quicker than all the other models. If the system moves inland this quickly then some issues such as coastal flooding may be less than the other models imply. The other forecast challenge is the track which will be crucial to which areas get the strongest winds. There was a definite shift among about half of the models toward a bit further S landfall…coming in somewhere from Ocean Shores to the central coast near Cape Elizabeth. This track would greatly diminish the high wind threat across northern parts of western Washington. The worse case scenario is a track like the NAM-12/GFS down the Strait at a slower pace and with falling central pressure as it reaches the area rather than filling. This would likely
    produce a period of strong winds across the entire area…especially
    as the bent back lifts through Monday morning. Decided to issue a
    high wind watch for all the western Washington lowlands due to this possibility. Wind in the mountains is already covered in the Winter Storm Watch statement. Of greatest concern is the S/central Washington coast including the Ocean Shores/Westport areas since wind gusts to 70 miles per hour could be coupled with seas near 30 feet. A coastal Flood Watch was issued to address this. A Post low surge of wind down the Strait could also bring several hours of high wind to the Strait and reaching west facing beaches or land areas near the East Entrance. Wind speeds across the rest of western Washington are more uncertain but if the low takes the northern most track then all areas could experience high winds…40+ miles per hour sustained with gusts 58 miles per hour or higher.

    • You beat me to it. Yeah, interesting they suggest a farther south track now possible….

    • pappoose in scappoose says:

      Will be big time wild here for sure, if the south track comes to pass. Hahaah!

    • marcus says:

      If the low goes farther south would that pull out cold air from the gorge, or does the low need to be way more south say California/Oregon border?

    • marcus says:

      it looks like it is going more south to me by looking at the water vapor imagery.

    • Hope it goes right down the Strait.Not sure what kind of winds we get up here north king county. But with a low that size it surely have to be some strong winds.

    • Marcus even if the low comes directly overhead, it can generate east wind through the Gorge as it approaches. Best if the center tracks just south of the Metro though…

      If the center were way down in southern Oregon THEY’D get a big rain/snow storm and we’d maybe get a few stray showers from time to time, but mostly dry.

  11. Kerry says:

    It has been snowing off/on since 8:00am. Had 2 inches for awhile. Still snowing. Chehalem mt

  12. Don Troutdale says:

    Cascade Locks has snow right now!

  13. lurkyloo says:

    Really coming down here in NE — just rain, have yet to see a snowflake today. :(

  14. Lookie there! I’ll just post the goodies…

    AREA FORECAST DISCUSSION
    NATIONAL WEATHER SERVICE PORTLAND OR
    300 PM PST SAT DEC 15 2012

    OUR FOCUS WILL THEN TURN TO A SHORTWAVE TROUGH CURRENTLY SOUTH OF THE ALEUTIAN ISLANDS. THIS SYSTEM WILL UNDERGO CYCLOGENESIS LATE TONIGHT INTO SUNDAY MORNING AS IT APPROACHES THE OLYMPIC PENINSULA. MODELS GENERALLY AGREE IT WILL MAKE LANDFALL SOMEWHERE IN THE 975-980MB RANGE BETWEEN 06-12Z MONDAY. SOUTHWEST WINDS BEHIND WARM FRONTAL PASSAGE WILL BRING HIGH WIND CRITERIA GUSTS…UP TO 65 MPH FOR COASTAL COMMUNITIES AND UPWARDS OF 75 MPH FOR THE BEACHES AND HEADLANDS…SUNDAY AFTERNOON. WINDS SHOULD SUBSIDE A BIT…BUT REMAIN QUITE WINDY SUNDAY EVENING.

    HOWEVER…GIVEN THE PROXIMITY OF THE LOW PRESSURE TO OUR NORTH…MODELS DEPICT A SECOND DOSE OF HIGH WINDS WILL SLAM INTO FAR NORTHWESTERN OREGON AND SOUTHWESTERN WASHINGTON BEHIND THE BENT BACK OCCLUSION ON SUNDAY NIGHT. THESE HIGH WINDS WILL HAVE THE POTENTIAL TO EXPAND INLAND…PARTICULARLY ACROSS WASHINGTON.

    MEANWHILE…**AT LEAST ADVISORY LEVEL WINDS ARE LOOKING MORE AND MORE LIKELY FOR THE WILLAMETTE VALLEY.** WHILE THE TIGHTEST GRADIENTS LOOK LIKE THEY WILL BE OVER WESTERN WASHINGTON…MODELS STILL DEPICT SOMEWHERE ON THE ORDER OF A 5 TO 8 MB SLP DIFFERENCE BETWEEN KEUG AND KPDX. AS A RESULT… –>A HIGH WIND WATCH MAY BE WARRANTED<–…BUT WILL OPT TO SEE THE 00Z SOLUTIONS LATER THIS EVENING BEFORE MAKING ANY DECISIONS. ULTIMATELY…WE WILL LIKELY SEE ENOUGH WIND THAT AT LEAST A FEW DOWNED TREES ACROSS THE AREA SEEM LIKELY GIVEN THE SATURATED GROUND.

    The plot thickens as they say….

    • pappoose in scappoose says:

      We’re just about into GOLU model time on this. Better get the watch out in time to update it to a warning! Hahaah!

    • runrain says:

      I love the part about the dose of high winds slamming into Northwest Oregon. So ominous sounding!

    • Kyle says:

      This is a special weather reply for you Atmospheric Rob (Wrath) since snow is my favorite topic and you’re the only one that’s been the kindest to me besides Andrew who migrated and I don’t blame him one bit and I have a brand spanking new weather station to play with. :)

      Here is the snow scope (No Scope) Get it?………….Never mind.
      Dad went to Home Depot this morning and right around Centerall Howell the splat test proved positive with a few frozen raindrops. Then Home Depot had a few frozen chunks too.

      We went to Silver Falls Park viewpoint at the very last minute to see if any stuck at 1,000 foot and it looks like there might have been a thin film during the morning showers.

      After looking at weather diaries from England I am making my own persona daily diary starting this morning which I wrote the temps/conditions and remarks about the chance of snow in the air which I need to update since it never happened.

    • Kyle says:

      Edit. I mean Central Howell. *Beep* I was so excited I spelled it wrong and screwed myself.

  15. vernonia1 says:

    hmmm wonder why i can’t copy & paste trip check pics here?????? Still snowing hard. Will the moisture stick around??

  16. vernonia1 says:

    wow really snowing hard now. brought temp down to 34

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