Tuesday Midday Update

11am…

I’m pretty happy with how that tricky forecast worked out; everyone saw snow but not everyone had sticking.  Plenty up in the hills, I had about 3″ here at 1,000′ east of Corbett.  Put your snow totals (if you had more than 1/2″) in the posting below.

The Highlights:

  • Snow showers continue today mixed with sunbreaks, much like yesterday although a little colder.
  • We dry out around the evening commute and through midnight.  No travel issues for the evening commute.
  • A snow/rain mix for the lowest elevations resumes around midnight, then all rain after 3am
  • Near/above 1,000′, it’ll be all snow around midnight for 3-4 hours.  Could see 1-2″ up there.  Then all rain after 3-4am even on the hills
  • Tomorrow morning’s commute will just be wet

Showers taper off this afternoon as the coldest air and instability moves off to the east, then we have a dry and chilly evening.  By the way, the morning sunday at Salem was a -6.5…just about as models anticipated.

A very wet frontal system moves inland later tonight and tomorrow morning.  Precipitation appears to arrive right around midnight and with the cold airmass overhead there is a very good chance it starts as a rain/snow mix even to the lowest elevations.  The sounding looks very similar to Saturday morning’s event; so I expect sticking snow again closer to 1,000′, but very unlikely it’ll stick much lower.  I think this is pretty much a rain event for most of us.  For those of you in the hills, the action will be from Midnight to 4am.  Could see 1-2″ up around and above 1,000′.  It’ll end quickly at that time though as much warmer air floods in from the south and southwest.

The 12z WRF-GFS 3 hours snow total from 1-4am captures it just about right:

or_snow3_24_0000

Lots of rain tomorrow, a very wet Wednesday ahead.

Chief Meteorologist Mark Nelsen

211 Responses to Tuesday Midday Update

  1. KPTV Tower Temps
    As of 8 PM(1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 29.5
    Middle Sensor(1473′) 30.0
    Lower Sensor(1043′) 31.1
    Tower Temps all cooled

    05z(9 PM) Upper Air Analysis(Observed over PDX)
    925mb: -2.2c
    850mb: -7.4c
    700mb: -17.1c
    500mb: -27.8c

  2. ChrisR says:

    Although I have low expectations for the night, it’s good to see the tower temps falling once again.

  3. PDX NWS AFD is out
    AREA FORECAST DISCUSSION
    NATIONAL WEATHER SERVICE PORTLAND OR
    836 PM PST TUE DEC 18 2012

    SATELLITE IMAGERY SHOWS AN APPROACHING WARM FRONT AROUND 150 MILES OFF THE OREGON COAST. THE LANGLEY HILL RADAR IMAGERY IS JUST SHOWING RAIN OR VIRGA AHEAD OF THE FRONT AROUND 70 MILES OFFSHORE OF THE WASHINGTON OREGON BORDER. WARMER AIR WILL EVENTUALLY MOVE INTO THE AREA AND RISE SNOW LEVELS…BUT NOT LIKELY WITH THE INITIAL BAND OF PRECIPITATION.

    EASTERLY WINDS EAST OF THE CASCADES WILL PUSH MUCH COLDER AIR FROM EASTERN OREGON THROUGH THE GORGE BEFORE THE ARRIVAL OF PRECIPITATION…AND CAN EXPECT A GOOD DOSE OF SNOW FOR THE GORGE AND UPPER HOOD RIVER VALLEY LATE TONIGHT INTO WEDNESDAY MORNING. SOME OF THIS COLDER AIR WILL SPILL INTO THE NORTHERN WILLAMETTE VALLEY AND SUPPORT THE POSSIBILITY FOR SNOW IN THE INTERIOR LOW LANDS AS WELL.

    THERE IS FAIR CONFIDENCE THAT SNOW WILL IMPACT MUCH OF THE AREA BEFORE THE WARM FRONT BRINGS WARMER AIR BUT THERE IS LESS CONFIDENCE IN THE AMOUNT OF SNOW.PRECIPITATION LOOKS FAIRLY LIGHT WITH THE INITIAL SLUG OF MOISTURE WHICH SHOULD LIMIT ACCUMULATING SNOW. HAVE MAINTAINED THE CURRENT FORECAST OF HAVING LIGHT SNOW DEVELOPING AFTER 3 AM…BUT NOT REALLY ACCUMULATING UNTIL AFTER 5 AM. THE INTERIOR LOWLANDS SHOULD HAVE ALL SNOW EARLY WED AM…TRANSITIONING TO SLEET AND THEN RAIN AND SNOW BETWEEN 7 AM AND 9 AM…THEN JUST RAIN. 1 TO 2 INCHES GENERALLY EXPECTED WITH A FEW AREAS GETTING UP TO 3 INCHES. BUT IN CENTRAL AND SOUTH WILLAMETTE VALLEY…ESPECIALLY FROM SALEM SOUTHWARD…THE WARM AIR ARRIVAL SHOULD LIMIT SNOW AMOUNTS TO LESS THAN 1 INCH.

  4. For those thinking of offshore flow, I don’t see any yet, and all of the models show very little if any offshore flow.

    • 00z WRF 4km implies offshore flow tries to develop 4-5mb, but there is no area of high pressure east side. Looking in the Columbia Basin:
      Moses Lake and Ephrata are around 20, Pasco 34, but The Dalles at 31.. just wouldn’t be a great deal of help IMO…. If we saw a light gradient if anything the only thing I could see it doing would be to slightly hold back the low-level southerly push in immediate PDX metro(especially east of I-205)….. I just feel we will not develop strong enough east wind and not have the duration needed to pull in cold/dry enough air to matter.. I really see NO chance of that.

    • Plus if we even get 33-35 degree air pushing in up above, it could be 32 here which wouldn’t be cold enough for snow or freezing rain. I hate even mentioning freezing rain. But, I have seen it rain and not freeze at 32 degrees. For freezing rain to work you really need the water to be “super cooled”

    • W7ENK says:

      While living down in Klamath Falls, I sat at the college and watched it pour rain at 28 degrees for 5 hours, no snow, no ice. I have no idea how that’s even possible, but this is truth.

    • Chris says:

      Rob…I don’t expect significant help from East winds either. Just a note about East winds. They don’t blow they suck. You don’t need a high on the east side you…you can accomplish the same thing by lowering pressure on the west side. Thanks for all your insight on the blog.

    • It’s helpful to have a closed upper level high east side though.. and yeah, we just have a pressure change that would cause an easterly gradient.

  5. paulbeugene says:

    Seems cold enough for most areas to have brief period of snow before transition to rain down low.
    NAM mm5 12km run Monday morning was accurate for snow in south valley last night and this morning….GFS showed no snow.

    mesoscale models not showing low snow for tonight in western Oregon, other than near gorge.
    Washington should have a bit more accumulations before transition, particularly around Hood Canal.

    Long range continues to show tendency for low 500mb heights over western USA but no major league arctic air to be found. The snow from the past 24 hours was a reminder that arctic air is not a prerequisite for snow in the Willamette Valley. With continental cold air pool in the interior, have to watch for lows approaching from the SW.

    Long range ECMWF suggests cold start to January
    http://www.accuweather.com/en/weather-blogs/anderson/long-range-model-outlook-trending-colder-in-the-east/2875704

    • I’ve harped many times on the idea that we don’t get all our snow from the over-running events. I grew up in P town and Corvallis and I can tell you that many, many times we got more accumulation in Corvy than Portland during the big cold events. However, Portland does get snow more often due to the “transition event”. But who cares cuz it’s just gonna melt in a few hours anyway. My favorite storm is when the flow is coming down from the north, it’s been raining for hours when suddenly it turns to snow. It snows all day. Then the big H moves in and we have snow on the ground for several days along with sunshine!
      But I will say that as a kid, those ice storms in our neighborhood in SE Portland were serious fun!

  6. alohabb says:

    Those top 2 tower temps are on the rise so get the kids to bed, school is on.

  7. KPTV Tower Temps
    As of 7 PM(1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 30.0
    Middle Sensor(1473′) 30.6
    Lower Sensor(1043′) 31.5

    04z(8 PM) Upper Air Analysis(Observed over PDX)
    925mb: -2.5c
    850mb: -7.4c
    700mb: -17.3c
    500mb: -27.8c

  8. AlohaWeather says:

    34.9F
    If steady snow starts after midnight, won’t it cool down the atmosphere by a few degrees? That would help the snow stick, wouldn’t it?

  9. Wendy-Silverlake, Wa says:

    It’s currently 30 degrees here and the roads are an absolute sheet of ice. Hope it snows soon to cover that up.

  10. SNOW! says:

    Rod hill has the best hopes for snow. He says its a possibility that the east wind will hold portland’s temperature down to 30-32, and the moisture will be all snow, or a snow/sleet mix, and city center portland could get 1-4 inches, and elevations 300 feet or higher could see 3-4 inches by sunrise and another couple inches in the morning before all the snow turns to rain by 11:00 AM. Here is a link to his weather blog. WATCH THE VIDEO!!
    http://www.portlandweather.com/portland-salem-weather.html

  11. IF…and I do mean IF my temp continues to drop at the rate it has the last two hours, it will be 34 at 8 AM hahahaha

    It has dropped from 36.1 to 35.8 since 6 PM.

  12. 00z MM5-NAM Analysis
    First, let’s look at the setup for tonight-tomorrow morning.
    Tonight-Wednesday AM
    http://www.atmos.washington.edu/~ovens/wxloop.cgi?mm5d2_e_slp
    925mb temps forecast to hover around 0c until 7:00 AM. No offshore flow/east wind shown just a moderately light southerly flow.

    12km Sounding(PDX)
    http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d2_e_snd_kpdx
    925mb/SLP/Surface Wind Model
    Surface temps never drops below +3c. Maybe a mix around Midnight, but it isn’t looking promising below 500-1000′ Temperatures aloft and down at the surface warm quickly after 7 AM. No Snow. WRF will be out soon, so I’ll look at that too….

    Onto something mildly more interesting….
    7:00 AM Friday
    http://www.atmos.washington.edu/mm5rt/data/2012121900.naminit/images_d2/slp.63.0000.gif
    I like that small, yet very compact 996mb well southwest of the Oregon Coast that races northeast with an excellent trajectory and track. If that was even just 987-990mb it could produce a quick hitting 2-3 hour wind storm.
    Wind Gust Model verifies this
    http://www.atmos.washington.edu/mm5rt/data/2012121900.naminit/images_d2/wgsfc.66.0000.gif
    Tiny core of 40-50kt gusts for the northern Willamette Valley.

    Cross Section model(PDX)
    Also implies gusty winds with 50kts down to 975mb.
    Salem Even more impressive 975mb near the surface

    IF BUT MAYBE WHEN MIGHT COULD SHOULD WOULD. Suppose it’s something to keep an eye on(or both eyes if you have that kind of time.)

  13. LurkinginFG says:

    Check out some of the mesonet station temps at the coast. Rather cool. 35 in Tillamook and Astoria.

  14. KPTV Tower Temps
    As of 6 PM(1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 29.8
    Middle Sensor(1473′) 30.2
    Lower Sensor(1043′) 31.3

    03z(7 PM) Upper Air Analysis(Observed over PDX)
    925mb: -2.8c
    850mb: -7.5c
    700mb: -18.0c
    500mb: -38.0c

  15. chris says:

    31 here in Puyallup snow on everything but the roads still, but the slush from melting is now ice.

  16. Ryan says:

    Just drive down hwy 26 and noticed the big flag at shilo inn is blowing towards the northwest(SE wind). Not quite east wind but better than straight south!

  17. I just poured over a lot of data, observations, upper air info, and pressure gradient analysis and based on all of those things I have come to this conclusion. My final thoughts are if you look out the window and don’t see anything, then there probably isn’t anything going on. If you look under the street light and see white things, that is likely snow. If you don’t and it looks wetter, I am guessing it would be rain. If you look at the ground and it’s bare, that probably means nothing, but if it’s white I am assuming that is because snow was falling.

  18. vernonia1 says:

    NWS says snow Friday. Wonder if Mark concurs??

  19. Jordan (Raleigh Hills, 420') says:

    Down to 35 in Raleigh Hills. About the same as last night, but curious to see if radiation cooling will play a role tonight. looks like it might be clear to partly cloudy for awhile.

  20. pappoose in scappoose says:

    Let’s see if the east winds can crank up in the gorge this eve.
    Biggest player in big snow for us. Vista House

    http://www.wrh.noaa.gov/mesowest/getobext.php?wfo=pqr&sid=D6193&num=60&raw=0&banner=off

  21. KPTV Tower Temps
    As of 5 PM(1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 29.8
    Middle Sensor(1473′) 30.6
    Lower Sensor(1043′) 31.6
    *All Tower temps are now below freezing.

    02z(6 PM) Upper Air Analysis(Observed over PDX)
    925mb: -2.5c
    850mb: -7.3c
    700mb: -17.8c
    500mb: -30.0c
    *Slight cooling aloft 925-850mb(2500′ – 5000′)

  22. LurkinginFG says:

    33.1….. anyone else notice how wunderground forecasts have been rather off lately? They used to be fairly reliable with the precipitation type and amounts, but wow. They have put my forecasted area with snow all week except one day and calling for an inch every snowy day. I will say that their precip map has been on the mark for precip type(in the moment). Again, pardon the grammar… using a darn Android phone to post. It’s not easy to proof-read as you type.

    • Brandan (Damascus - 675ft) says:

      This confused me at first as well and wondered if NWS had changed their forecasts. Towards the top of the page right below your city or town name, lye’s an option to change from “Best Forecast” to “NWS.” Wunderground automatically used “Best Forecast’s” forecast. I’m assuming it has something to do with money..

  23. kcteach Gresham 500' says:

    34.7 here. Someone said it earlier, but it just feels colder out there. No real wind to speak of.

  24. alohabb says:

    34 and mostly clear. Any cooler and these wet streets gonna be icy!

    • pappoose in scappoose says:

      Haven’t noticed it brought up lately.
      If you move the cursor onto the temp line, you can get the temp/time.
      What did I just say? Hahaah!

  25. *BoringOregon* says:

    HEY MARK check this link out its on the “cops” facebook page–https://www.facebook.com/copstv?ref=stream

  26. alohabb says:

    34 now in Aloha

  27. Marc (East Vancouver) says:

    The best forecasters out there will base their prediction not solely on the models, but on their experience in the field and the general area. Not many will step out on a limb and do that. Mark seems to do a good job of finding that balance and tonight is no exception. However, most local meteorologists are saying this is a non-event anyways.

    • Marc (East Vancouver) says:

      What I’m trying to say is that I have much more respect for a humble forecaster, amateur or not, who doesn’t blame the models for a blown forecast.

    • Ben T says:

      I agree, why do we continuously blame those pretty blondes! It doesn’t seem fair to them!

  28. Lightly snowing, deg. 33.3, wind 3 (I wish I could say the direction was 333 deg. unfortunately it’s more like 180)

  29. Andrew (Beaverton...Murray Bldv....250 feet) says:

    Already down to 34 here, impressive drop the last 2 1/2 hours.

  30. KPTV Tower Temps
    As of 4 PM(1 hour lag. Updates every :15 after the hour)
    Upper Sensor(1818′) 30.6 | 3 PM: 30.6 | Hourly Change: -0.2F
    Middle Sensor(1473′) 31.1 | 3 PM: 31.1 | Hourly Change: None
    Lower Sensor(1043′) 32.2 | 3 PM: 32.2 | Hourly Change: None

    01z(5 PM) Upper Air Analysis(Observed over PDX)
    925mb: -2.0c | 4 PM: -2.0c | Hourly Change: None
    850mb: -7.0c | 4 PM: -7.0c | Hourly Change: None
    700mb: -17.6c | 4 PM: -17.5c | Hourly Change: +0.1F
    500mb: -35.0c | 4 PM: -35.0c | Hourly Change: None

    PDX-DLS: +1.2mb | 4 PM: +1.3mb | Hourly Change: 0.1mb Decrease
    PDX-EUG: -1.8mb | 4 PM: -2.1mb | Hourly Change: 0.3mb Decrease
    OLM-PDX: -2.1mb | 4 PM: -2.0mb | Hourly Change: 0.1mb Decrease

  31. Rusty (165th Beaverton 259') says:

    34 now with a rain/snow mix. Hope the cold air sticks around for more than the sloppy dusting I had on my car this morning.

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