Cold Blast 4 Days Away…

A very cold looking map isn’t it?  00Z models have not backed off at all on the cold airmass coming down from Canada over the weekend and early next week.  The initial surge is a “normal” chilly airmass.  That comes in Friday night and Saturday morning.  Some of the models indicate a little bit of cloud cover and even mountain flurries, but that’s it.  No model shows any sort of significant onshore flow or cloud cover to generate snowfall over us the next 3 days.  By Saturday night a much colder upper-level trough comes down over us from the north.  The map here is for 4pm Sunday afternoon, click on it for a better view.  The upper trough is moving off to our south and at the surface modified arctic air will be pouring in behind it from the north.  So Sunday is the day the really cold air arrives.  I’m assuming models are slightly too cold, so we’ve stayed with high temps Sunday-Tuesday above freezing.  Read literally, the GFS would produce high temps those days closer to 30 degrees (on one side or another), but once again I’m assuming it’s a bit overdone.  I see the WRF-GFS has the airmass around 0 degrees Fahrenheit (-18deg C) by Monday morning at 5,000′ over the North Oregon Cascades…that’s really cold!  Last night and this morning’s ECMWF finally came into much closer agreement on the sequence of events over the weekend and early next week too, so that’s good news.

Seems like we’re aiming towards the middle of next week for a transition back into mild and wet westerly flow again.  It’s way too early to figure out exactly what’s going to happen.  Could be freezing rain or snow.  The GFS has gone several runs showing a quick punch of moisture up into our area on Wednesday.

Basically I feel more confident tonight that we are in for a good blast of cold air, definitely not historic though.  Maybe something similar to January 2007 when highs at PDX were only in the low-mid 30s before that “unscheduled” snowstorm arrived (I was in San Antonio…oops).  But I see nothing to produce snowfall until at least the middle of next week.  Okay, maybe flurries over the mountains Friday night, but that’s it.

Chief Meteorologist Mark Nelsen

221 Responses to Cold Blast 4 Days Away…

  1. goducks09 (Oatfield, OR) says:

    Yeah, not looking too good…
    Ugly run thus far.

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

    18z GFS so far has everything shifted east from 18z NAM and EURO. I’m not buying the GFS solution at all.

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

    Surface gradients
    As of 1 PM|Current|Hourly Change
    PDX-DLS: -7.7mb | 0.3mb Decrease
    TTD-DLS: -7.8mb | 0.6mb Decrease

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

    18z NAM Analysis

    Whether or not the NAM is a favored solution is probably not the point. The fact ii seems to closely match the EURO is. This run is quite a bit colder in the short term (To 84 hours)

    500mb ridge placement and orientation are more favorable. The NE flow and subsequent trough digs further west and farther offshore thus shifting the colder thickness values 510 and below farther west as well. Again I only decided to analyze the 18z NAM because of how it closely follows the EURO.


  5. Gordon says:

    Oregon Department of Agriculture
    Smoke Management Program
    Weather Outlook and Field Burning Advisory for Willamette Valley Growers and Fire Districts.

    Thursday, December 3rd, 2009 at 12:00pm.

    Burn Advisory:
    Agricultural burning is allowed. Suggested burn times are from now until 2:00pm.
    Stack burning is not allowed.

    Weather Discussion:
    An offshore upper-level ridge of high pressure is producing a dry northerly flow
    aloft over Washington and Oregon today. The freezing levels over western
    Oregon are way up around 10,000 feet. However, cool and dry low-level air has
    filtered southward, across the state. That is maintaining a strong low-level
    temperature inversion over the Willamette Valley.

    It was cold again this morning across the state with Willamette Valley
    minimums mostly in the 20s and low 30s. Eugene dipped down to 21 degrees.
    There were pockets of icy fog in the south valley earlier this morning, but
    skies were beginning to clear there at midday. Temperatures ranged from the
    low 30s, in the south valley, to the mid 40s in the north valley and along
    the coast. Most of western Oregon was getting some increase in high clouds,
    from a weak weather system moving into southwestern British Columbia.

    The ODA surface analysis showed pressures continuing to rise
    across eastern Washington and north-central Oregon, in
    response to the cool and dry Canadian air spilling into the
    region. That was combining with a weak thermal trough along
    the southern Oregon Coast to bring a dry offshore flow to
    western Oregon. Easterly winds were gusting as high as 20 mph along
    the central Oregon Coast and to over 30 mph at the western end of the
    Columbia Gorge. Western Oregon will see increasing high clouds this
    afternoon. Highs will likely stay in the mid 40s in the south valley but may
    reach the low 50s in parts of the north valley and along the coast.

    Surface Winds:
    N 5-10 this afternoon.
    Transport Winds:
    N 10 this afternoon.
    Atmospheric Ventilation Conditions:
    Maximum mixing height today will be near 2000 feet. Ventilation index 20.
    High Temperature:
    Salem’s high temperature today will be near 50.
    Minimum relative humidity will be near 33%.
    Salem sunset tonight: 4:32pm; sunrise tomorrow: 7:34am.

    Extended Outlook:
    A cool weather system is forecast to drop southward, across
    Washington and northern Oregon, late on Friday. It will
    have very limited moisture but will bring a chance of spotty
    light rain and snow to the region. Snow levels will rapidly
    drop to around 1000 feet, or lower, Saturday. An Arctic
    cold front is forecast to push southward across Washington
    and Oregon Saturday night and Sunday. That system is
    associated with very cold air but limited moisture. It
    should produce lots of clouds, and at least some snow
    flurries, as it pushes southward across the Willamette
    Valley Saturday night into Sunday morning. It is possible
    that some valley locations could pick up enough snow to
    cover the ground, but significant accumulations are unlikely.

    Quite cold and dry conditions will follow the Arctic cold
    frontal passage later Sunday through Tuesday. Cold easterly
    winds will increase in and near the Columbia River Gorge,
    making for very low windchill values. Overnight minimums
    will drop well into the 20s, across the Willamette Valley,
    Monday and Tuesday (locally into the high teens). Mostly
    sunny skies will help daytime highs recover into the 30s.

    A westerly flow aloft is forecast to undercut the offshore
    ridge and begin introducing moisture into western Oregon
    next Wednesday. With cold air in place across western
    Oregon, there is a high potential for significant snow
    and/or ice accumulation Wednesday and Thursday, before
    warmer Pacific air can penetrate inland. Temperatures will
    eventually moderate above freezing, from south to north
    across the Willamette Valley…most likely on Thursday. The
    last place to transition back to plain old rain will be
    areas in and near the Columbia River Gorge. Snow levels
    should lift to 4-5000 feet by Friday, with precipitation in
    the Gorge finally changing to all rain.

    Tomorrow (04 Dec): Increasing Clouds. Slight Chance of Light Rain or Flurries Late. 26/45

    Sat (05 Dec): Partly Cloudy. Increasing Clouds with Snow Flurries Late. 28/44

    Sun (06 Dec): Chance of Light Snow Early. Turning Partly Cloudy and Cold. 27/35

    Mon (07 Dec): Sunny and Cold. 20/33

    Tue (08 Dec): Sunny and Cold. 21/35

    Wed (09 Dec): Snow Developing Late. Possibly Turning to Freezing Rain or Rain South. 22/34

    Thu (10 Dec): Snow, Freezing Rain, or Rain…Turning to Rain From South to North. 32/44

    ODA Meteorologist

    Sounds good to me!

  6. WEATHERDAN says:

    The way the maps are setting up it looks to me to be a possible repeat of a snow situation that SLE had in mid Dec 1965. A quick burst of snow 2-4 inches. Then cold with some sun and some fog. Highs during that weeklong cold spell ranged from 28-37 degrees. With lows ranging from 19-29 degrees. And to those who worry that because it,s not cold enough east of the mountains right now. I can tell you from having followed the weather for about 45 years,that many times is has been very mild right up until the arctic front has passed through. Then the temperature dropped like a rock. As an example. In late December in 1968 during a Sunday the temp went from the low 40,s to the low 20,s in a space of 2 hours. The sky went from sunny with some cirrus clouds to cloudy with rain,to freezing rain,sleet,and then to snow. By Monday morning SLE had dropped to 8 degrees with over a foot of snow on the ground. So be patient.

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

    I like this!

    • Rob "Wrath" S.E. Portland says:

      This looks a lot more like the 12z EURO then the 12z GFS if you ask me in terms of the 500mb contours.

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

    18z NAM

    Hour 54
    500mb pattern

    Offshore block looks at this point a bit further northwest and amplified better.

    Compare to 12z NAM

    See the slight difference?

  9. Sandberg says:

    Is the EURO and the GFS on the same site?

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

    Surface gradients
    As of 12 PM|Current|Hourly Change
    PDX-DLS: -8.0mb | 0.1mb Increase
    TTD-DLS: -8.4mb | 0.4mb Increase

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

    Cold east wind can sure make the difference in temps.
    PDX is sitting at 46F
    I’m just now up to 40.5F

    This usually is the case when the east wind turns progressively colder you will see such a spread from PDX to areas east of I-205.

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