A Stormy Sunday Night Ahead

Now that the snow showed up as expected, we can move on to the next weather forecast issue.  A strong wind event or storm, depending on where you are located.

First, I’m amazed at how well the snow worked out this morning.  Almost everyone saw snow in the air, and we had some decent accumulations; 2-3″ up on Bald/Chehalem Mtns, I had 1″ or so at home, and many areas in the 500-1000′ elevation had at least “all-whiteness” for an hour or so.  Most important, mesoscale models absolutely nailed the sudden cooling atmosphere overhead with the steady precip band.  That was enough to change rain to snow in most areas.  And the timing (between 9-11am) was right on too.

We now have excellent agreement among the various models on what’s going to take place in the next 30 hours.  A developing low pressure system will deepen quickly as it heads towards the northwest tip of Washington.  It is forecast to reach somewhere between 972-980 millibars, then weaken quickly once it hits land.  All models look almost exactly like this at 4am Monday, the shiny new 00z ECMWF:

ecmwf_apcp_f36_nw

Several thoughts on this:

1. Pressure is nice and deep, but the low is beginning to fill as it heads inland.  If you want BIG wind, you want a system to still be deepening as it moves onshore.  That doesn’t mean you can’t get a damaging windstorm in this situation, but something to note.

2. Location of low pressure center is okay for a good wind event here in the Valley, but if we were expecting a significant windstorm, the low would need to be a bit closer, let’s say Hoquiam to Olympia or a little farther south.

3.  Pressure gradients are impressive with perfect isobar orientation (west-east) from sunset tomorrow through daybreak Monday.  Each model is different, but generally between 14-19 millibars EUG-OLM.  The old gauge for peak gusts in the north Willamette Valley is that gradient X 3.15.  That would give 45-60 mph gusts.  Interesting… 

4. I checked the Hannukah Eve Storm (2006), model forecasts were 20-22 mb in the same area.  That year we saw widespread gusts 45-60 mph in the metro area.  You may remember we were on the edge of that damaging storm, but even so, 250,000 PGE customers lost power at the height of the storm.  This storm should be weaker than that one.

5.  Model surface winds in the valley are not very impressive, BUT, I checked the blog entry just before the 2006 storm: http://fox12weather.wordpress.com/2006/12/13/windstorm_in_24/  That’s interesting isn’t it?  The same mesoscale models didn’t show real high winds in that case either.

6. The north coast really gets slammed by the “poisonous tail of the bent back occlusion” as the NWS says.  That is the surge of strong west-southwest wind whipping around the south side of the surface low.  This should happen around midnight tomorrow night.

So my forecast?

COAST:  Peak gusts 70-90 mph, two surges, one later tomorrow afternoon as the warm front passes, then the strongest as just mentioned around midnight tomorrow night.

INLAND VALLEYS:  Peak gusts 40-45 mph late tomorrow afternoon/evening, then 45-55 mph overnight tomorrow night.  If we actually see gusts around 50-55 mph at the official observing locations, we’re going to see 50-100,000 customers with outages.  How about we call it the POI (PGE Outage Index)?  So plan for at least brief power outages anytime tomorrow afternoon through daybreak Monday.

More snow Monday night and Tuesday?  It may be just barely cold enough, like this morning, but we might have a moisture limitation.  I sure wouldn’t say there’s a great chance to see sticking snow in the lowest elevations, but I’ll look at that more closely later; one exciting weather event at at time.

Chief Meteorologist Mark Nelsen

119 Responses to A Stormy Sunday Night Ahead

  1. cgavic says:

    Mark: you have to keep remembering where you live. The Columbia river gorge and its a affects. Naturally you would get snow like that. The further away from the gorge/east metro, the higher the snow level.
    At sandy at 1,100 ft. we only received moderate snow falling, but not sticking.

    I believe that difference in weather is due to your protection from SW wind, but increased east wind.

    I take a sister of whom I’m caregiver for, down to another sister’s place off of sturges ave., which is just before going down that hill to the refurbished downtown troutdale on the old Columbia river highway.

    We left sandy with s/SW winds blowing strong (I don’t have a wind station), I had to guide my sister to the car and help her in, and fight the wind to get in myself.

    20 minutes later, while the wind storm was still going, (looking on iPhone), when we got to my sister’s place on sturges, it was complete calm.

    Vs. another day when we had a slight east wind at the helm of our subdivision, we went through the same scenario. By the time we got to sturges ave. troutdale, I had to fight to get my sister inside the other house due to the “cold!” east wind swiping down on us.

    Completely different weather conditions and results.

    Just letting you know about the multiple climatic zones in northwest Oregon alone.

    Thanks.

  2. 18z NAM
    977mb(roughly) west of about Ocean Shores/Forks. NAM has been weaker than the GFS/WRF in handling the depth.

    Also, it now has an even stronger 300mb jet slamming into Oregon reaching well inland of 140-160kts!

  3. I’m even seeing darkening on IR Loop…. jeez…. dare I say it is similar to the stadium effect seen around an eye wall? Looks like it.

  4. Steve Pierce says:

    Potentially Damaging Windstorm on Tap For Tonight

    A potentially damaging windstorm is on tap for Salem, Portland and Vancouver tonight from 11pm to 6am. This mornings 12z forecast models are stronger yet with regards to this evenings windstorm forecasted for areas from Eugene to Vancouver and points northward. There is now forecast to be a 12-13mb pressure gradient from Eugene to Portland & Vancouver between 12 midnight and 3am as a deep low pressure crashes ashore on the Washington coastline. Coastal pressure gradients are forecast to be over 20mb from southern Oregon to Astoria on the north coast. This coupled with forecast models now clearly depicting the presence of a bent back occlusion sweeping through the Willamette Valley between 1-2am have increased the odds that a potentially damaging wind event is growing more likely tonight for NW Oregon and SW Washington. At this point, specific wind speeds are hard to pin down, but forecast models indicate that stronger winds just above the surface could mix down with the occlusion’s passage, resulting in winds gusting as high as 55-60mph in and around Portland just after midnight. Winds will likely be considerably stronger along the Oregon coastline. This setup has the potential to be the strongest windstorm since January 16th 2000 and December 14th 2006 when Portland recorded winds between 55-65mph in both storms. Additional concerns include rain soaked soil. With three months of above normal rainfall and the most rainfall in a single calendar year since 1996, trees will likely come down and power will be lost in wind prone areas tonight. I am preparing a complete / detailed update in the next few hours. If you live between Eugene and Kelso, as well as along the Oregon coast, prepare for this storms potential now!

    Steve Pierce
    President, Oregon Chapter of the American Meteorological Society (AMS)

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