Monday, December 8, 2014

Is a Major Windstorm Headed for the Northwest?

For the last few forecast cycles, the U.S. global model, the GFS, has been predicting that a very strong Pacific storm will develop off of northern California and then slam into the Pacific Northwest on Thursday.

But there were reasons to be wary about this forecast.  The European Center model, which is usually superior to the U.S. GFS, had no such strong cyclone.  Other modeling centers have found different solutions from the GFS (weaker storm) Furthermore, the U.S. model had the position and intensity of the system varying substantially.

But tonight's forecast is highly consistent with those made earlier today, and the forecast solution of other major centers, such as the UKMET office are now doing something similar.

Finally, we are now only 48h out and it is unusual to have major forecast failures at that time range. But it is also unusual for there to be such major discrepancies between major models this close in.

Let's start by looking at the latest sequence of 12-km UW WRF runs, driven by the National Weather Service GFS model. These are surface charts with the lines being pressure lines (isobars).

10 PM Wed. you see a 982 hPa (mb) low off of northern CA

 By 4 AM Thursday it had deepened (975 hPa).  That is a very deep low center for our neighborhood.
Intense pressure difference (gradient) to the south and east of the low.  Big winds.

 By 10 AM Thursday the low had weakened a bit (976 hPa) and hurricane-force winds are hitting the northern Oregon coast.   This is very serious stuff.

 And then the system weakens substantially as it crosses Vancouver Island Thursday afternoon (4 PM is shown). Strong winds over Puget Sound (30-50 mph gusts perhaps)

Just a small shift in the storm or how it revs up could greatly change the details of this forecast, so PLEASE keep this uncertainty in mind.

Take a look at the model wind gust forecast for 8 AM on Thursday.  How many ways can you say amazing?  75 knot gusts and more.  We are talking about power outages and damage on the Oregon coast.

The UK MET office model, which is the second best in the world, is now going for a storm, but a weaker one.  Here is the forecast for 4 PM Thursday.  A 983 hPa low on the WA coast.   A bit different solution and not as strong.

The Canadian Meteorological Center (CMC) GEM model, the fourth best in the world is NOT producing a storm:

At the same time, the European Center model, normally the most skillful, has weaker low center  (988 hPa) over SW Washington (shading is relative humidity, solid lines are pressure)

This is a small storm, with substantial uncertainty remaining, but we need to watch it carefully.  But tomorrow night we should have much more confidence about what will happen.

And we should not forget the HUGE amount of rainfall that will fall in the next 72 hr ( see forecast). 5-10 inches in the Olympics, on Vancouver Island, and the southern Coast Mountains.  Huge amounts in norther CA.

As a result, the NWS River Forecast Center is going for flooding on several western WA rivers, some reaching moderate flood levels.  And there is the potential for some landslides.


Jon Preston said...

Wow! the point forecast for Cape Blanco, OR is near epic for Wednesday.

JewelyaZ said...

Letting my friends with a beach house in Astoria know... thanks for the update!

Michael Snyder said...


So if Im correct the danger here is this:

With any mid latitude cyclone along our coast, the stronger the low tends to be, the more northward it turns.

So since the Euro and other models have a weaker low moving in south of us, the uncertainty would be if they are in error and the low ends up being deeper than forecast it would bring a fairly powerful low right in a favored high wind event for the Puget Sound.

Is this how you view this event as well?

Senge said...

Wasn't there a big wind event about 18 years ago right about this time? I recall friends worrying about whether the power would get restored in time for their Christmas parties the week before Christmas ...
(In the Portland,OR area)

Spiritchaser said...

Hi Cliff,

Looking at the WRF-GFS run (4 km): That modelled low is tracking north at about 40 kt, not quite as fast as the Columbus Day Storm, but certainly with some momentum, and a feature that would help support strong S winds. However, as you mention, the storm appears quite compact. This appears partly related to the higher central pressure than the major classic events (e.g. 12 Oct 1962, 14 Nov 1981, 12 Dec 1995). Deeper central pressures appear to be correlated with broader high-wind fields. The compact nature makes track critical--slight variation can have significant changes in outcome for particular regions, especially in the interior. Keep in mind 10 Nov 1975, a compact storm that tracked into southwest OR. Or 27 Mar 1963. In any event, I will be watching this storm closely.

-best, Wolf

Autumn Leaf - Robert Scott said...

Prof. Mass-

Can you give some correlation to the track of Thursday's low pressure along the coast as to the strength of the wind for the interior. I recall something that was mentioned some time ago regarding the track of other strong wind events.

windlover said...

Senge....I believe it was December 14, 2006 when we had our last big widespread windstorm. I love windstorms but worry about those with trees close to their homes and those who have no alternate heating source if the power goes out....As for me? Bring it on!!!

Unknown said...

Senge, it was 8 years ago. I'm hoping it won't be as bad as that one, or the Inaugurational Day storm in 1993. But, guess we'll see.

VS said...

In the NW this weather happens more often than not...In SF it was told there was a 'potential" for a serious storm. Since it is a rarity here, then better safe than sorry...did you forget the two ATL Ice storms earlier this year? The first caused havoc as nobody listen to the "potential" problems. Two weeks later the same type of ice storm hit and EVERYBODY listened and imagine that, no havoc. When people don't prepare for a "potential" problem thats when problems happen.

Rhonda Fergerson said...

my home of 21 years was totaled by a 100 year old healthy oak tree that was ripped up by a micro-burst, it tossed that beautiful tree onto my home with my mom and dad inside. thank god they weren't seriously hurt. we are still waiting to move into our new home. I had never experienced anything like that weather,,,ever! there was warm wind and cold wind and the clouds were breathtaking. it seemed very unnatural to me, to have a such a thing happen in oregon.