Saturday, October 25, 2014

Windstorm on the Way

Saturday, October 25, 2014
1:12 p.m.

First off, sorry for not being the most punctual poster as of late. I was actually recently contacted by the University of North Carolina of all places to write a weather blog using some of their graphics for WeatherOn. I really hope it will put uss "On" the map. Get it? :D

Anyway, you can check out the blog I wrote here.

But that post can be read anytime. We've got some action coming in right as I type this sentence, and things are starting to look pretty hairy around the Pacific Northwest.

Earlier this week, there was some talk about a windstorm impacting Oregon and Washington. This windstorm had the classic track of a "Sou'wester," (compare to Nor'easter) which is the slang term for the biggest region-wide windstorms we get in the Pacific Northwest, as they often come out of the southwest.

Image Credit: OWSC: Wolf Read's Storm King Website

We haven't had too many of these big Sou'westers lately. Our last one of note was January 16, 2000, but our last really big one was December 12, 1995. We had another big one back on November 13, 1981 as well. Still, none of these can compare to the granddaddy off all sou'westers, and in fact, the strongest extratropical storm to ever hit the United States: the Columbus Day storm of October 12, 1962. Some call it the CDS, some call it simply "The Big Blow," and others, like myself, prefer the unnecessarily verbose "Terrible Tempest the Twelveth." Either way, the Columbus Day Storm was a sou'wester on a whole other level, and a storm a likes of which we will not see for centuries, even millennium. It truly was a singularity, and it still casts a dark shadow over every other single storm to hit the Pacific Northwest. Many of them have been very memorable, but none of them have caused such widespread destruction over such a wide area. I would give an arm and a leg to see what that beast looked like on satellite, but alas, there were no satellite shots taken of it. The sad thing is that I'm not necessarily joking when I say I'd give an arm and a leg... I'd just be taking one for the team. I'd have to ponder over it.

You'll notice that two of Seattle's largest windstorms - the Inaugural Day Windstorm of 1993, and the Hanukkah Eve Storm of 2006, are not listed. The reason for this is that they are not sou'westers in the first place. They approached the coast from a more western track instead of paralleling the coastline. If they did parallel the coastline, they would have impacted a much larger amount of inhabited land, and the damage totals would have been much higher.

The three major cyclones I just mentioned - 1962, 1981, and 1995, were all below 960 mb, which is about equivalent to the pressure of a category 3 hurricane. This cyclone is predicted to drop to around 985 mb. Accordingly, the winds will be much less, but it has already taken a track of a region-wide windstorm and affected a large area, and it is on a course to provide particularly high winds to the Seattle metro area as it passes just to the north of it. Winds are already picking up here right now.

Take a look at the rooftop data from the UW atmospheric sciences building. In particular, take note of now the winds have strongly increased just in the past hour. And folks, they are only going to get stronger.

Atmospheric Sciences Building 24-hour rooftop summary

Taking a look at our current satellite, you can see that the low pressure is just starting to make landfall into Western Washington. Oregon is still seeing strong winds, but the strongest ones are likely over. Winds will hang on a little longer in northern Oregon.

5pm UW Infrared Satellite

Additionally, here are the warnings and watches in effect for Western Washington and Western Oregon. It's not often that you see tan in the Puget Sound area, especially in October.

NWS Seattle

NWS Portland

The effects of this windstorm could be exaggerated by the fact that the deciduous trees still have the majority of their leaves on them (at least they do right now!). More leaves = more surface area, and a higher surface area will catch more of the force of the wind gusts and transfer that force to the tree, making it more likely to snap or topple. In addition, our soil is relatively saturated due to that massive rainstorm we saw earlier this week, and since saturated soil loses its cohesion, it is easier for complete tree failures to occur in the presence of it. As if all this wasn't enough, there have been weak and dead branches that have stayed in the trees all summer long, and being the first windstorm of the season, this one is the one that is most likely to blow them all off. Don't be startled if you lose your power tonight.

Thank you! Stay safe!

Friday, October 10, 2014

Is El Nino Making A Comeback?

Friday, October 10, 2014
5:08 pm

After a return to neutral conditions over the summer, we will likely see weak El Nino conditions for the 2014-2015 winter.

At least that's my prediction. And I will tell you why.

There's a wonderful, wonderful website hosted by the National Weather Service's Climate Prediction Center that you can access right here, and it is an animation of the current sea-surface-temperatures in the tropical Pacific. As I'm sure many of you know, the tropical Pacific is where the single most influential short-term atmospheric/oceanic oscillation occurs. El Nino, and its sister phase, La Nina, influence weather throughout the world. And it looks as though after teetering on the edge of an El Nino, we may finally enter one in the near future.

Before we take a look at how the SST have evolved over the past few months, lets review our El Nino "regions."

Retrieved from the National Climatic Data Center

Atmospheric scientists and oceanographers refer to certain regions when talking about SST in the tropical Pacific. For example, they might say "temperatures were 1 degree Celsius above average in Nino 1+2, and 0.7 degrees Celsius above average in Nino 3.4."  Nino 3.4 is the most commonly cited region, and El Nino conditions are often classified as anomalies of 0.5 degrees C or above in Nino 3.4. 

Now, we can take a look at the SST traces.

ENSO Discussion

You can see that we had neutral conditions until May in most locations, after which we turned slightly El Nino. By August though, things were on the decline, and we have been in borderline El Nino conditions ever since. However, if you will recall that SST animation link I gave you above, the most recent charts show an increase in warm water in the eastern Pacific, particularly in Nino 1+2. The water that upwells off Peru propagates westward, meaning it won't be long before this newly-formed poll of warm water ends up in Nino 3.4. The big "blob" of warm water in the Northern Hemisphere north of Hawaii is related to the Northeast Pacific Mode (NEPM), and I shall talk about it in a different blog.

ENSO Discussion

In addition, the CPC and IRI (International Research Institute for Climate and Society) have climate models that predict whether ENSO will occur or not. These models are far from perfect... they originally predicted that this year would feature a very strong El Nino rivaling the 1997-1998 El Nino event, which was the strongest on record, though an El Nino from 1982-1983 was very strong as well. Instead, now models are leaning towards a weak El Nino, with some not even developing an El Nino. The CPC lists a 2/3 chance of an El Nino developing within the next 4-8 weeks and continuing into next spring. As I said before, based on the latest SST profiles from the tropical Pacific, I believe that we will see a weak El Nino this winter.

ENSO Discussion

Alright, enough of this tropical Pacific stuff. What's in it for us, here in the Pacific Northwest?

Below are some diagrams of patterns associated with El Nino and La Nina (which, by the way, describes cooler than average SST in the tropical Pacific). With El Nino, the Pacific Northwest is often warm and dry, while California gets clobbered with big storms. Los Angeles had F2 tornados in 1983 and 1998, both strong El Ninos. Coincidence? I think NOT!

Climate Prediction Center

Many people may welcome a warm and dry winter, but I certainly do not. I like my winters to be dark, rainy, stormy, and above all, snowy. However, even El Nino winters can feature snow, particularly weak ones. In fact, our snowiest winter ever occurred during an El Nino winter. December 1968 and January 1969 combined for an astonishing 67.5 inches of snow (thank you Scott Sistek for that statistic). Scott wrote an excellent blog on this; you can read it here.

We don't have any snow data for the 1997-1998 winter, but the snowfall accumulation for 1982-1983? "Trace." If we had a strong El Nino, I'd abandon all hope now, but history tells us that we aren't completely out of the snow game yet. Not by a long shot.

Long range forecasts keep us warm and dry. The thing is, long range forecasts have always been keeping us warm and dry since El Nino started to appear, yet July, August, and September were all wetter than normal, primarily due to heavy precipitation events. As we all know, they were all much hotter than normal, making for a spectacular summer. I personally hope that we go the way of 1968-1969, and even if we can't get 6 1/2 feet of snow in the lowlands, we can try and get a significant amount in the mountains for winter recreational activities and water storage purposes.

With a weak El Nino, you never know what can happen. ;)