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. ;)


Wednesday, September 24, 2014

Autumn Has Arrived

Wednesday, September 24, 2014
10:07 pm

Good evening everybody, I just got back from my first day of school. I'm actually pretty exhausted, so this will be a quickie. Only nine more months to go...

We officially had our Autumnal Equinox here in Seattle at 7:29 pm on Monday, September 22. I'm sure you all think you know how seasons work, but take some time and think about it, and I'm sure your confidence will fall. (haha, get it? fall? hahah I'm so funnnnyyyy)

The Earth takes 365.25 days to revolve around the sun. That's why we have a leap year every four years [(365 + 365 + 365 + 366)/4 = 365.25]. The Earth is also tilted at a 23.5 degree angle as it rotates in a more-or-less circular orbit (not perfectly circular, actually ellipsoidal, with the Earth being closer to the sun in the Northern Hemisphere winter). If we assume that our ellipse is a circle and the rotational speed of the Earth around the sun is constant, then due to the axial tilt of the Earth, one hemisphere will be pointed more directly at the sun, and the other one will receive more of a glancing blow. Check out the visuals below, a picture's worth a trillion words when trying to explain this stuff. Don't worry about the dates of the equinoxes not matching in the two pictures below; they can vary from year to year.

A Reason For The Seasons.

You can see that on the Northern Hemisphere summer solstice (June 21), the Northern Hemisphere is pointed toward the sun, and that the North Pole remains in sunshine all day long as the earth spins about its axis. Conversely, on December 21, the winter solstice for the Northern Hemisphere, the Northern Hemisphere is tilted away from the sun, and the Southern Hemisphere is tilted towards it. It's now Antarctica's turn to experience the midnight sun.

These two events happen when the sun is over the Tropic of Cancer (23° 26' N) and Tropic of Capricorn (23° 26' S), respectively. Somehow, the sun's gotta travel between these two places, so it crosses the equator twice a year doing so. These are the vernal (spring) and autumnal equinoxes. During these times, both hemispheres are equally pointed towards the sun, and the day is 12 hours long throughout the entire globe. Cool fact for math nerds: rate of change of day length varies sinusoidally throughout the year, with day lengths changing slowest at the solstices and fastest at the equinoxes.

The picture below shows the hours of daylight for different latitudes north of the equator and how they vary throughout the year. Note the sinusoidal shape, and the "midnight sun from June to mid-July at 70° N.

I love seasons, so if you have any more questions about seasons, throw 'em at me.

Weather-wise, the transition from fall to winter is much faster than winter to spring. In other words, we cool off faster than we warm up. And we sure got a early rainstorm to jump-start our autumn. It should be noted that "meteorological winter" here is actually the November-January period, even though geographical/astronomical winter goes through March, so it won't be long before it feels like winter. After this record-breaking summer, doesn't that sound a little abrupt? I sure think so.

Look at all the rain that fell from this past storm over the last 48 hours. The purples denote over two inches of rain. Sea-Tac got 1.54 inches. My weather station up on South Whidbey Island got 0.88 inches. And Sequim was dry.

Seattle RainWatch

Our winter is supposed to be warm and dry, but this is sure a way to kick off fall!


Thursday, September 18, 2014

Odile's Rain

Wednesday, September 17, 2014
5:54 pm

Hurricane Odile at peak intensity on 9/14/14 as a category 4 hurricane with 140 mph winds and a central pressure near 922 mb. 

Cabo San Lucas is your typical Baha-Californian tropical paradise (technically it's subtropical, but subtropical paradise just sounds... not as good as a tropical paradise, and Cabo San Lucas is about as exquisite as paradises come, so it deserves to be recognized as such). It is known for its fishing (never been there, but I really wanna catch a marlin), balnearios (Latin American resort towns), and scuba diving locations. If I had to guess, I'd also say it's known for its margaritas and continuous Jimmy Buffett songs playing outside open-aired bars. Jimmy Buffett's had a pretty powerful influence in resort towns.

One thing that Cabo is NOT known for are its major hurricanes. However, a couple days back, they experienced just that. Hurricane Odile slammed into Cabo San Lucas as a category 3 hurricane with 125 mph winds late Sunday, the strongest hurricane on record for the souhtern Baja Peninsula. That's as strong as Hurricane Katrina when it hit New Orleans.

Here's the track of the hurricane. Cabo is at the very southern tip of Baha California, which is on the Pacific side. As you can see, it experienced a direct hit from Odile. Odile started out as a tropical depression early September 10, as given by the blue triangles. Blue circles denote tropical storm strength, beige = category 1, light orange = category 2, darker orange = cat 3, and darkest orange = cat 4.

The track of Odile.

Odile caused a whole bunch of damage not just in Cabo, but the entire Baja Peninsula, and it degraded more slowly than your typical hurricane after encountering the mountainous terrain of Baja California.

Odile damage. Retrived from NASA.

Odile has now weakened to a "tropical rainstorm" with a central pressure of 1003 mb and sustained winds of 25 mph. However, don't let the pressure statistics fool you, as it is currently wreaking havoc on parts of the desert southwest. Chaparral, in Southern New Mexico, has already gotten over 3 ½ inches of rain, and amounts like these can be found throughout southern Arizona and New Mexico. Flash flood watches are in effect from southwest Arizona to southern New Mexico to extreme western Texas near El Paso for this event due to the heavy rainfall rates associated with the tropical low and embedded thunderstorms within it. Additionally, the topography of the area makes it even more prone to flash flooding, as the mountains simply act to collect all the rainfall into a valley and create a very fast-moving torrent of water... a flash flood. As if that wasn't enough, the dusty, arid landscape is not very conducive to absorbing rainfall, so any rain that does fall is more likely to end up in a stream instead of soaking into the soil.

As the below radar from the National Weather Service shows, the heaviest rainfall is currently centered over southwestern New Mexico. As the week goes on, this blob of rain will travel to the east, and places like central Texas will see some rain. However, as it does so, it will weaken, and places further east will receive less precipitation. This, combined with a change to flat topography and more grassy soils, should stamp out the flash flood threat in all but the heaviest thunderstorms.

Compliments to the NWS Doppler Radar National Mosaic

I start school on the 24th, so I have less than a week left of summer. I hope you can understand the lack of blogs, I've been too busy playing outside, trying to soak up these last precious moments of summer sunshine.


Friday, September 5, 2014

Summer's Last Stand?

Thursday, September 4, 2014
4:14 pm

Custer's Last Stand - Mort Kunstler

I had to do some refreshing on my American history to remember what Custer's Last Stand was. I did some research, and it turns out that this Custer guy really hated Indians, so he decided to fight some (specifically the Lakota, Northern Cheyenne, and Arapaho). He died. In fact, much of his puny cavalry died, as did his family. It was truly his Last Stand.

Do I think that Friday and Saturday will be weekend's last stand? No. Even though they will be extraordinarily nice, I've got a feeling that September as a whole going to be warm and sunny.

Let's take a look at our setup right now, at 8 pm (03z). The map below is very hard to see at the given size, so click on it to increase the resolution. The lines drawn are called isobars, and delineate lines of constant pressure. You can see a ridge of high pressure in the Eastern Pacific and a thermal trough centered over the Central Valley of California. Winds are generally coming from the north-northwest off the coast and from the north in the interior. This is a very typical summertime setup for the Pacific Northwest.

Retrieved from "surface analysis" @

Here's a look at the UW's WRF-GFS model 9 hours out from the 12z initialization this morning. Since it is so close to the initialization time, the large scale features are very similar to the analysis above. For all practical purposes, it just shows an alternative view of our setup.

In addition to showing the isobars, the above chart shows "thickness" contours. When the atmosphere is warmer, it becomes less dense, and the height between two levels of atmospheric pressure increases. This chart uses decameters and measures the thickness between 1000 and 500 mb. The larger the thickness, the less dense the atmosphere (and therefore the higher average temperature). As a side note, I often use thicknesses as a predictor of whether it is cold enough to snow in Seattle. I only start to seriously consider a snow when thicknesses drop below 522, and I'd rather have them in the 510s. There are exceptions of course (a relatively warm upper atmosphere with a cold lower atmosphere allowing thicknesses to be relatively high yet snow to still occur), but the 522 line is something respected by most meteorologists in the area.

As we go into the weekend, we are expected to warm up as the ridge to our west gets nudged to the southwest, weakens, and any onshore flow gets the boot. In its place, the thermal trough to our south will extend northward and open the door for warm, offshore flow to take hold over the Pacific Northwest.

Valid 08:00 pm PDT, Fri 05 Sep 2014 - 3hr Fcst   Retrieved from UW mm5rt Modeling Website

Sunday will be our warmest day, with highs reaching the mid to upper 80s. Highs will be even warmer near the foothills due to the adiabatic compression of air as sinks off the Cascades. In other words, the total amount of heat energy in the air does not change, but since a given mass of air takes up less space near sea level than at elevation, this energy is compressed into a smaller parcel of air. Therefore, no energy is exchanged from any separate parcels, but the air still changes in temperature. Pretty cool. Also, when air rises, it expands and the temperature cools, but the amount of energy stays the same

After Sunday, we will get a brief respite from the heat. I say "respite" because this 2-month period of July and August was the hottest in history, and I've not become acclimated to the heat; if anything, I've just been weakened by it. We could even see a little rain on Tuesday, but things clear up Wednesday, and a new ridge is back in full force by Thursday.

Valid 11:00 pm PDT, Thu 11 Sep 2014 - 150hr Fcst   Retrieved from UW mm5rt Modeling Website

This ridge won't extend quite as far up north, and the heights over our area will be slightly lower (567 instead of 570), meaning our temperatures will be lower as well (lower 80s if this scenario plays out). We should still have blazing sunshine though. For all intents and purposes, it will feel like our record breaking summer again.