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.


Wednesday, September 3, 2014

A Convergence Zone to End All Convergence Zones

Wednesday, September 3, 20142:14 pm

Someday, somehow...

Sorry, I was listening to Nickelback. But that question has often graced my mind when thinking about convergence zones. I've been wondering when we'd get a "zone to end all zones," and this is the best one since the morning of December 18, 2008. I don't think anything can top that one... I got 4-6 inches of snow and school was canceled. Our house also almost got struck by lightning around 5 a.m. It was bloody fantastic. That convergence zone represented the leading edge of the arctic air mass that settled in afterwards for nearly a week and wreaked havoc over the entire city.

05:08 am PST, Thu 18 Dec 2008

This zone, while not snowy and having quite as vicious lightning, had much heavier precipitation and much more lightning to go with it. Let's take a look at some screenshots at certain times, and then some animations of the entire evolution of the convergence zone as a whole. All of these were retrieved from the UW Atmos Online Weather Data Archive.

04:40 pm PDT, Tue 02 Sep 2014

We started out with a strong squall line heading through Snohomish and Skagit Counties. It even had the signature of a "bow echo," something commonly associated with very strong squall lines and mesoscale convective systems over the Great Plains, and something that is generally indicative of very high straight-line winds.

05:25 pm PDT, Tue 02 Sep 2014

45 minutes later, the squall line turned southeast and weakened.

05:59 pm PDT, Tue 02 Sep 2014

30 minutes later, we see more of a SW-to-NE oriented convergence zone begin to develop. The area of rain begins to broaden, and it continues to move southward. Northern Seattle is getting thunder and lightning.

06:57 pm PDT, Tue 02 Sep 2014

By 7, much of downtown has gotten thunder and lightning or is getting some at the moment. The real action, however, is further east. The zone becomes more east-west oriented.

07:26 pm PDT, Tue 02 Sep 2014

By now, only a few select places west of Lake Washington are getting hammered with precip. The vast majority of precipitation is falling east of the lake.

08:57 pm PDT, Tue 02 Sep 2014

Later on that evening, a secondary zone developed over Seattle as the main zone moved further southward.

Here are some animations.



The thing about convective precipitation (precipitation driven by rising air and instability) is that it is much more localized than the stratiform precipitation we usually get around here during our fall and winter months when our great Pacific storms roll in. Take a look at Seattle's Rainwatch rainfall estimates, and notice how much the precipitation varies based on your location. This is over the past 48 hours, but keep in mind that most of this precipitation fell within the space of just a few hours. Some places got the majority of their rain in a few minutes.

Retrieved from Seattle RainWatch

Over 6 inches east of Maple Valley! Simply incredible. Meanwhile, places like Mountlake Terrace hardly got anything.  That's how thunderstorms work.

Unfortunately, I can’t show any pictures of the flooding that occurred around the area because all the ones I’ve found are from commercial websites and I don't have copyright permissions. I've emailed a site to ask where I can find some ones available for public use/if I can use some of theirs. If I get my hands on some pictures, I'll put them up!


Tuesday, August 26, 2014

Here Comes The Rain

Tuesday, August 26, 2014
7:30 p.m.

Here comes the sun... not. 

Although you wouldn't know it, we are actually well above average for rainfall this month (and, come to think of it last month was above average in the rainfall department as well). This is due to Sea-Tac accumulating 0.50 inches of rain on the 12th and 0.85 inches on the 13th. We've tallied up a grand total of 1.43 inches of rain at Sea-Tac the entire month, but seeing as 1.35 inches fell in two days, you wouldn't know that we are so much above average. Average for this time of month is 0.67 inches.

At the end of this week and into next week, we actually will have a pattern change which will bring us more rain. However, this rain will come to us in a more familiar fashion with periods of light rain as opposed to heavy downpours from convective activity. Before that though, we've got some warm weather to go through.

Tuesday got up to 88 at Sea-Tac, and Wednesday, while cooler, should still be pretty darn hot.

Valid 08:00 pm PDT, Tue 26 Aug 2014 - 3hr Fcst: Taken from the UW mm5rt website.

As you can see, there is a ridge of high pressure over us, but it is moving east and will continue to do so. As it does so, the door will be opened to a cooler, moister Pacific flow. I'd expect temperatures to climb into the mid 80s across much of Western Washington Wednesday with high 70s directly by the Sound, but Thursday and Friday will feature increasingly cloudy conditions with highs in the mid 70s, particularly in the mornings as a marine layer off the ocean settles in overnight and thins throughout the day. Don't be surprised if you feel some drizzle in the mornings these days if there is a particularly strong marine push, particularly on Friday.

As for the rain, a small amount might stick around the Seattle area Thursday night as a very weak feature comes through, but most of it looks to roll through Saturday afternoon.

Valid 02:00 pm PDT, Sat 30 Aug 2014 - 93hr Fcst: Taken from the UW mm5rt website.

As you can see, the rain shown above is pretty negligible. The GFS shows a stronger system coming in Monday night though, and it could bring heavier amounts of rainfall. That being said, the European model, which is generally more accurate, predicts a drying trend after the weekend.

Valid 05:00 am PDT, Mon 01 Sep 2014 - 132hr Fcst: Taken from the UW mm5rt website.

Will we follow the GFS' predictions, or will we tailor more closely to the Euro? It's too far away to tell at this point, and the models have not been very consistent run-to-run. For example, the Saturday system was much stronger on Tuesday morning's GFS than the run Tuesday night.

Either way, I don't think we'll be seeing much in the way of wildfires for a while. :)


Saturday, August 23, 2014

Bárðarbunga - Is a Major Volcanic Eruption In The Cards?

Thursday, August 22, 201411:05 p.m.

Bárðarbunga releasing steam from beneath the Vatnajökull Glacier. Photo Credit: Oddur Sigurdsson, Iceland Geological Survey. 

It's safe to say that Iceland's remote Bárðarbunga volcano doesn't look like a typical volcano. Even though it is 6,591 feet tall, it has all but been completely consumed by the massive Vatnajökull glacier, with the only evidence of a volcano being a snow-covered caldera with a tiny hole in the center formed by warm gases melting snow as they travel from the volcano into the atmosphere.

Isn't it cute? Photo link:

But the above dimple is far from docile. Bárðarbunga has had major eruptions in the past, and it looks as though another one may be in the cards. We have many things to talk about, but before I go any further, let me explain what's been happening recently with the daintily cute aforementioned volcano.

Bárðarbunga has been the site of a vast swarm of earthquakes recently, with the strongest one (magnitude 4.7)  occurring around 18 hours ago at midnight 8/22/2014 Iceland time. Swarms of earthquakes are often a precursor to volcanic activity... Mt. St. Helens was having hundreds of small earthquakes a day before it finally blew its top on 8:32 a.m., May 18, 1980. Between last Saturday morning and Monday evening, the Iceland Meteorological Society measured 2,600 earthquakes, with that 4.7 earthquake being the biggest one measured since 1996.

So far, no magma has made it to the surface, but scientists are concerned that these earthquakes may signal an impending eruption. Even though it has been found that earthquake swarms lead to eruptions less than 10% of the time, a Bárðarbunga eruption could paralyze not only Iceland but all of Europe.

First, let's talk about the anatomy of this volcano.

It lies under the northwestern edge of the Vatnajökull glacier, and, as I said before, is completely encased in ice. You are not able to see the structure of the mountain. At the rate we are warming up, several generations south of us will surely be able to see parts of the mountain, but we don't live in a world that has truly felt the effects of anthropogenic greenhouse gas emissions.

Some of you may remember the eruption of the volcano Eyjafjallajökull (aka: "that Iceland volcano") back in 2010. While Bárðarbunga is easier to pronounce (the anglophone spelling is "Bardarbunga"), they share many similarities, as they have comparable geological properties and are both covered in ice. The difference is that  Bárðarbunga is much bigger, and if it does erupt, it will release far more magma.

8,500 years BP,  Bárðarbunga released 21-30 cubic kilometers of lava and covered 950 square miles with it. This is speculated to have been the largest lava flow of the Holocene Era, which began at 11,700 years BP (right after the last ice age) and continues today. The Vatnaöldur eruption of 870 was very large, as was the Veiðivötn eruption in 1480. Bárðarbunga hasn't witnessed an actual eruption since 1862, though it did have some activity in 1996.

So what are the consequences of a possible eruption?

Well, the biggest local consequences will be the threat of massive flooding. A large eruption would melt an incredible amount of water, and this water could sweep villages away. These "volcanic floods" are not unique to Icelandic volcanoes; they occurred as Mt. St. Helens melted snow in 1980 and are actually one of the biggest threats to nearby towns in the event of a Mt. Rainier eruption.

Something with a far broader geographic scope would be the ejection of ash into the atmosphere. Remember the Eyjafjallajökull volcano I was talking about earlier? The 2010 eruptions of it led to the highest travel disruption in Western Europe since World War II. The eruption truly was small... the ash cloud only reached 10 kilometers high, and only 270 million cubic meters of ash was ejected into the atmosphere. Mt. Pinatubo, for instance, ejected 10 billion cubic meters of ash 34 kilometers high. What made Eyjafjallajökull so much more destructive?

Eyjafjallajökull erupting on April 18, 2010.ökull

First off, it's important to remember that Iceland is right between the U.S. and Europe, so it is important as a hub for air travel. But there are other geological factors at work. When the magma at Eyjafjallajökull's vent reacted with the nearby glaciers and rapidly cooled, it contracted into much smaller and more jagged/porous ash particles than are usually seen. Moreover, more fine ash was created when small gas bubbles in the molten rock expanded as the magma rose and approached the surface. The median width of all the ash grains was found to be less than 1 millimeter wide, and further away from the vent, 20% of the ash particles were smaller than 16 microns, which is approximately six times thinner than a human hair. In the process of cooling rapidly as it rose, the  Because this ash was so light and, due to its rough and porous texture, was aerodynamically favored to stay high in the atmosphere for a long time, massive air travel disruptions resulted. There was also a fairly stagnant weather pattern over Western Europe at the time, so these particles were not carried laterally either. They just sat there and wreaked 1.7 billion dollars worth of havoc on the airline industry.

Canceled flights at Leeds Bradford Int'l Airport.ökull_eruption

If Bárðarbunga were to erupt, it would be in that same jet path, and the ash particles would probably have similar characteristics and be FAR more numerous. The weather would be the wild card.

By the way, Bárðarbunga was recently just updated to a "orange" risk level, which is apparently the highest there is without a volcano already erupting. They updated it after they found out that, in addition to all these earthquakes continuing to happen, the magma is moving closer to the surface.

When I was little, I loved volcanoes more than anything else. I've now given my heart to weather, but my love for volcanoes is still very alive.

Update: 8/23/2014

Bárðarbunga started erupting this morning for the first time. The eruption is small, and it is being extremely carefully monitored.


Friday, August 22, 2014

Marine Pushes, and Their Effect on Summer High Temperatures

Thursday, August 21, 2014
11:03 p.m.

We "only" reached 70 degrees today. At 6 degrees below average for a high temperature, it's fairly cool, but not extraordinarily so. The last time we didn't hit 70 was on July 24th, meaning it's been nearly a month of consecutive 70 degree-or-higher days, with some days much higher (Sea-Tac hit 96 on August 11). That's pretty impressive.

We may have kept our streak going, but setting a new record for consecutive days above 70 is not going to be easy. The record is 61 days (thanks Scott Sistek), so we'd have to keep our streak going into the end of September to set a new one. It'd be pretty amazing if we broke that record, but the chances of doing such a thing are next to nil.

Why did we have such a downward shift in temperatures today? It's not like we had any massive rainstorm come through the area or anything. Besides, even on August 13, our rainiest day of the summer (0.85 inches at Sea-Tac), the temperature got up to 74 degrees. What made this day different.

The answer, my friends, lies in the all-too-familiar phenomenon we call the marine push. Also known as our "natural air conditioning," it occurs when pressure over land is lower than that over the ocean, and cool, moist maritime air flows into Western Washington. Strong marine pushes generally are associated with thick stratiform cloud decks extending into Western Washington all the way to the foothills of the Cascades. As the day goes on, the sun often "burns through" these clouds, but if the push is thick enough, the sun won't be able to disseminate the stratus clouds, and the surface won't heat up as much as a result. Those are the types of pushes that give you particularly cool days, sometimes as much as 10 degrees below average.

Let's take a look at the marine push event that occurred today. All of these images were gotten from the UW weather loops website. It's a great website with satellite, radar, and model loops and time series of general observations throughout our area. They even have lightning strike data available. In addition, they have an archive of tons of previous satellite and radar images, so you can look at all your favorite storms from the past. I've relived many a storm through this awesome feature.

10:00 a.m.

11:00 a.m.

12:00 p.m.

12:45 p.m.

2:00 p.m.

3:00 p.m.

You can see that it took a while for the clouds to clear out. At 10:00 a.m., they were widespread throughout Western Washington and spread far into the Cascade foothills. They gradually declined in extent and depth, and were gone completely by 3:00 p.m. It wasn't the strongest marine push of all time, but it was enough to cause a cloudy morning.

This coming week looks to feature a decrease in the magnitude of these pushes, and by early next week, they may not be happening at all. However, these pushes will return later in the week, and we will cool down again as a result.