Thursday, May 21, 2015

The Nepal Earthquake Part 1: Plate Tectonics

May 7, 2015
12:28 pm

I still remember the Nisqually Earthquake of 2001. Ironically enough, we had just finished an "earthquake drill" when our second-grade teacher shouted "Earthquake! For real!" We all immediately bolted under our desks, not necessarily because we were concerned about falling debris, but because we just liked bolting under desks. You could say it was a guilty pleasure of ours, I guess.

Many of those who have not been in an earthquake or who have not studied them equate them to the shaking and rattling of the Earth, but when I was under my desk, the movement seemed more akin to organized waves propagating throughout the room. When an earthquake occurs, it sends seismic waves from its hypocenter that travel thousands of miles per hour through the ground, so I have a feeling I was sensing the motion of these waves. It was actually pretty fun... I clearly remember having this vision of being in a boat on the water navigating through heavy seas, and these 'seas' were the seismic waves. Nothing was being damaged or falling down... it was just a little 15 second roller-coaster ride. Afterwards, we resumed school as if nothing had happened. The only place in Seattle that had sustained significant damage was Pioneer Square, which has old buildings that are not built to the same engineering standards as the other, more modern buildings in our area.

The Nisqually Earthquake may have been fun for 8-year-old Charlie, but the Nepal earthquake is horrible for everybody. There have been a number of severe earthquakes that the world has experienced over the past decade (Indonesia, Haiti, and Japan are just a few that come to mind), and the Nepal earthquake is right up there with them. Although it did not have the destructive tsunami that the earthquakes in Indonesia and Japan had, the damage that it has caused is simply unbelievable. Whole villages have been turned to rubble. Langtang Village, a small settlement of 435 people in the Langtang Valley north of Kathmandu, was buried under a landslide that, according to evewitness reports, was 2-3 kilometers wide and 100 meters deep. Seeing some of the destruction through pictures online makes me very sad, and I can't imagine how the friends and families of those affected must be feeling right now. A girl I grew up with and her friend are still missing from the quake and are presumed to have died (I wrote a blog post about it here), and the earthquake has directly impacted my community in a way I never thought it would.

I've always been not only a weather buff but an earth science buff in general, and that extends to geology. I think we can all agree that the Nepal Earthquake is terrible and we wish it never happened. But earthquakes themselves do not have any regard for life or property; they are just a natural consequence of plate tectonics. In that aspect, I think the Nepal Earthquake is a fascinating geological event, and that's what I'd like to blog about here since you hear so much about the death and destruction caused by the earthquake in the media. I hope you can join me in taking an interest in the geological nature of the earthquake and the processes that led to it.

This will be a three-part blog; the first part will explain some of the basics of plate tectonics, the second will explain the basics of earthquakes, and the third will look specifically at the earthquake in Nepal and how it compares to some recent earthquakes around the world.
____________________________________________________________________

Mt. Everest from Gokyo Ri, November 5, 2012. Retrieved from Wikimedia Commons.

In order to understand the Nepal earthquake, we first have to understand the geology of the Himalayas. The Himalayas are the world's tallest mountain range; out of the world's 10 tallest mountains, 9 reside in the Himalayas. The Himalayas are so tall for a variety of reasons, and not all of them are related to plate tectonics. They are young and located at low latitudes, and as such, they have not been heavily eroded by glaciers. The dominant reason why they are so tall, however, is due to the type of plate boundary that forms them... a continental-continental convergent boundary.

There are two general types of plates: oceanic plates and continental plates. Oceanic plates are thinner, denser, and comprised of basalt. Continental plates are thicker, less dense, and are mainly composed of granite. When one of these plates hits another plate, the less dense plate generally goes under the more dense plate. The characteristics of all plates are not the same, so some oceanic plates are denser than others, and the same is true for continental plates. There are many types of earthquakes, but the largest and most destructive ones are generally caused due to different plates smashing into each other. There are three kinds of these "convergent plate boundaries:" oceanic/oceanic, continental/oceanic, and continental/continental, so let's take a brief look at each of them and how they differ from each other.

The Aleutian Island chain is a great example of a convergent oceanic/oceanic plate boundary. The Pacific Plate is being subducted under the North American plate, creating a beautiful arc of volcanic islands and a deep ocean trench in the process. Note that the plates themselves are NOT the oceanic/continental crust; they are subdivisions of the lithosphere, which is the crust and the upper, rocky portion of the mantle. The movement of these plates is driven by convection currents on the asthenosphere, which, while still solid, is more viscous and deformable, and is liquid at certain locations, like mid-ocean ridges (more about those later).

Oceanic/oceanic convergent plate boundary. Retrieved from USGS.

Map of the Aleutian Trench and Islands. Retrieved from Wikipedia Page on Aleutian Trench.

The continental/oceanic convergent plate boundary is the one that we see along the West Coast of not only North America but South America as well. Our Cascades were formed by this plate boundary, and we will certainly have an extremely powerful earthquake within the next several hundred years, likely on par with the Japan earthquake back in 2011, and perhaps even stronger. The Andes are a textbook example of this type of plate boundary, as they have an extremely deep trench and very high (over 20,000 feet!) mountains in close proximity to each other. They have the strongest earthquakes in the world; the 1960 Nazca Earthquake was a 9.5 magnitude earthquake, which is approximately 800 times more powerful than our relatively puny Nisqually earthquake in 2001 (remember, earthquakes are measured on a logarithmic scale). These cataclysmic earthquakes are not just limited to continental-oceanic plate boundaries though, they occur at oceanic-oceanic convergent plate boundaries too. A 7.9 earthquake actually just struck the Aleutian Islands less than a year ago.

Continental/oceanic convergent plate boundary. Retrieved from USGS.

Continental-continental convergent boundaries create very high mountain regions for two reasons: no subduction takes place because the plates are too buoyant, and the plates have much more mass and are far thicker than oceanic plates. This leads to extremely high mountain ranges like the Himalayas of Nepal/Tibet and the Karakorum of Pakistan. These boundaries often create a massive plateau behind the main mountain range due to rock being pushed upwards instead of subducted. The Tibetan Plateau, which is five times the size of France and, on average, taller than Mt. Rainier, is a textbook example. These boundaries do not tend to have volcanoes and "megathrust" earthquakes (earthquakes approaching a magnitude of 9.0 or greater), but as we have seen in Nepal, they can still generate extremely powerful quakes.



Continental/continental convergent plate boundary. Retrieved from USGS.

These convergent boundaries are responsible for creating most of our mountain ranges. It makes sense intuitively; if you have a plate subducting underneath another, it's going to push that other plate up, and in the case of a continental-continental plate boundary, when subduction is not an option, the ground has nowhere to go but up!

As well as I'm discussing plate boundaries, I might as well briefly touch on the other two, divergent and transform, as earthquakes occur on all plate boundaries, not just convergent ones. Divergent plate boundaries arise when hot masses of the asthenosphere rise and burst through the lithosphere. This mass then cools, creating a new basalt crust and lithosphere. This formation of new lithosphere pushes each plate away from each other, causing them to diverge; hence the name divergent plate boundary.

Divergent plate boundary. Retrieved from USGS.


Ironically enough, divergent boundaries can create mountain ranges as well due to the magma rising through the lithosphere and cooling, forming a range. However, most of these ranges are underwater, because when plates diverge, seawater inevitably flows in after the rift between them has gotten large enough that seawater can flow through. Ever notice how the east coast of South America and west coast of Africa look like they fit with each other? Well, it is widely accepted that they were once connected in Pangea, which was a "supercontinent" composed of all the current continents, and that they began to break up 180 million years ago. In the middle of the Atlantic between these continents is the Mid-Atlantic Ridge. The Mid-Atlantic ridge is only one of many; the ocean is filled with these ridges.


Not all divergent plate boundaries occur underwater though. The East African Rift is a divergent boundary along equatorial Eastern Africa from Ethiopia to Malawi. There are several very deep lakes and stunning volcanoes in this area, including one that's becoming famous for its stark decrease in snow coverage (note: it's not due to global warming, it's due to deforestation).

Kilimanjaro's retreating glaciers. Credit: Penn State Department of Meteorology

Transform boundaries neither converge nor diverge; they slide right past each other. They differ from convergent and divergent boundaries in they are conservative plate boundaries, meaning lithosphere is neither created (divergent plate boundary) or destroyed (subduction zones). When plates are subducted or created, they are generally not done so in a uniform fashion, and rather have many individual transform faults connecting the overall subducting or diverging structure of the plate boundary itself. While they are most common around mid-ocean ridges, the most destructive ones occur near subduction zones on land. The San Andreas Fault in California is one of the most famous transform faults in the world, and is responsible for delivering many catastrophic earthquakes to the sunshine state.

The San Andreas Fault, an example of a transform boundary. Retrieved from USGS.

The San Andreas Fault has a striking structure and is something I would like to see in real life. Take a look at this photo below!

Aerial photo of the San Andreas Fault in the Carrizo Plain. Retrieved from Wikipedia

Southern California and Baja California are currently sliding northwards, and in approximately 50 million years, they will become subducted under the Aleutian Trench. So in the very very slight possibility that Los Angeles is still a bustling city 50 million years from now, citizens there will have to move somewhere else.

Charlie

Sunday, May 10, 2015

Tropical Storm "Dolphin" Near Pohnpei, Micronesia!

Saturday, May 9, 2015
11:46 pm

Me in a mangrove forest as part of a UW study abroad trip in Pohnpei, Micronesia during the summer of 2013.

Almost two years ago, I went on a UW study abroad trip to Pohnpei in the Federated States of Micronesia to learn about coastal ecosystems, and it was truly life-changing, in more ways than one. I had an amazing time while I was there, but I actually had seizures (I have epilepsy) and was ordered to leave prematurely by the UW. My mom got a free plane ride over as part of our travel insurance, and we traveled back, but not before spending over a week in Kona, Hawaii, and having amazing experiences there. We had really shoddy internet access while we were in Pohnpei, but I was still able to thoroughly document my experiences via blogs. If you look through the June/July blogs from 2013 (see the archive on the left), you'll see all my Micronesia and Hawaii posts. These are my favorite posts I've ever made - by a long shot.

Before I start, let me just clear up one misconception: "Micronesia" and the "Federated States of Micronesia (FSM)" are not the same. Micronesia is a geographic region encompassing tens of thousands of islands and 6 sovereign nations. Guam is in Micronesia. The Federated States of Micronesia are a group of four island states; from west to east (and, coincidentally, north to south), they are they are Yap, Chuuk, Pohnpei, and Kosrae. The coordinates range from 9.5° N, 138° E (Yap) to 5.3° N, 163.0° E (Kosrae). Pohnpei is around 6.8° N, 158° E.

One thing we talked about as soon as we got there was that Pohnpei rarely experienced hurricanes. The reason was its proximity to the equator. The Coriolis force, which causes everything from moving parcels of air to Felix Hernandez' devastating changeup to deflect to the right in the Northern Hemisphere and left in the Southern Hemisphere, is at a maximum at the poles and a minimum (zero) at the equator, so when you are within 5 degrees of the equator, air tends to not rotate around a storm, which is what you need for cyclogenesis.

One map that really shows this is a simple map of all the cyclones tracks from 1985-2005 over all ocean basins. You can clearly see that there are no cyclones forming within approximately 5 degrees of the equator. The black star I put on the map is the approximate location of Pohnpei. Notice how it is just on the edge of the area where cyclones start to form there, and that the cyclones that do impact it are generally pretty weak (stronger ones are in orange and red, weaker ones are in blue).

Data from the Joint Typhoon Warning Center and the NOAA. Retrieved from Wiki Commons

The above picture also clearly shows the 7 cyclone 'basins' - the North Atlantic, the Northeast Pacific, the Northwest Pacific, the Southwest Pacific, the Southwestern Indian, the Southeastern Indian, and the Northern Indian. The Northwest Pacific is by far the most active basin, averaging 26 cyclones a year. The North Atlantic Basin only averages 11.

The seven cyclone basins. Credit: NOAA

Let's take a look at what the satellite over Pohnpei looks like right now. This is the most recent visible satellite from the Aqua polar orbiter satellite, taken around 7 P.M. Sunday FSM time. Pohnpei is that small island in the middle.

Retrieved from NASA's Worldview Satellite Page

You can see there is a tropical storm - Tropical Storm Dolphin - that is really bearing down on Pohnpei. Thankfully, the maximum sustained winds are currently around 40 mph, barely tropical-storm-force. However, I wouldn't be as concerned about the winds or waves as I would be about the rain. Pohnpei is a very mountainous island, and heavy rains over the mountains could result in the inundation of piggeries in rural areas or flash flooding in cities that are within close proximity to rivers. Pohnpei is one of the wettest places on earth... the rainfall ranges from 140 inches per year near the airport to over 325 inches per year over the mountains. When I was there, I experienced some of this rainfall first-hand.

In fact, here's a little video I took of a rainstorm as it passed by while I was at our hotel on the Soundau Estuary.


Why does Pohnpei get extraordinary rainfall rates? It's because they get incredibly tall thunderstorms due to tons of heat energy and a very high tropopause. When a 70,000 foot cloud passes over you, you are going to get dumped on.


One more video... not only to show you how stunningly beautiful Pohnpei is, but how mountainous it is. Many islands in the Pacific are in danger of becoming completely submerged due to rising sea levels over the next century. Pohnpei is not one of them. These mountains significantly amplify precipitation not only due to orographic effects but due to upslope flow converging over the mountain peaks and causing convection over the mountains to cause those 70,000 foot thunderheads.

Meanwhile... we might get a few hundredths of an inch of rain on Monday. If you live between Olympia and Portland though, be on the lookout for some heavy rain Monday night and Tuesday night.

Enjoy the rest of your weekend!
Charlie

Wednesday, May 6, 2015

Major Tornado Near Norman

Tuesday, May 6, 2015
4:05 pm

I recently posted about several massive tornadoes and hailstorms in Texas. Well, it hasn't even been two weeks, but it looks like an even bigger tornado is bearing down on Norman,Oklahoma, a suburb 20 miles south of Oklahoma City. Norman is home to NOAA's NSSL (National Severe Storms Laboratory), and this is no accident, as they are ground zero for some of the most destructive tornadoes in the world. In fact, the strongest tornado ever recorded actually hit Moore, Oklahoma, another suburb of Oklahoma City that is about 10 miles north of Norman, in 1999. They had another extremely strong EF-5 tornado in 2013. I haven't heard any spotter reports yet, but just by looking at the radar, this tornado looks like it could be one of the strongest of the year. That's a pretty bold statement, but it's definitely not unreasonable when you look at some of the radar imagery coming in.

Radar showing hook echo, 9:45 pm CDT, April 26, 2015. Retrieved from Dallas-Fort Worth Scanner Twitter Page.

In my last post, we were talking about "hook echoes." Supercell thunderstorms are thunderstorms that have mesocyclones, or rotating updrafts, and the strongest of these supercells have a very prominent "hook" signature, where rain, hail, and debris are wrapped around this updraft. The picture above shows the hook echo from the storm I was following on my last blog, which was one of the best examples of a hook echo I had ever seen. That is, until I saw this image, taken 90 minutes ago.

Radar showing supercell with extremely well-defined hook echo heading towards Norman area. Credit: a Facebook thread.

Look at how tight that circulation hook is around the mesocyclone. I have never seen anything like that. This hook weakened momentarily, but strengthened right back up, and the tornado is continuing to move northeastward towards northern Norman/southern Moore. The following images were taken from GR2Analyst, which is a weather software that, while not free, is relatively cheap and extremely useful for analyzing severe weather.

Radar image at 5:50 pm CDT showing reformed hook echo heading towards Norman/Moore. The red polygon denotes the area under a tornado warning, the yellow diamond shows the tornado location.

Many of us have heard the term "Doppler Radar," but most of the images you see on TV have nothing to do with Doppler Radar. They simply give an approximation of how heavy the precipitation is by measuring the how much of the radar signal broadcast is reflected back to the radar site. Usually, the objects that do the reflecting are different types of precipitation, but they can be many different things. Back here, we sometimes see a radar signal at night even under clear skies due to birds migrating. In fact, as a little aside, let me show you a comparison between two radar images taken this past Sunday. The one at 8:45 pm has no signal (the stuff you see is just random noise), while the one at 09:52, just an hour later, is completely lit up. And it's all because of birds migrating north for the summer.

08:45 pm PDT, Sun 03 May 2015. Credit: UW Atmospheric Sciences Online Weather Data Archive

09:52 pm PDT, Sun 03 May 2015. Credit: UW Atmospheric Sciences Online Weather Data Archive

But back to Doppler Radar. All of the NWS radars across the countries are equipped with Doppler capabilities, meaning they can make use of the Doppler effect to find out the velocities of particles in the atmosphere and whether they are moving towards or away the radar. The Doppler Effect refers to how an object's apparent frequency to an observer is higher while approaching and lower while receding than its actual frequency. We've all experienced this with trains and ice cream trucks... as soon as they pass by, the pitch lowers. Doppler radars make use of this same effect, and are able to not only decipher whether an object is approaching or receding, but how fast it is moving. They make use of pulse-Doppler techniques, which are quite complicated and will be discussed in another blog.

In any event, the radar below shows a clear hook echo signature. Not only that; the velocities are extremely high. The maximum negative velocity (i.e. the max speed of the particles traveling away from the radar at Norman) is 124 knots, while the maximum positive velocity (the max speed of the particles towards the Norman radar) is 146.2 knots. These are incredibly high values, and are indicative of an extremely strong mesocyclone and tornado.

Doppler radar image taken around 6:05 pm CDT.

Other tornado warnings are continuing to pop up around the region, and I have a feeling we'll continue to see more tornadoes throughout the night. The latest warning from the NWS is for a "large and extremely dangerous tornado" near Lake Chickasha, which is around 30 miles west of Norman. If you have any friends or family in that region, alert them now. The entire region from northern Nebraska southward to central Texas is under a tornado watch until 9 pm and storms are continuing to fire up across the region. Let's hope that none of them hit any populated areas.

Charlie

Help for Sydney and Bailey

Tuesday, May 5, 2015
12:46 pm

Bailey Meola (left) and Sydney Schumacher (right). Photo credit: Scott Meola

The death toll from the Nepal Earthquake is now over 7,500 people.

It's just too hard to grasp... one minute, everything is calm and tranquil, and then, just 20 seconds later, thousands of people are dead and countless locales have been turned to rubble. There are very few things that can cause that much damage that quickly. The only glimpse of the destruction I have seen is through photographs on the web/in print and in videos posted during the earthquake that show structures that have stood for hundreds of years crumbling before your very eyes. It is a weird feeling looking on YouTube and seeing all this stuff, only to go on Facebook and see everybody's posts about everything ranging from the Pacquiao/Mayweather fight to what's happening in Baltimore. It just reminds me of how different the world we are living in is from the world the people in Nepal and adjacent countries are living in. It almost feels like we are on two different planets.

But things hit home for many of my friends and family when we got the news that two Seattle girls, Sydney Schumacher and Bailey Meola, were missing from the quake. They graduated from Garfield High School in 2014 and were taking a gap year before they went off to college. In a world where we immerse ourselves in technology, often at the expense of interpersonal communication, the girls wanted to take time to learn about other cultures, explore the great outdoors, and make relationships that would last a lifetime.

I went to Garfield and was in my senior year when Bailey and Sydney were freshmen. I never knew Bailey, but I've known Sydney ever since I was in kindergarten or first grade, as she is the younger sister of one of my elementary/high school friends, Paul Schumacher. That means I've known her for around 15 years. Paul, Sydney, and I all went to McGilvra Elementary, as did Paul's older brother, Will. When past classmates of Sydney's and former McGilvra parents heard of the devastating news, they were absolutely shocked. We all just assumed that the earthquake affected people we had no relation to, so when we heard that two kind and sweet girls that many of us had grown up with had gone missing from the earthquake, we were horrified.

Kyangjin Gompa in the Langtang Valley under gorgeous blue skies

The girls were hiking the Langtang Valley Trek at the time of the earthquake. Langtang Valley is only a few hours' drive from Kathmandu, but is very rural and strikingly beautiful. You can practically reach out and touch the majestic Himalayan Mountains as you stop at various tea huts and Buddhist monasteries on your trek. Paul took a similar trek two years ago, and he, Will, and Jay (his father) landed in Kathmandu on Friday and are now working with a private expedition team to try and find the two girls. The girls are thought to be somewhere near Kyangjin Gompa, a Buddhist monastery in the Langtang Valley. However, there is a possibility they hiked all the way to Langtang village, which is several hours away. Langtang Village was devastated by the earthquake and buried under a massive landslide, while Kyangjin Gompa escaped relatively unscathed. For now, all we can do is hope that they did not make the trek to Langtang Village.

Although the wait is horrible, and I can't even imagine the emotions the families of Sydney and Bailey are going through, it is truly amazing to see the outpouring of support for these two girls. A fundraising site here has already raised over 43,000 dollars for these two girls to go towards expenses for search efforts, with any extra money being donated to an organization providing earthquake relief in the region (ex: World Vision). Trees throughout Madison Park are wrapped in yellow ribbons, and there is a candlelight vigil at Madison Park Beach this Friday at 8:30 pm. The amount of yellow ribbons is overwhelming, and I believe that it is a reflection of their character. If you want to go to the vigil, let me know, and I'd be happy to provide some sort of transportation.

We have to be realistic and know that with each passing day, the possibility of finding these girls alive decreases. It hurts me dearly to type that. I just hope that no matter what, we can realize how much this has brought us together. As I said before, I don't have the privilege of knowing Bailey, but I can say without a shred of doubt that there would not be nearly as many yellow ribbons in Madison Park if Sydney wasn't the beautiful person she was.

Once again, the fundraising site is: https://life.indiegogo.com/fundraisers/help-bailey-and-sydney-in-nepal

- Charlie

Sunday, April 26, 2015

Hook Echoes, a Strong Texas Tornado, and Softball-Sized Hail

April 26, 2015
2:34 pm

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE FORT WORTH TX
436 PM CDT SUN APR 26 2015
TXC143-262200-
/O.CON.KFWD.TO.W.0007.000000T0000Z-150426T2200Z/
ERATH TX-
436 PM CDT SUN APR 26 2015

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 500 PM CDT FOR SOUTHERN
ERATH COUNTY...

AT 436 PM CDT...A LARGE TORNADO WAS LOCATED JUST SOUTH OF
DUBLIN...MOVING EAST AT 25 MPH.

THIS IS A PARTICULARLY DANGEROUS SITUATION.

HAZARD...DAMAGING TORNADO.

SOURCE...RADAR INDICATED ROTATION.

IMPACT...YOU ARE IN A LIFE THREATENING SITUATION. FLYING DEBRIS MAY
         BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE HOMES
         WILL BE DESTROYED. CONSIDERABLE DAMAGE TO
         HOMES...BUSINESSES AND VEHICLES IS LIKELY AND COMPLETE
         DESTRUCTION IS POSSIBLE.

THIS TORNADIC THUNDERSTORM WILL REMAIN OVER MAINLY RURAL AREAS OF
SOUTHERN ERATH COUNTY.

TORNADO...RADAR INDICATED
TORNADO DAMAGE THREAT...CONSIDERABLE
HAIL...4.25IN

_________________________________________________________________


The Earth has a lot of intense storm activity. Category five hurricanes can inundate cities and turn buildings to rubble. Lightning heats of the surrounding air to five times the surface of the sun, and creates a shockwave that can be heard for miles. Hailstones can weigh up to one kilogram, and cause billions of dollars of damage within less than an hour. But none of these can hold a candle to a category five tornado. Strong tornadoes are, without a doubt, the most terrifying and violent meteorological phenomena on a planet. Nothing else even comes close.

The U.S. doesn't get the strongest hurricanes (Philippines), the most lightning (Democratic Republic of the Congo), or the largest hailstones (Bangladesh), but we do get the most/strongest tornadoes. We get nearly all of our tornadoes east of the Rockies, but the majority of them occur in the Great Plains. In fact, so many of them occur there that the region has been given a name that has become ubiquitous throughout American culture. Tornado Alley.

I've been wondering when we'd see our next big tornado. Springtime is tornado time over Tornado Alley, but I just haven't seen that many tornado warnings popping up on the National Weather Service homepage this spring. I saw one today though, and when I took a look at the radar, I knew that this was not just some run-of-the-mill tornado. This was a damaging tornado, associated with an intense, supercell thunderstorm.

Fort Worth WSR-88D (Weather Service Radar 88D) image showing a strong tornadic supercell with a clear hook echo NE of Brownwood at 3:53 CDT. Retrieved from the Dallas/Fort Worth NWS Forecast Office.

I attached the picture above so that you could have a clear look at the actual radar imagery of the storm, but here's a picture below with the counties and warning zones highlighted. Yellow zones are severe thunderstorm warnings (hail of one inch in diameter or greater and wind speeds of 58 mph or greater), and red zones are tornado warnings.

Fort Worth WSR-88D (Weather Service Radar 88D) image showing a strong tornadic supercell with a clear hook echo NE of Brownwood at 3:53 CDT with counties and warning zones included. Retrieved from the Dallas/Fort Worth NWS Forecast Office.

So, how did I know that this storm was likely going to have a strong, damaging tornado? I knew so because the storm had a very clear hook echo.

Retrieved from NWS Storm Spotter Training

For a thunderstorm to be classified as a supercell, it can't just be massive, it has to rotate. Very few thunderstorms become supercell thunderstorms. The hook echo shown is produced by rain, hail, and in the case of a tornado, debris being wrapped around the supercell due to this rotation. One of the best examples of a hook echo was that of the 1999 F5 Bridge Creek-Moore Tornado, which was among the strongest every recorded. As you can see, the tornado was located right at the hook echo. Oh yeah, this storm produced the strongest winds ever measured on Earth at 301 mph. So yes, hook echoes aren't there just for show.

Retrieved from Wikipedia page on hook echoes

Thankfully, this storm that is currently going through will avoid the Dallas-Fort Worth metropolitan area, because if they were to receive 4.25 inch hail and a 'large, damaging' tornado, there could be over a billion dollars of damage and significant loss of life.

The latest update (530 PM CDT) says that although the tornado has ended, there is still 3-inch hail and 70 mph gusts with this storm. This is a very, very dangerous storm folks. If you want a tornado, you'll have to head down to Houston/Galveston. I'm not as worried about this one though, because the storm doesn't have a significant hook echo.

Houston WSR-88D (Weather Service Radar 88D) image showing a tornadic supercell headed ENE at 5:26 CDT with counties and warning zones included. Retrieved from the Houston NWS Forecast Office

Back here, there is a weak band of showers over the Olympics right now, so be prepared for the elements if you go outside tonight... you might get a tad wet. Don't forget to bring a towel!

UPDATE 8:00 PDT (10:00 CDT)

Look some of the latest pictures from the Dallas-Fort Worth scanner Twitter page. The below softball-sized hailstone was from the storm I talked above.

Photo credit: Zoey Rae James. Retrieved from Dallas-Fort Worth Scanner Twitter Page.

Also, they are now getting more tornadoes. The pictures below were also taken from their Twitter page. I bet you know where the tornado is! It looks like they do.

Radar showing hook echo, 9:39 pm CDT. Retrieved from Dallas-Fort Worth Scanner Twitter Page.

Radar showing hook echo, 9:45 pm CDT. Retrieved from Dallas-Fort Worth Scanner Twitter Page.

The National Weather Service is acting like they think this is a particularly strong tornado, perhaps even stronger than the one earlier today. As I said before, a strong hook echo is indicative of a strong tornado, and the hook echo on this storm is stunning.

THE NATIONAL WEATHER SERVICE IN FORT WORTH HAS ISSUED A

* TORNADO WARNING FOR...
  NORTHWESTERN HILL COUNTY IN CENTRAL TEXAS...
  SOUTHERN JOHNSON COUNTY IN NORTH CENTRAL TEXAS...

* UNTIL 1045 PM CDT

* AT 1010 PM CDT...A CONFIRMED LARGE AND EXTREMELY DANGEROUS TORNADO
  WAS LOCATED NEAR CLEBURNE STATE PARK...OR 9 MILES SOUTHWEST OF
  CLEBURNE...MOVING EAST AT 20 MPH.

  THIS IS A PARTICULARLY DANGEROUS SITUATION.

  HAZARD...DAMAGING TORNADO.

  SOURCE...WEATHER SPOTTERS CONFIRMED TORNADO.

  IMPACT...YOU ARE IN A LIFE THREATENING SITUATION. FLYING DEBRIS
           MAY BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE
           HOMES WILL BE DESTROYED. CONSIDERABLE DAMAGE TO
           HOMES...BUSINESSES AND VEHICLES IS LIKELY AND COMPLETE
           DESTRUCTION IS POSSIBLE.

Charlie