Tranquil Weather to Continue

Saturday, August 6, 2011
12:52 A.M. (up late)

When storms come our way, I usually look at multiple weather models, because they all show different outcomes from the same set of present conditions. Sometimes these different outcomes are pretty similar, and other times, they are completely out of sync. When there is an especially tricky situation for the models to handle (such as a moderately-sized windstorm or a lowland snow event), events can change drastically from each iteration of the same model. This is especially common as forecast time increases, as the models become much less accurate due to the magnification of the approximations made after the input data goes in (I will talk about this some other time/search the blog for a post on it... I may have done it before).

However, when there are calm times like these, I use one model over all of the others because it is easy and it usually works. This is the "Extended WRF-GFS Model" from the UW, which can be found here: http://www.atmos.washington.edu/mm5rt/extendedgfsinit.html.

I've looked over this model for several days, and it has been pretty consistent in continuing the trend of cloudy mornings and bright afternoons. Some mornings are more cloudy than others; today only got to 66 degrees in downtown Seattle as the morning clouds proved too thick to burn off, but other mornings in the future may have little or no clouds at all. Regardless, I predict that over the next two weeks, we will see average temperatures with slightly below-normal precipitation. We've got that big blocking high over the Pacific that will shield us from any storms coming from our west.

 

00z Extended WRF-GFS 36km - 300mb isotachs - 2 A.M. August 6, 2011

Above is a shot of the current winds at the 300mb level of the atmosphere. As you can see, we are stuck in the doldrums between the northern and southern branches of the summer jet stream.

00z Extended WRF-GFS 36km - 3-hour precipitation - 2 A.M. August 6, 2011

The above model shows the predicted precipitation over the previous three hours. There are a few showers to our north, but these will not affect us and are weak anyway. This map confirms that there is a large ridge of high pressure  blocking any systems that come into our area. However, you can see that the center of the ridge is way out at sea (40N, 150W), so it doesn't totally block clouds and precipitation. I still don't expect us to get much rain over the next two weeks though.

00z Extended WRF-GFS 36km - 300mb isotachs - 5 A.M. August 13, 2011

This shows the 300mb winds approximately a week from now. The ridge has broken down some, and the flow is more zonal. However, if you look at the 3-hour precipitation chart from the same time, you will find that no organized systems are anywhere near the Pacific Northwest. The jet stream is still too disorganized to allow any storms to hit the Pacific Northwest. To top it off, the flow still splits around Washington and Oregon, although it is not as clear-cut in this chart as the one before.

00z Extended WRF-GFS 36km - 3-hour precipitation - 5 A.M. August 13, 2011

Even though the details change, the general idea is that Washington will be stranded between two weak jet stream branches and will see typical summer weather. We will have varying levels of cloudiness in the morning, with corresponding burn-off times in the afternoon. No heat waves, no ice ages, and no real precipitation to speak of. Just cloudy mornings, sunny afternoons, and that great natural air conditioning at night.

Thanks for reading,

Charlie

Mirages!

Thursday, August 4, 2011
9:51 P.M.

As I was taking the ferry back from Victoria the other day, I took the picture above. I was seeing a mirage! I had always seen those common road mirages before, where the sun hits the road and it looks like there are black oil slicks ahead of you which fade out as you come near them, but this was completely different. This mirage lasted for hours, and stretched the entire horizon. When I first saw it, I wasn't even on the ferry. I was on the Victoria waterfront. At first, I thought it was a change in water current/color, but as the day went on, it looked more like a fog bank. For some reason though, it looked slightly different. When I got a closer look and saw distorted images like the one above (there is a false image of a boat on top of the boat already there) I knew it was a mirage. And my findings were confirmed when we headed into the "fog bank" only to see the "fog" mysteriously thin out before dying away.

As far as I can remember, this is the first real mirage (besides the ones on roads) that I have seen. It was an incredible sight. Some additional photos are below. They appear chronologically in the order I took them.

 

Inverted boat

  

Fog bank?

 

Looking out from the marina.

 

Another boat. See the two layers?

 

Distorted boat.

 

Taken a few seconds later... boat isn't distorted anymore!

 

Looking back at Vancouver Island

 

It looks a lot like a fog bank, but something is different.

 

Slightly transparent...

The two layers of distortion!!!

As you can see, this mirage was heavily documented by yours truly. I wish I had a better camera! But these are still some great pictures.

I did a little research on mirages. There are two types. Inferior mirages are where the image is below the actual object. Superior mirages are where the image is above the actual object  The pictures below are inferior mirages over the Mojave Desert.

Photographed by Mila Zinkova in Primm, Nevada on April 4, 2007. Released into the public domain.

Road mirage over the Mojave:

Photo credit to scottthezombie. Licensed under Creative Commons Attribution-ShareAlike 3.0

I found a diagram on how a inferior mirage works on the web! Hopefully this clears some things up. 

Photo Credit: Keith C. Heidorn, PhD. aka "The Weather Doctor"

The mirage I saw was a superior mirage. Here is another example of a superior mirage so you have something to compare my pictures to. The picture was taken of Point Reyes National Seashore from San Francisco.

Photo credit: Mila Zinkova. Licensed under Creative Commons Attribution-ShareAlike 3.0

 Here is another diagram from "The Weather Doctor" depicting what happens in a superior mirage.

And finally, here is a diagram from the same guy depicting what I probably saw! You can see the "Haze Zone" in this diagram, which I interpreted as a fog bank. It also says that the mountains appear higher than normal. I didn't notice anything different about the mountains, but I wasn't really paying much attention to them. 

 

Finally, some good websites for extra reading. Both written by "The Weather Doctor!" This guy knows what he is doing.

http://www.islandnet.com/~see/weather/elements/infmrge.htm - inferior mirages

http://www.islandnet.com/~see/weather/elements/supmrge.htm - superior mirages

Whew! That post took me 100 minutes. Hope you enjoyed it!

Charlie

Kelvin-Helmholtz Instability

Tuesday, August 2, 2011
11:01 P.M.

I was recently in Europe touring with my jazz band. Everything was wonderful; the people, the culture, the sights, and the music were all fantastic. However, I also noticed some very interesting weather. While nearly all the trip was hot and sunny, there were some interesting cloud formations that I had the pleasure of seeing while climbing Mt. Vesuvius with my family.

The above picture is one I took while climbing down Mt. Vesuvius. These clouds have "waves" on them that behave in a way similar to waves on the ocean. You could see them breaking and forming over and over again. I'd get out my camera to take a picture, only to see that they were gone by the time I was ready to take one. However, I'd wait a minute or so, and some more waves would form.

These waves are the result of a phenomenon called Kelvin-Helmholtz instability, which was named after Lord Kelvin and Hermann von Helmholtz. Kelvin-Helmholtz instability occurs when there is either one fluid with velocity shear and density differences within it, or it can occur with two different fluids entirely, with velocity shear occurring between the two fluids. A classic example of Kelvin-Helmholtz instability is wind waves. Air is less dense than water and generally moves faster. When moving air comes in contact with the relatively stagnant water, the instability is manifested in waves moving along the surface of the water. Although it is not as visible, the same thing happens in different levels of air velocity. Faster, less dense air moving on top of slower, more dense air can produce the same Kelvin-Helmholtz waves found in water, and when there is sufficient moisture and clouds form, this interaction can be seen. The picture above is the best example I have witnessed of it, but there are better examples out there with the waves stretching on for miles. Take a look at some of the pictures below!

Kelvin-Helmholtz waves over Monument, Colorado. Photo credit: Terry Robinson

Low-elevation Kelvin-Helmholtz waves

Kelvin-Helmholtz waves over Mt. Shasta. Photo credit: Beverly Shannon (1999)

Kelvin-Helmholtz waves in "Starry Night." Painting credit: Vincent van Gogh

One thing seems to be common here. All of the waves occurred in places with uneven topography. Monument, Colorado, is near the Rockies, and hills/mountains are clearly seen in the other photos. My picture was taken by Mt. Vesuvius, and hills are present even in van Gogh's masterpiece. Mountains create instability, and therefore, Kelvin-Helmholtz clouds.

Below is a cool model of Kelvin-Helmholtz instability. I found it on wikipedia. The copyright gives the permission for anybody to use this file. It looks like "Bdubb12" provided the animation and "raeky converted it from animated .gif to ,avi to ,ogv.  

I hope you enjoyed this blog post! It's 12:02 A.M. and time for me to go to bed.

Thanks for reading,
Charlie

Our Natural Air Conditioning and Marine Push

Monday, August 1st, 2011
3:37 P.M.

Marine Push(up)

When people think of Seattle, they probably think of coffee, bad sports teams, and people with webbed feet. They probably don't think of air conditioning. However, we can get pretty hot in the summer. I remember a couple years back at Sea-Tac when the mercury hit 103 degrees. Why do people not have air conditioning then?

Because mother nature gives it to us for free!

Right now we are in a very typical summer weather pattern, with a big high pressure zone off of our coast blocking systems and occasional onshore flow preventing us from getting too hot by continually flushing out our air with cooler air off of the Pacific. First, fog forms on the coast in the morning as the moist air from the previous night cools off and condenses, as cool air can hold less moisture than warm air. Due to differences in heat capacity, the land heats up faster than the ocean, creating local pressure differences, with higher pressure over the sea and lower pressure over the warmer air on land. This creates a "sea breeze," with air flowing from the ocean to the land, as the atmosphere is always trying to balance itself out. For those of you who have taken physics, this is defined as entropy, and is stated in the Second Law of Thermodynamics. The breeze strengthens throughout the day as the temperature differences increase, and subsides after midnight. Still, there is relatively lower pressure in the rest of Western Washington, so this marine air marches on in, kicking out any any air from the previous day. As the temperature cools off, the moisture condenses to form low stratiform clouds and fog on occasion. As the sun comes back up, the clouds "burn off" due to the warming of the atmosphere and the ability of the air to hold more water vapor. Meanwhile, the sea breeze machine on the coast gets going once more, and the process repeats itself.

If that seems confusing, check this article out: http://www.komonews.com/weather/faq/4306832.html
It explains it in more detail and has diagrams to show you. I didn't want to steal any diagrams off KOMO's page.

I was on the deathly slow internet found on BC Ferries and this was all I could manage in an hour. Maybe I'll write another post tonight at my hotel in Victoria.

Thanks for reading!
Charlie