Saturday, May 8, 2010

Mountain Convection and A Strange Whirlwind



During the past few days we have had marvelous, and sometimes impressive, convection over our mountains (as seen in the picture above from Dale Ireland's webcam). The mornings have started out clear or close to it and then by mid-morning puffy white cumulus clouds formed over the Olympics and Cascades. By early afternoon some have grown into towering cumulus congestus and finally into fully formed cumulonimbus with showers and even some lightning.

Dale Ireland has a wonderful high definition web cam aimed at the western Olympics and here is the daily animation for Friday (http://www.drdale.com/lapse/lapse100507.mov).

Take a look at the visible satellite mixture for Friday morning and then at 5 PM. It is not hard to see the building convection from space (35,000 km above the planet!). The convection on Friday was most intense over the western Cascade slopes and the cool down rush of air from the storms pushed westward towards the lowlands, spawning some modest convection at its leading edge.


So why did we see this convection? Convection is the result of vertical instability of the atmosphere-- under the right conditions, when air given a push upwards, it keeps on going for while. Buoyant plumes of air, warmer than their surroundings, move upwards to 10, 20, or even 30 thousand feet in some locations. The atmosphere was close but not quite unstable throughout the region, but over the mountains the instability could be released.

Why is that?

As mountains are heated by the sun, air moves up their slopes and converges near the mountain crests. The two upward air stream create a strong upward current, which can give air parcel enough of a kick upwards to make the air parcel lift enough to become saturated and for instability to be released (I am skipping the details here, but you get the idea...upward motions on the mountains helps cause cumulus to form).

Anyway, things will calm down tomorrow...a perfect Mother's Day..highs in the mid 60s.

And now the fun part of the blog.

A "whirlwind" hit Genesee Park in Seattle this afternoon destroying a tent at a bicycle swap meet and sending a collection of papers into the sky! King TV was so impressed that is started the 10 PM news with it (here is their coverage at 5 PM: http://www.king5.com/news/local/Whirlwind-blows-through-Seattle-park-93204524.html) However, Jim Guy of KING TV was careful not to call this incident a possible tornado, as some outlets implied.

This was not a tornado. And there were no clouds overhead. Sounds like a big, dust devil type circulation. Strong heating at the surface and cool air aloft helps create strong thermals, especially over a nice open field. Such thermals can develop some spin and considerable speed (I suspect most of you have seen dust devils at some time in your life). Anyway, I believe that is what happened. Not the land spout that some have claimed. Fun, but not dangerous.

PS: Here is a video of a dust devil. Warning! An individual in the video uses" colorful" language at the end.

http://www.youtube.com/watch?v=UNttYX_USyM

9 comments:

Cetern1091 said...

SOL LAUNCHES ANOTHER ATTACK AGAINST THE PACIFIC NORTHWEST

Charges are pending for yet another surprise invasion by Sol, a resident of outer space, on the Pacific Northwest region of the United States.

Sol, also known commonly as the sun, began its attack slowly Thursday afternoon before storming the region in full force all day Friday and Saturday. Its blitzkrieg continues this morning, with no slowing in sight. Defenses on the Earth's surface are in extreme deficiency, leaving residents powerless to fight the onslaught.

Plans to charge Sol with aggravated assault are hindered by the sheer size and power of the defendant. Past charges abound with Sol, including involuntary manslaughter, assault, aggravated assault, and arson.

"The largest obstacle with Sol is that we haven't found any effective defense against it yet," said Lyle Simmons, a Washington State Supreme Court Justice. "Prisons are not feasible; we have not yet found the ability to create a prison large enough, let alone out of materials able to withstand the extreme heat of Sol, or to be placed in outer space, to contain it. Even so, Sol attacks remotely, and so even a prison would not stop it from destruction."

"Nuclear options are out of the question as well; nothing we have developed even compares to the power of the sun. We need to work together to find a solution. Until then, Sol will remain completely free to continue to wreck havoc around the world."

The Northwest has been plagued by Sol's attacks regularly the past couple years. The region is even more powerless against them than most of the rest of the world, as in the past, the sun has been more apt to invade other areas of the world, even other areas of the country. Those areas have built up some small degree of defense, including air conditioning and the means to create some clouds and thunderstorms to block Sol, even temporarily.

"It seems Sol has begun to figure out a new location to increase its attacks," said Tom Calonis, Washington State Governor. "We were always happy to have to endure the onslaught less than most places, but it seems that is changing."

"Don't blame it on Sol - blame it on El Niño," remarked a representative of Sol, who refers to himself as Satan. "Sol didn't intend to attack the Northwest, but El Niño has left it no choice."

As for the most recent invasion, some say it was not necessarily a surprise. Natalie Trumbell, a meteorologist with the National Weather Service, says it was expected for days, but felt no warning was necessary based on the ongoing nature of the assault.

"It's one of those things where it has happened so much recently that you don't need a warning anymore, you just have to come to expect it," she commented. "We saw this coming for days, you just have to be prepared. Stay inside, with closed windows, blinds and curtains. The power of Sol has much less effect and destruction that way."

Some, however, were oblivious to the entire event. Filcf Sams, self-proclaimed Pacific Northwest weather guru, said he also saw this coming days or even weeks in advance, but "it's just the sun", he proclaimed. "If you're not getting outside to enjoy it, you belong in an insane asylum."

----------------------------------
Disclaimer: All people and quotes in this story are fictional, with the possible exception of the final quote about the insane asylum.

bruce said...

this explanation of dust devils sounds right, i used to see them on my elementary school ground that got hot in the summer.

bruce said...

i love your bog.
which you would cover the Vancouver BC area.

RLL said...

About 6 pm Sat. here in Chehalis we had a smallish cloud move south and leave a little rain in the area, before it moved on and bright sunlight returned. It was dense enough to create some darkness.

Liembo said...

Back when I was in junior high we were driving to a tiny town called Starbuck in Eastern, WA. Starbuck is nestled in the canyons near the Snake river along the Tucannon River.

I distinctly remember seeing 3 or 4 tight, and very tall dust devils spinning atop a nearby ridge for hours. The dust they picked up cycloned up and then gushed out the top, but the dust devils just lingered, barely moving atop the ridge. If I were to rely on 25 year old memories, I'd say the visible part of the dust devil funnels were 200 feet high.

windlover said...

Last summer here in Eatonville I had a "whirlwind" go through my front yard. It was kind of wierd! It hit my front porch and knocked my welcome sign around....stirred up some dust and rustled the shrubs in front of my house.

smokejumper said...

Yeah, we have one of our largest fields plowed, packed, and seeded right now, so its powdery dirt and saw plenty of dust devils.

Great conditions for them today. First, very dry and lots of dust. Lack of any breeze. Strong sun, cold this morning, but very warm by noon. Lots of heat radiation too.

I notice most dust devils occur mid morning. Also what is very interesting about whirls winds is how many there are around you at any given time but you just can't see them because they usually don't carry debris.

We have tall grassy fields too you can always see invisable whildwinds because the grass will sway in a circular pattern.

I once read the native tribes use to chase dust devils with spears and knives because they believed they contained evil spirits, you ever heard anything about that?

Brian said...

I was hiking over by Leavenworth on Saturday and there were clouds aloft over the mountains to the west and south and rain visible to the south of us. Finally a dark cloud appeared to the west of where we were and when it reached us it precipitated in the form of somewhere between snow and hail (snail?)

Joel said...

I recently caught a dust devil from the air, on approach to Las Vegas McCarran International:
http://www.youtube.com/watch?v=TJHXHa1wLC4

It was also a great weekend to fly handlaunch r/c sailplanes -- lots of lift close to the ground!