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Old 01-13-2008, 08:57 PM   #1
MAXUM
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Default **THE** official weather question thread.

OK since I'm the one asking all the questions, figure it's time to start an official weather question thread because I don't know about anyone else but I find the weather and more so the forecasting fascinating.

So here goes the first official question. I understand that certain ingredients are necessary for a storm to form. One thing really baffles me though, and that is the how atmospheric pressure works or changes. So typically a storm is centered around an area of low pressure. Why? How come a storm can't form under high pressure conditions? What is the key ingredient which controls fluctuation in pressures?

Oh and before I forget, a big thanks to CanisLupusArctos for all the wonderful answers provided thus far in the nor easter thread, those took some time to put together and I certainly appreciate the lesson and humor :-)
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Old 01-13-2008, 09:54 PM   #2
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Default Low and High Pressure Areas

Maxum,

I do not think I can do as well as CLA has, but to help share the load, I will give your low and high pressure question a shot.

Low Pressure

When there is a core of warm air, it forms a lift in the atmosphere. That lift is creates a slight vacuum at the center, hence a low pressure area. Near the center, the warm air is lifting and cooler air circulates down away from the low center to replace the air that lifted. In the northern hemisphere, this lifting and cool air recovery spins anti-clockwise or counter-clockwise. The more lift, the deeper the low pressure and the more the spin. During this process, the warm air reaches a point where it can no longer hold all it's moisture and as a result, precipitation begins.

High Pressure

The complete opposite of low pressure. With a high pressure area, we have a cold center with sinking air. That sinking air is like air coming from a leaf blower. This air flow applies a higher pressure at the surface. The cold air is dry relative to the air around it. The more this cold air sinks to the surface, the higher the pressure. Because of the dry air, high pressure areas are associated with clear weather.

There are many web sites that give good, free basic weather information. He are a few of them.

http://www.usatoday.com/weather/wlowpres.htm

http://www.bbc.co.uk/weather/feature...pressure.shtml

http://www.stormsurf.com/page2/tutor...erbasics.shtml

Good luck and thanks for asking!

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Old 01-14-2008, 04:43 PM   #3
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Cool stuff, thanks for the links! You explanation makes sense. Along the same lines is the extreme low pressure in the core of a hurricane a result of the storm's overall measured wind speed?
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Old 01-14-2008, 05:17 PM   #4
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Default Chicken and the Egg?

Quote:
Originally Posted by MAXUM View Post
Cool stuff, thanks for the links! You explanation makes sense. Along the same lines is the extreme low pressure in the core of a hurricane a result of the storm's overall measured wind speed?
Although it is somewhat like the chicken and the egg argument, actually the wind is the result of the very low pressure supporting circulation in a hurricane.

A hurricane is a huge low pressure system with a very warm core. The lift in a tropical system is huge as is the outflow at the top of the storm. The rate of lift and height of lift develops a huge circulation as the storm builds. This happens best when there is little or no shear in the atmosphere The winds at the surface are the result of the vertical air movement at the center, the well distributed outflow at the top and the feeders into the core at the bottom.

Hurricanes need something called coriolis force to make them spin. This coriolis effect is strongest from 5 to 15 north of the equator in the summer. Too close to the equator and you do not get the spin. That is also why real hurricanes form mostly in the summer, however, the season seems to be getting longer each year. Global warming?

Here is a great link to a web page that is the best I know for a slightly technical explanation of hurricanes.

http://en.wikipedia.org/wiki/Tropical_cyclone

For those technical folks, NOAA and the TPC have more technical details on their pages.

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Old 01-15-2008, 12:35 PM   #5
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Default High pressure

has sinking air, low pressure generates rising air.
There is a big difference with hurricane formation they are warm core feeding off warm ocean water The lows (storms) we get here are cold core. Confused yet.
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Old 01-15-2008, 02:38 PM   #6
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LOL this is so much fun and I'm going to make myself look like a complete moron by the time you all are done with me, but for all the lurkers out there I hope this is providing some level of entertainment....

OK capewx you did confuse me with the cold versus hot core storm systems, but let me explain why. My disclaimer here is my question is either going to make me look like I'm somewhat smarter than I thought, or dumb as a door nail.

My understanding of tropical systems is they are usually formed out of a tropical wave or if I'm correct a cluster of ordinary thunderstorms which eventually organize into a larger system. Aren't those thunderstorms cold cored? Or is that irrelevant because of the dynamics involved with how they form and fuel themselves... IE warm moist air combined with lots of upward movement? Then again a thunderstorm doesn't always equate to low pressure formation does it? Let me guess thunderstorms play by a different set of rules right?
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Old 01-15-2008, 04:16 PM   #7
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Maxum, Don't worry, you're not looking like an idiot - You're probably doing a lot of "silent people" a favor because weather is not portrayed very accurately in mainstream media (either too dumb or too complicated,) and the way science is often taught usually makes most people afraid to try to learn it. All this, while science, especially meteorology/climatology, are having drastically bigger effects on our world thanks to a combination of weather- and people-related factors.

For anyone else out there who may be afraid of learning weather because they're not "science-minded people", let me confess now that I'm right-brained, picture-oriented, a photographer/writer... My attempt at college meteorology wasn't successful in the mid-90s. The teaching was all numerical and I wanted pictures. In 2000, all that changed (I was most grateful!) Everything became available as pictures. It became all online too, no more need for a NOAA sattellite dish on your roof in order to look at maps that individuals previously didn't have access to (even off-duty meteorologists at home). The picture representation of weather stuff has just kept getting better and better... before you know it, we'll have "Animated Hi-Def Meteorology in 3-D IMAX". Popcorn, anyone?

What's this mean to you right-brained people? Consider it an advantage, if you want to learn meteorology. Traditional meteorology uses equations to describe how things move and interact, but I have found that a picture-driven mind with a mental movie projector often arrives at very similar conclusions once trained to "see" the way weather moves and interacts with the land. I've expressed this to friends who are number-minded meteorologists who said they often wished they could just imagine a weather animation without the help from a graphics program on a screen. Nobody has to be special in order to understand this stuff but rather, find their own individual ways of understanding it.

Now, to the question about Thunderstorms. They are tiny little areas of low pressure. Whenever one passes over my station I always notice a pressure drop followed by a pressure rise. ANY area of rising air is causing the pressure at the ground to lower, because when air takes off and goes somewhere else (up) it leaves a vacancy at the ground. If all the people on the MOUNT go up above decks to look at the lake, the "people pressure" below decks will get a lot lower. Granted, in the atmosphere air can and does spread out after it rises, unlike the people, who are limited to the ship.

Anyway... the point is that thunderstorms are very localized areas of rapidly rising air. The most severe thunderstorms will even develop their own counter-clockwise rotation/circulation. Those things are fierce.

To get rising air like that, we usually need heat to create or combine with an unstable air mass in order to make the thunderhead. This instability of the air is called "Dynamics." When T-storms rely on a combination of heat and dynamics, It would be fair to call these storms "Warm core" because heat is a necessary part of their balanced diet.

HOWEVER.... Like people in anarchy, thunderstorms can play by their own rules. If they don't have heat, they can still rely on dynamics alone-- a situation I'll describe as "Conditions that cause air to rise as though it was hot, even though it's not." Whenever that happens, it's an indication that the weather system is on steroids. Such was the case with "Thundersnow" that so many people saw during the Blizzard of '78.

The ones that produce hurricanes need heat. Hurricanes need a lot of heat, and a lot of open water, in order to develop their classic pinwheel structure. When they move over land, they get ripped apart by friction with the land... and when they move over cold water, they *usually* lose enough of their "tropical genetics" so they have to be reclassified as "Extratropical" instead of "Tropical." The difference is like eastern coyotes vs. western coyotes. Very similar, but if you put them next to each other you'd start to see the differences.
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Old 01-15-2008, 06:34 PM   #8
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LOL - well let me re-phrase, not general run of the mill idiot, just when it comes to weather. Actually it's neat to get a real world explination for some of this stuff, usually that never happens. I'm sure you could easily make all this stuff seem extremely complicated and no dispute it is, but things can be described in simple terms without stressing the abstract. Heck I try to do the same thing when it comes to computers. Like many things these days simple questions can be answered simply, unfortunately there are those out there who insist on using fancy buzz words and acronyms - I swear half the time just to hear themselves "sound smart". Indeed I find that many in the computer industry I run into that are like that do so as a smoke screen becuase they really have no idea what they are talking about. Who invented the acronym anyways? I'd like to have a word with them. Some one with a good grasp of a certain subject matter can easily explain the complex in simple terms to anyone who has reasonable cognative ability. Heck my brother in law is (no kidding) a rocket scientist and he was able to explain to me how he designed some ion drive rocket motor and I actually understood what he was talking about. Just please... don't ask me to build one or reguratate what he said. Otherwise we'd probably end up trying to fly to mars on a glorified weed whacker.

Well you guys have been great to answer my questions, I can't think of any more that come to mind, but when I do I know where to ask!

Thanks!

MAXUM
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Old 01-16-2008, 12:47 PM   #9
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Default Acronyms

Maxum, You bring up another interesting point with acronyms. While there is lots of truth to the fact that scientists seem to love acronyms in order to sound smart (I had professors who were like that... drove everyone NUTS) there are at least couple of fields where abbreviations and acronyms have a history of necessity - emergency medicine and meteorology.

Not surprising, both fields got their modern-day starts in the military, where they got a hefty dose of AM's (Acronyms, Military.)

On the practical side, emergency medicine requires fast communication especially in a busy setting where there are other patients, so every abbreviation and acronym is a time-saver as long as every doctor and nurse knows what they all mean.

Meteorology's practical acronyms come from aviation. When you're in the cockpit flying through a busy TCA (terminal control area), you need to be able to read & write quickly whenever you recieve communication from the ground.

Therefore a lot of weather shorthand is designed for cockpit use... terms like "SVR TSTMS" mean "Severe Thunderstorms" and stuff like that.
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Old 01-16-2008, 05:27 PM   #10
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If I were a pilot - I think the last thing I'd want to hear on the radio is "SVR TSTMS".

Probably the reason why I can't stand acronyms so much is all this instant messaging and text messaging "language" that's emerged as of late which just adds to laundry list I already have to keep track of.

Guess it's what some call progress, I'll stick to my initial assessment of annoying.
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