1324:"Weather"

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BlitzGirl
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Re: 1324:"Weather"

Postby BlitzGirl » Fri Jan 31, 2014 11:12 pm UTC

Garnasha wrote:
jpk wrote:If you care, you already know.
That's... actually a worse response to a question than "just f-ing google it". Just as unhelpful, with a good helping of snobbish passive-aggression thrown in, without the justification of getting tired of people asking google-able questions.
That response makes sense, because jpk doesn't want you to google it. jpk wants you to look it up in your dictionary.
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Re: 1324:"Weather"

Postby PinkShinyRose » Fri Jan 31, 2014 11:25 pm UTC

sondre99v wrote:960MB refers to a pressure of 960 millibars

So meteorologists write millibars as megaB (I thought the symbol for bar was bar)? That's even worse than mcg or mcmol, I mean, at least the mc prefix is not an existing prefix the other way than the μ-. </cringe>
ucim wrote:
Pfhorrest wrote:According to your own figures, interpreted correctly, the required adjustments could range anywhere from a mere gigaform all the way up to a petaform.
Is there a bureaucracy anywhere that can handle that kind of paperwork?

Jose

People's Republic of China, I think they have plenty of resources.
jpk wrote:Put more simply: if you were interested in those details before you read the comic, you're still interested, and you've satisfied your curiosity (by assumption, you're not too stupid or lazy to have done so previously). If you weren't interested enough to learn about those details, nothing has happened to change that fact. The only assumptions we can make which change this reasoning are incredibly rude ones and I'm not going to assume them. So, by courtesy, "if you care, you already know".

There's always the OTT, that's unfathomable.

EDIT: Randall seems to have acquired an obsession with the weather lately.

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Re: 1324:"Weather"

Postby rmsgrey » Sat Feb 01, 2014 3:26 am UTC

jpk wrote:Put more simply: if you were interested in those details before you read the comic, you're still interested, and you've satisfied your curiosity (by assumption, you're not too stupid or lazy to have done so previously). If you weren't interested enough to learn about those details, nothing has happened to change that fact. The only assumptions we can make which change this reasoning are incredibly rude ones and I'm not going to assume them. So, by courtesy, "if you care, you already know".


The comic may have made the details sound more interesting to someone - if nothing else, it provides some keywords to let you bypass the initial stages of learning about something - the ones where you're Googling broad terms in order to find out what the narrow terms to Google are.

Also, Randall exposing an interest in something usually means that there is something actually interesting there, which is probably going to be worth following up on.

Also, "interested" is not a pure binary - instead it's a continuum with a threshold effect, and behaviour around the threshold may not match behaviour at the extremes.

Put more simply: If you were nearly interested enough to find out before, this may have pushed you over...

barnacle
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Re: 1324:"Weather"

Postby barnacle » Sat Feb 01, 2014 3:55 am UTC

If you care about what the jet stream is doing (which drives a lot of surface weather), you probably care about the 500mb chart.

Finally, an XKCD that I know what the hell they're talking about :)

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Re: 1324:"Weather"

Postby JustDoug » Sat Feb 01, 2014 4:11 am UTC

jpk wrote:
Garnasha wrote:
Put more simply: if you were interested in those details before you read the comic, you're still interested, and you've satisfied your curiosity (by assumption, you're not too stupid or lazy to have done so previously). If you weren't interested enough to learn about those details, nothing has happened to change that fact. The only assumptions we can make which change this reasoning are incredibly rude ones and I'm not going to assume them. So, by courtesy, "if you care, you already know".


You can't be interested in something if you don't know it exists and I doubt anyone's curiosity is stirred by not hearing something they haven't heard before (no, that's not a grammatical typo).

It was not curiosity about weather that gave rise to the questioning, but the jargon. A casual interest's curiosity is still curiosity, so "if you care, you already know," doesn't play well here.

In Slashdot Automotive Metaphor mode: you can have a great degree of interest in cars without being familiar with the engineering details, but would probably become quite curious about them if conversation concerning them arose.

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Re: 1324:"Weather"

Postby juliancolton » Sat Feb 01, 2014 4:21 am UTC

Surface pressure 960 mb is very low, and implies significant cyclogenesis has occurred. If that cyclogenesis was a result of the jet stream, as implied, we can assume it was more directly caused by a mid or upper-level jet streak, an embedded area of anomalously strong winds within the broader jet stream. It stands to reason, then—by the theory of transverse circulation—that the characters' location was located either on the southwestern flank or northeastern flank of said jet streak, at least in the northern hemisphere, and assuming a relatively meridional geostrophic flow. These regions are where upper-level divergence is maximized; consequently, the low-level convergence forces large-ascension of air and triggers cyclogenesis.

Seriously, though, weather geeks (or weather weenies, as we call them) do have it rough. When you're at a family barbecue and uncle Ned says "shucks, the sun's out, that tornado watch was all for nuttin!", you can never convince anyone that the stronger the daytime heating, the more likely you'll be affected by thunderstorms. Or why that's only true in some, very specific situations.

Weather comics ftw.

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Re: 1324:"Weather"

Postby addams » Sat Feb 01, 2014 4:31 am UTC

Pfhorrest wrote:Around my parts here in SoCal we haven't had anything close to a gig of weather over the past century cumulatively. Unless you count fire as weather, in which case yeah we got plenty of that.

Yes, Pfhorrest; Fire in SoCal is weather.
They don't call it a fire storm for nothing.

The fires have been very manageable the last few years.
2007 was a very bad fire year. Do you remember it?

That one frightened me.
We had a bad year, then the Aussies had a bad year.

I was so worried.
Were we leading the Parade?

Nope. The following year we were OK.
The Aussies were OK that year, too.

I have no idea why a place so very far away would share atmospheric conditions.
I know it seems obvious. But; It's not. Not to me.

They have their own Jet Stream.
They are a whole planet away from the US.

You explain it.
I simply notice this shit.

ech. I make guesses, sometimes.
What else is a person supposed to do
while waiting for the wind to shift or not?
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Re: 1324:"Weather"

Postby 5th Earth » Sat Feb 01, 2014 4:41 am UTC

I live in California and want to send 150mb of weather to a friend in the midwest. That's too big for an email attachment and I'm not about to set up an FTP server just so he can have a little sun. Any suggestions?
It seemed like a good idea at the time.

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Re: 1324:"Weather"

Postby Mikeski » Sat Feb 01, 2014 4:53 am UTC

5th Earth wrote:I live in California and want to send 150mb of weather to a friend in the midwest. That's too big for an email attachment and I'm not about to set up an FTP server just so he can have a little sun. Any suggestions?

Do both you and your friend have fiber-optic internet service? Just unplug your end during the day.

If your midwestern friend wanted to return the favor, he'll have to ship you our weather in a box...

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Re: 1324:"Weather"

Postby addams » Sat Feb 01, 2014 5:11 am UTC

5th Earth wrote:I live in California and want to send 150mb of weather to a friend in the midwest. That's too big for an email attachment and I'm not about to set up an FTP server just so he can have a little sun. Any suggestions?

No. It remains a good question.
I have been working on sending a little water to Texas.

Spoiler:
I think the best way to send water to Texas is for me to write a nice letter to Texas telling them that their request for water has been received and understood.

Next, I send a letter to Texas explaining that we have very little experience moving that much water. Both the amount of water ready for transport and the delivery system are unique and must be produced. We are working diligently on delivery and have a project due date in two years, 2016.

Then watch the weather.
When one of those low pressure systems builds up out in the Gulf,
Send another letter. This letter says, 'We are ready to test the delivery system.'

When it rains cats and dogs in Texas
and those poor Texans are swimming out of Dallas,
We send another letter telling them that it was our pleasure.

I think it is a great idea!
My nation may have lost its sense of humor.

A person dares not take credit for such things, today.
Those Idiots might believe it!

You can send Sunshine to the MidWest the same way.
You may need to explain that the warmth drains out of the sun during transport.
Life is, just, an exchange of electrons; It is up to us to give it meaning.

We are all in The Gutter.
Some of us see The Gutter.
Some of us see The Stars.
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Those that want to Know; Know.
Those that do not Know; Don't tell them.
They do terrible things to people that Tell Them.

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Re: 1324:"Weather"

Postby vortmax » Sat Feb 01, 2014 7:14 pm UTC

PinkShinyRose wrote:
sondre99v wrote:960MB refers to a pressure of 960 millibars

So meteorologists write millibars as megaB


MB isn't common. You usually see mbar or hPa and occasionally mb, but that is an informal usage.

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Re: 1324:"Weather"

Postby vortmax » Sat Feb 01, 2014 7:28 pm UTC

LambdaBeta wrote:I would love a site that explains how to use the GFS to estimate weather for ourselves. Anybody know of any links to a sort of 'Do your own weather forecast" tutorial?


https://www.meted.ucar.edu/training_detail.php

It's somewhat of a dark at and hard to tutorialize. You really need an understanding of the atmosphere first. The site I linked has great learning modules for all things met. I used them in school and with the NWS. They span the entire spectrum from intro level to pro forecaster, including a good one on forecast models.

Another good way to learn is to start reading area forecast discussions from the NWS and trying to follow along looking at model output, which is available from a number of sources (e.g. http://weather.rap.ucar.edu/model/ )

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Re: 1324:"Weather"

Postby orthogon » Sat Feb 01, 2014 7:47 pm UTC

vortmax wrote:
LambdaBeta wrote:I would love a site that explains how to use the GFS to estimate weather for ourselves. Anybody know of any links to a sort of 'Do your own weather forecast" tutorial?

https://www.meted.ucar.edu/training_detail.php
It's somewhat of a dark at and hard to tutorialize. You really need an understanding of the atmosphere first.

I once tried to learn a bit about ionospheric physics in relation to HF radio propagation. At some point it said "<some phenomenon> simply behaves like weather systems in the troposphere". The idea that the entirety of meteorology is merely a prerequisite for understanding a small part of the topic was enough for me to give up immediately.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1324:"Weather"

Postby Snaake » Sat Feb 01, 2014 8:49 pm UTC

PinkShinyRose wrote:
sondre99v wrote:960MB refers to a pressure of 960 millibars

So meteorologists write millibars as megaB (I thought the symbol for bar was bar)? That's even worse than mcg or mcmol, I mean, at least the mc prefix is not an existing prefix the other way than the μ-. </cringe>
...

No, Randall just does his lettering in all caps. mb or preferably mbar would be correct. Sondre99v said that it refers to 960 mbar, not that the MB is the abbreviation for millibars.

Elaborating on the terms in the comic, answering some questions/comments in this thread, some of which were already answered, but still. Left quotes out for a shorter post (and because the forum was flagging my first attempted response, when I still had more quotes, as spam?):
  • Nothing specific to say on the jet stream layer, other than the weather geek apparently thinks it's in a weird state for the time of the year and place in question. I'm assuming he is referring to end-of-January-2014-US.
  • GFS is the Global Forecast System, run by the US National Weather Service. I don't really know much about the GFS myself, more familiar with e.g. the ECMWF mid-range forecasts (3 to 10 days).
  • 18Z refers to 18 UTC. Numerical weather prediction models can be run e.g. 2 (00Z, 12Z) or 4 (the previous + 06Z, 18Z) times a day.
  • Someone guessed that the "18Z" might refer to an 18-mile grid: the GFS may have a grid of that size at the moment (don't know), but that probably will be, and has been, changed to smaller grid squares as available computing power increases, and is not a permanent feature of the model as such. Or at least, it's a less permanent feature than e.g. the daily cycle that the model is produced with.
  • "By Tuesday" could refer to the GFS being an ensemble model: that is to say, the NWS computes many runs of the model from slightly different beginning scenarios, partially as an attempt to obtain probability distributions for the various possible end-states of the weather, partially to account for errors in the original measurements that the model uses as it's initial state, and probably for other reasons that I'm just forgetting at the moment. IIRC the average of the various ensemble runs is usually more accurate than a randomly-chosen single run. And to finally get to the point on how this is relevant, some runs might predict a low of 960 mbar for e.g. Monday evening, some on Monday morning, and some outliers might predict it for Sunday.
  • Verification is (short description, not an expert) the comparison of weather measurements to the predictions made beforehand, to analyze how accurate the predictions/prediction system/model/etc. is.
  • 960 mbars is low, yes, but not crazy/hurricane-low (I think?). The (mid-latitude) low-pressure system currently just North of Ireland has a mean surface level pressure minimum of just under 960 mbar, on both on the GFS and ECMWF maps. By the time these systems hit the European continent, these systems have usually started to weaken, so it would be somewhat more remarkable to have a sub-960 mbar low pressure system on land. The quickest reference I could find for recorded SLP in a hurricane was off wikipedia for Typhoon Tip at 870 mbar.
  • Note also that 960 mbar can also be the average air pressure in some locales, if they are high enough, but not too high; as a quick estimate, a couple/few hundred meters above sea level should do it. Hence the use of the standard, reduced-to-sea-level air pressures in models and measurements. Air pressure falling with height in the atmosphere is probably most familiar to people from mountaineering or aviation contexts, but it applies all the time. ;)

I'm a nearly-graduated meteorology student at university. I did a bit of quick fact-checking for some of the stuff above, but a lot of it is just off the top of my hat, and as such, not necessarily perfectly accurate or complete information.
Last edited by Snaake on Sat Feb 01, 2014 8:57 pm UTC, edited 1 time in total.

Snaake
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Re: 1324:"Weather"

Postby Snaake » Sat Feb 01, 2014 8:55 pm UTC

orthogon wrote:...
I once tried to learn a bit about ionospheric physics in relation to HF radio propagation. At some point it said "<some phenomenon> simply behaves like weather systems in the troposphere". The idea that the entirety of meteorology is merely a prerequisite for understanding a small part of the topic was enough for me to give up immediately.


Well, you probably wouldn't have to know the entirety of meteorology, just the part that is similar, but that's kind of hard if it doesn't even tell you which element of the weather system it behaves similarly to. Other than that, I'm intrigued, since I did some HF radio stuff, morse code etc., a few years back, but never really looked into the ionosphere physics part of it that much back then.

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Re: 1324:"Weather"

Postby locomusic01 » Sat Feb 01, 2014 9:11 pm UTC

vortmax wrote:It's somewhat of a dark at and hard to tutorialize. You really need an understanding of the atmosphere first. The site I linked has great learning modules for all things met. I used them in school and with the NWS. They span the entire spectrum from intro level to pro forecaster, including a good one on forecast models.

Another good way to learn is to start reading area forecast discussions from the NWS and trying to follow along looking at model output, which is available from a number of sources


Good recommendations, MetEd is a great resource. For anyone who may be interested, I compiled a list of learning resources on my blog a few months ago:

Well, it appears I'm not permitted to post links, but you can find it by Googling "stormstalker resources."

There are plenty of resources to get started, but I don't think a "do your own weather forecast" tutorial is really feasible. I suppose it would only take a few minutes to teach someone how to look at a model and interpret, say, surface temp/dew point, surface winds and precip forecasts, but that's not forecasting so much as reading comprehension. Vort's right, any attempt at real forecasting requires a pretty thorough understanding of the atmosphere and the physics involved.

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Re: 1324:"Weather"

Postby locomusic01 » Sat Feb 01, 2014 9:31 pm UTC

Snaake wrote:"By Tuesday" could refer to the GFS being an ensemble model: that is to say, the NWS computes many runs of the model from slightly different beginning scenarios, partially as an attempt to obtain probability distributions for the various possible end-states of the weather, partially to account for errors in the original measurements that the model uses as it's initial state, and probably for other reasons that I'm just forgetting at the moment. IIRC the average of the various ensemble runs is usually more accurate than a randomly-chosen single run. And to finally get to the point on how this is relevant, some runs might predict a low of 960 mbar for e.g. Monday evening, some on Monday morning, and some outliers might predict it for Sunday.

960 mbars is low, yes, but not crazy/hurricane-low (I think?). The (mid-latitude) low-pressure system currently just North of Ireland has a mean surface level pressure minimum of just under 960 mbar, on both on the GFS and ECMWF maps. By the time these systems hit the European continent, these systems have usually started to weaken, so it would be somewhat more remarkable to have a sub-960 mbar low pressure system on land. The quickest reference I could find for recorded SLP in a hurricane was off wikipedia for Typhoon Tip at 870 mbar.

I'm a nearly-graduated meteorology student at university. I did a bit of quick fact-checking for some of the stuff above, but a lot of it is just off the top of my hat, and as such, not necessarily perfectly accurate or complete information.


Your answers were correct. Ensembles are especially useful for a few reasons. The model's equations can't fully encompass all of the processes that are going on in the atmosphere, there are many gaps in which we receive no observational data, the observations themselves aren't precisely accurate, and the models are somewhat limited in resolution. The errors are often quite small, but they can obviously produce large differences over time. Ensembles give us a rough layout of the possibilities. The ensemble mean is useful because it helps to smooth out some of the more extreme anomalies in the various members, and it gives us a baseline from which to compare them individually. It isn't necessarily more accurate though, because sometimes the various members will be clustered into two distinct solutions, and the mean will just blend the two into an average that doesn't necessarily represent what the models are predicting.

As for the 960 mbar low, that'd be quite impressive for a mid-latitude extratropical system. A 960 mbar tropical cyclone would most commonly translate to Category 3 intensity, though the relationship between wind speed and pressure is more complex than that.

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Re: 1324:"Weather"

Postby vortmax » Sat Feb 01, 2014 11:36 pm UTC

I can help a little too (and maybe put my fancy degree to good use)

  • It is very odd to call it the 'jet stream layer'. We pretty much always name specific layers...so we would be talking about the 300mb layer, or just the upper level jet.
  • you are right on the name.
  • 18Z refers to 18 UTC. Yep. The main runs finish at 0Z and 12Z, but mid-cycle runs at 6Z and 18Z are performed as well. Only the 0Z and 12Z runs ingest upper air data from balloon launches, so the 6Z and 18Z runs aren't usually all that great. There are a few other models that are run with different update rates and different resolutions, all of which are compared against one another. Some handle certain situations better than others, and some have known biases. When someone talks about 'good agreement' in the models, it means multiple models are telling the same story, which increases confidence in the solution.
  • The GFS is spectral (it's domain is defined in frequency space), but it translates out to about a 28 km lateral grid out to 16 days. I believe the model is being updated this year to increase resolution.
  • From this convo, the guy appears to be excited about a developing surface low. I took the "by Tuesday" comment to mean that the model is showing it bottoming out at 960 mbar by Tuesday
  • Yep...basically did the model get it right
  • 960 mbars is low enough I would be watching the models and excitingly talking about it, especially for a mid-latitude cyclone..but not "holy crap we are all going to die" low.

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Re: 1324:"Weather"

Postby PinkShinyRose » Sun Feb 02, 2014 12:11 am UTC

vortmax wrote:960 mbars is low enough I would be watching the models and excitingly talking about it, especially for a mid-latitude cyclone..but not "holy crap we are all going to die" low.[/list]

Would you even notice this? I mean: "Gee willikers, we're all going to die low" probably means you'd notice suffocation symptoms (like when climbing high mountains in the Andes or Himalayas), I assume you'd get nowhere near that now. I'm mostly wondering about things like bottles collapsing after being used, mostly emptied and closed during a high pressure front, or shampoo bottles you closed during this time constantly flowing once you open them in a higher pressure front.

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Re: 1324:"Weather"

Postby Kit. » Sun Feb 02, 2014 10:19 am UTC

PinkShinyRose wrote:I'm mostly wondering about things like bottles collapsing after being used, mostly emptied and closed during a high pressure front, or shampoo bottles you closed during this time constantly flowing once you open them in a higher pressure front.

About 50 g/cm2 compared to average sea level pressure, if the bottle walls are rigid.
Or 1/20 of ideal gas volume difference, if they are not.

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Re: 1324:"Weather"

Postby Snaake » Sun Feb 02, 2014 11:46 am UTC

Yea, the jet stream layer isn't all that usual a term. It's fairly clear what it means though, "the height range of 'here be jet streams.'"

Interesting to learn how the GFS production cycle works, and especially useful to know that the 06Z/18Z runs aren't as good. The ECMWF runs are done for 00Z and 12Z, but their main use is for the mid-range forecasts, and AFAIK pretty much all national weather services in Europe then run their own local area models (with an area of e.g. British Isles+surrounding seas, or Scandinavia+Baltic Sea area, or Iberian Peninsula), probably most of them 4 times a day for a time range of a few days (3 or a bit more?), which use the ECMWF model output as input for the LAMs, to tell them what kind of weather is incoming from outside the area the LAM covers. Due to the smaller area and shorter forecast range (in time), the local area models can use more data (all the balloon launches at least) and have a better resolution. And yea, I'd assume most global models are spectral (the one run by the ECMWF is too).

PinkShinyRose wrote:
vortmax wrote:960 mbars is low enough I would be watching the models and excitingly talking about it, especially for a mid-latitude cyclone..but not "holy crap we are all going to die" low.[/list]

Would you even notice this? I mean: "Gee willikers, we're all going to die low" probably means you'd notice suffocation symptoms (like when climbing high mountains in the Andes or Himalayas), I assume you'd get nowhere near that now. I'm mostly wondering about things like bottles collapsing after being used, mostly emptied and closed during a high pressure front, or shampoo bottles you closed during this time constantly flowing once you open them in a higher pressure front.

If the crazy-low air pressure would be a local phenomenon, you'd "all be dying now" due to being in the middle of a hurricane, with air pressures in 800something or low-900s mbar range, or in a tornado, where I found a mention of an EF2 tornado with an air pressure of 688 mbar, with the surrounding area being about 880 mbar, so that's not too bad either. OR if it's not a local thing and thus doesn't cause violent winds and weather due to the pressure differential, you pretty much have to be climbing tall mountains or flying in a non-pressurized cabin. Grabbing some quick and dirty numbers off an emagram (diagram used to display balloon sounding measurements), 1 km of altitude would have an air pressure of about 900 mbar, 3 km would be a bit over 700 mbar (e.g. Quito is at a bit under 2.8 km), 5 km - about 550 mbar (e.g. Mt. Blanc, 4.8 km), and the highest peaks in the Himalayas are in the sub-350 mbar range. From wikipedia, the "death zone" where there isn't enough oxygen to sustain human life "is generally tagged as 8,000 m (26,000 ft) [less than 356 millibars of atmospheric pressure]."

I'd say synoptic-scale (so stuff bigger than tornadoes and hurricanes - although hurricanes are slightly borderline) high/low pressures generally move slowly enough you won't get weirdness with shampoo bottles, because they're not that airtight. Or more probably because the pressure differential isn't big enough. The only times I remember seeing bottles/cans collapsing or deforming outwards were because of constant-volume thermodynamic processes, i.e. an empty 1,5l coke bottle or similar left in a car that had been heated to room temperature, then after said car has been outdoors for the night at -20°C, the bottle will have collapsed inwards some. Not that rare. The opposite of a bottle "bloating" might happen with an air-conditioned car left out in the sun, where it's temperature could easily rise to above 60-70°C for a similar temperature difference. Calculating the pressure differentials involved (assume no air leaks in/out) is left as a homework excercise.

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orthogon
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Re: 1324:"Weather"

Postby orthogon » Sun Feb 02, 2014 3:22 pm UTC

Bottles quite often crumple if you seal them in a plane at cruising altitude, but cabins of commercial airliners are pressurised to only about 760mbar (8000ft) minimum, so that a bottle sealed at altitude could have a pressure difference of 240mbar at sea level.If you seal a bottle at 960mbar, then at 1000mbar the differential pressure will be just 40mbar, a sixth of the aeroplane case. Plastic bottles are essentially pressure vessels and are quite good at dealing with positive gauge pressure, but not necessarily good when the pressure difference is negative. (The bottle won't crumple if it's still basically full, since water is practically incompressible; a tiny change in the volume of the liquid is enough to produce a large change in the pressure inside the bottle. Similarly if the shampoo bottle is full, not much shampoo needs to ooze out to equalise the pressure.)

Now the homework: to get a similar effect from changes in temperature, we can treat air as an ideal gas and note that the absolute pressure is proportional to absolute temperature (for a fixed volume, e.g. a sealed rigid bottle). A 40mbar drop in pressure therefore corresponds to a 4% drop in absolute temperature, or a change of about 12K(=12°C) from room temperature, which could easily occur during a day (and I would expect Coke bottles to be designed to handle a change from over 30°C in the park to nearly 0°C in the fridge). A 240mbar drop would correspond to a change of 70K, which requires the high air temperatures in Snaake's example, where the greenhouse effect is generating higher temperatures in the bottle than in the surrounding air.

Having said all that, I believe that humans are quite sensitive to relatively small changes in atmospheric pressure. I cite in support of this that Far Side comic with the guys sat on the porch forecasting rain on the basis of swelling in different parts of their bodies ("Well, something's coming: there goes my head"). I've become convinced that I have difficulty sleeping during low pressure, but I don't know whether this has any basis in fact or whether it's just become a self-fulfilling prophecy.

On the ionosphere thing: I admit I was exaggerating unfairly, and the original article did give more information. I think it was something like "particles flow along the isobars as in tropospheric weather", but it was quite throwaway and gave the impression that you needed to know all about meteorology before you could start on the ionosphere. But I think the ionosphere has the basic weather-like phenomena caused by differential pressures and temperatures stirred up by Coriolis forces, plus additional effects due to being made up of charged particles moving in the Earth's magnetic field and under the influence of the solar wind.

</Sunday afternoon ramblings>
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1324:"Weather"

Postby locomusic01 » Sun Feb 02, 2014 4:56 pm UTC

Just wanted to add a little more perspective on the low pressure discussion. The record is a little fuzzy because it isn't clear which reports can or cannot be confirmed, but the lowest non-tropical sea level pressure ever recorded in the continental United States likely occurred on October 25, 2010 at Orr, MN, during the "Octobomb" that brought high winds (70+ mph) to a fairly large area and produced a modest tornado outbreak. At one point the pressure dropped more than 24 mbar in less than 24 hours, which is the threshold for bombogenesis. Not unprecedented, but impressive nonetheless. Alaska has had far, far lower recorded pressures, particularly in the Aleutian Islands/Gulf of Alaska.

The 1993 "Storm of the Century," which was one of the most significant weather events in US history, bottomed out at 960 mbar. It produced a very widespread snowstorm, dumping 20-30+ inches over a big portion of the eastern US and even bringing 12+ inches as far south as central Alabama.

There was supposed to be a snowfall map here, but I can't post images. You can do a search if you're interested.

It also produced a very intense derecho, which spawned a localized tornado outbreak in Florida, as well as extremely high wind gusts (90+ mph). Gusts in excess of 100 mph were recorded as far away as Cuba. There was also a storm surge of 8-12 feet along the west coast of Florida, which would be more in line with a moderately intense hurricane. Nearly 20,000 homes were destroyed in Florida, and the storm system is responsible for 318 deaths in all.

The January 1978 blizzard was at or below 960 mbar as well, and held the record for lowest non-tropical pressure for some time. Very low pressure alone can't tell you much about the weather conditions, but it's pretty fair to assume it'll be active.

As for the lowest tropical sea level pressure ever recorded in the United States, that'd be the 1935 Labor Day Hurricane. A pressure of 892 mbar was recorded at Matecumbe Key when the hurricane made landfall with sustained winds that may have been as high as 200 mph (officially 185 mph). This was the lowest pressure ever recorded in the Western Hemisphere until it was surpassed by Gilbert (1988) and Wilma (2005).

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Re: 1324:"Weather"

Postby thesingingaccountant » Sun Feb 02, 2014 6:03 pm UTC

I think the crux of the joke in this comic is that people use inane comments about the weather as small talk far more frequently than any other subject. Sure, for any given "how 'bout that fill-in-the-blank?" there's at least one expert on it who's going to want to geek out when he hears it, but weather geeks are getting the overwhelming majority of the examples of this phenomenon.

Unless I missed the post, it would seem that I'm the first person to realize this. Not that there's anything wrong with the direction the thread has taken, except that all of the weather jargon is way over my head.
Never trust a psychic who has to reschedule.

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Re: 1324:"Weather"

Postby Snaake » Sun Feb 02, 2014 6:59 pm UTC

thesingingaccountant wrote:I think the crux of the joke in this comic is that people use inane comments about the weather as small talk far more frequently than any other subject. Sure, for any given "how 'bout that fill-in-the-blank?" there's at least one expert on it who's going to want to geek out when he hears it, but weather geeks are getting the overwhelming majority of the examples of this phenomenon.

Unless I missed the post, it would seem that I'm the first person to realize this. Not that there's anything wrong with the direction the thread has taken, except that all of the weather jargon is way over my head.


Well no, I got it. It's just not what interested me in this thread. Maybe ironically, I don't actually consider myself much of a weather geek in my everyday life (I do self-identify as several other kinds of geek though). I've gone long stretches without paying any attention to weather forecasts beyond what my desktop widget or window tells me what it's like right now. :)

And re: the ionosphere stuff, kinda disappointed it was something as boring as that, although I was under the impression that at least for charged particle, electromagnetic forces would be much more important than pressure or temperature differentials, because the atmosphere is so thin, and the temperatures up in the ionosphere are actually pretty crazy (>1000K). Anyway, I'm fairly sure there are other currents/phenomena that align themselves along isobars besides synoptic-scale weather patterns and probably some classes of ocean currents, too... just can't think of examples at the moment. If you or someone else is interested in the synoptic-scale stuff, check the "Geostophic current" on wikipedia. Nice and concise.

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Re: 1324:"Weather"

Postby Nonnie » Sun Feb 02, 2014 9:56 pm UTC

WOW there are giant underground cities built over 2500 years ago! Apparently there are underground cities all over the world! I wish people talked about that instead of the weather...

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Re: 1324:"Weather"

Postby addams » Mon Feb 03, 2014 5:35 am UTC

Nonnie wrote:WOW there are giant underground cities built over 2500 years ago! Apparently there are underground cities all over the world! I wish people talked about that instead of the weather...

But; The thread title is 'Weather'.
It is a very topical subject.

You belong to the first generation of people
that not only talks about the weather;

Your generation of people is also expected
to Do something about the Weather.

What are you going to Do about the Weather, today?
Spoiler:
There is a long list of recommend behaviors.
From Rain Dances and Prayer
to Buying a Pris and becoming conservative
with common resources.
Life is, just, an exchange of electrons; It is up to us to give it meaning.

We are all in The Gutter.
Some of us see The Gutter.
Some of us see The Stars.
by mr. Oscar Wilde.

Those that want to Know; Know.
Those that do not Know; Don't tell them.
They do terrible things to people that Tell Them.

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Re: 1324:"Weather"

Postby iabervon » Tue Mar 25, 2014 5:30 am UTC

The forecast for March 26th, 2014, as of 934 PM EDT Monday Mar 24 2014, is that, off the coast of Massachusetts, there will be a cold-core storm. Some of their models say that the center pressure will drop to 950mb by Wednesday afternoon. So this comic is totally realistic, and I may need a "The GFS says it'll be 960mb by Tuesday. Think it'll verify?" T-shirt.

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Re: 1324:"Weather"

Postby addams » Tue Mar 25, 2014 6:56 am UTC

That's Impressive.

Is it one of These?
http://en.wikipedia.org/wiki/Nor'easter
Those make interesting Tall Tails.

Or; Is it one of These?
http://en.wikipedia.org/wiki/Extratropical_cyclone
Life is, just, an exchange of electrons; It is up to us to give it meaning.

We are all in The Gutter.
Some of us see The Gutter.
Some of us see The Stars.
by mr. Oscar Wilde.

Those that want to Know; Know.
Those that do not Know; Don't tell them.
They do terrible things to people that Tell Them.

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Re: 1324:"Weather"

Postby Snaake » Tue Mar 25, 2014 10:29 am UTC

If it's actually a Nor'easter, it's both. If you read the Nor'easter article, you'll notice a subsection titled "Difference from other extratropical storms" that starts with "A nor'easter is formed in a strong extratropical cyclone..." Btw, there's also an article on cold-core lows in "see also".

The English word "storm" here causes some unnecessary ambiguity, I think. On one hand, it technically applies to any severe weather, but it's also sometimes used for some cyclonic systems that cause stormy weather, in addition to being used for just the weather itself and non-cyclonic phenomena such as hurricanes.

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Re: 1324:"Weather"

Postby addams » Wed Mar 26, 2014 4:46 am UTC

How low did it go?
Do you know?

How low did the Barometer go?
Did it Verify?

Cold Core?
The Storm the book Perfect Storm was about was one of those. right?
http://en.wikipedia.org/wiki/The_Perfect_Storm_(book)

I have never heard the term Cold Core, before.
I bet there is a real good reason they use those words.
Life is, just, an exchange of electrons; It is up to us to give it meaning.

We are all in The Gutter.
Some of us see The Gutter.
Some of us see The Stars.
by mr. Oscar Wilde.

Those that want to Know; Know.
Those that do not Know; Don't tell them.
They do terrible things to people that Tell Them.

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Re: 1324:"Weather"

Postby Snaake » Wed Mar 26, 2014 9:17 am UTC

(to everyone, or noone in particular:) Is addams a spammer, or is his style of writing just... peculiar?
Well, regardless of that (for now):

I don't know how low it has gone, you should be able to look it up yourself.
If it hasn't dropped to 950 mbar yet, you'll have to wait until wednesday afternoon to see if it verifies (a couple of hours to it here,a couple more for UTC time, a few more over in the US). After Wednesday afternoon, this is effectively the same question as the previous.

If the barometer is accurate and there is a barometer at the center of the cyclone, again, it's effectively the same question.
Same question.

Yes, that's what iabervon wrote. There is a wikipedia article titled "Cold-core low", I suggest you try reading that for more information (disclaimer: as with many otherwikipedia articles in at least mathematics and some natural sciences, it may be slightly over the head of a layperson who wants to read just the one article).
I don't know if that's what the book was about, I haven't read it and am not that familiar with cold-core lows.

I haven't heard it much either, but that's partially due to not discussing synoptic weather phenomena in English much. After all, weather is usually predicted in national weather services, which usually use the local language as the working language. Apparently they're also called upper level lows, which is a much more familiar term.
Yes, it's because it "has an associated pool of cold air residing at high altitude" (paraphrasing the wikipedia article).

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Re: 1324:"Weather"

Postby orthogon » Wed Mar 26, 2014 9:34 am UTC

Snaake wrote:(to everyone, or noone in particular:) Is addams a spammer, or is his style of writing just... peculiar?

addams is an institution and would be a national treasure if xkcd were a nation. (And there is anecdotal evidence that he is in fact a she.) I find it's best to let the words wash over you like poetry, but sometimes you'll find pure gold in there.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1324:"Weather"

Postby Snaake » Wed Mar 26, 2014 10:09 am UTC

I was thinking it might be something like that, due to the posts remaining on the site, the non-spammer-y name, and well, the fact that the posts were still relevant, if a bit odd. I have run into various similar "institution" posters elsewhere, but am relatively new to the xkcd forums, hence the question. Thanks for the explanation.

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Re: 1324:"Weather"

Postby PinkShinyRose » Wed Mar 26, 2014 7:23 pm UTC


Could you please add url tags around that? It gives me a strange alternate 859
Snaake wrote:There is a wikipedia article titled "Cold-core low", I suggest you try reading that for more information (disclaimer: as with many otherwikipedia articles in at least mathematics and some natural sciences, it may be slightly over the head of a layperson who wants to read just the one article).

Is "cyclone with cold air patch at the top" a good summary for the cold-core low? My issue with reading wikipedia is mostly figuring out how to stop reading it, so I'm a little careful about going to deep :P.

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Re: 1324:"Weather"

Postby PM 2Ring » Thu Mar 27, 2014 3:35 am UTC

orthogon wrote:
Snaake wrote:(to everyone, or noone in particular:) Is addams a spammer, or is his style of writing just... peculiar?

addams is an institution and would be a national treasure if xkcd were a nation. (And there is anecdotal evidence that he is in fact a she.) I find it's best to let the words wash over you like poetry, but sometimes you'll find pure gold in there.


Someone tried to start a thread in the linguistics forum on Addams-speak, but the mod locked it. OTOH, the there's a thread dedicated to Devanese...

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Re: 1324:"Weather"

Postby addams » Thu Mar 27, 2014 4:40 am UTC

orthogon wrote:
Snaake wrote:(to everyone, or noone in particular:) Is addams a spammer, or is his style of writing just... peculiar?

addams is an institution and would be a national treasure if xkcd were a nation. (And there is anecdotal evidence that he is in fact a she.) I find it's best to let the words wash over you like poetry, but sometimes you'll find pure gold in there.

Thank you.

Thank you for reading my ramblings and replying, sometimes.

Spoiler:
I suppose I should study barometer readings.
A poster noted, Wikipedia is a good source of Knowledge.

It is difficult to stop, sometimes.
When to stop? Wiki is often written like it is all so important to understand. When to stop?

Self guided study is hard.
well..It's not That hard. Is it?

Like any other study; Define the question.
ech. see? That's is a little difficult.

What do I want to know?
umm. Barometric Pressure Stuff.
oh. sure. that will do it. (sarcasm)

One sentence answer:
Barometric is Atmospheric.
There.

There. I know Barometric Stuff, now.
I still have questions.

I am lazy. I want to sit comfortably by the fire, ask questions and have them answered.
GOOGLE can do that.

But; I have to know stuff to go looking for stuff on Google.
I do know stuff. I, just, don't want to review.

I know a review will take me into the History of the Thermomerter.
I will bog down there. I don't want to bog down there.

How did they do it? Weird-O's.
What in God's name were they Thinking?
They were playing with Murcury like I did; Worse!

(Maybe I write like this because of Heavy Metal Poisoning.)

What do I want to know?
Review on Scales and how that stuff is written.
Sure would be nice to have an Old Pro to show me.

Then, How is it done, Today.
Are we able to get a barometric reading from a satellite?
What would we be measuring? What are we bouncing off of it?

If no bounce, then we need a receiver on the ground.
Do we have that? How do we get those numbers?

Of course, I need to review what the stupid numbers mean.
The scale is weird. All scales are weird.

Cue Cueball and his fourteenth competing standard.

If I am going to learn a new competing standard,
I want to know what kind of guesses those are.

Where do the numbers come from?
We can get temp from a distance. right?
How?

See??
Technology answers some questions and begs others.

No matter how much we know we Can Not know it all.
Infinity Plus One. Always, Plus One.


The Universe is Art Work, maybe.
I see the beauty in it, sometimes.


Musing about cosmology is easier than learning Bars of Atmospheric Pressure.
The numbers are meaningless. They are, just, numbers.

With the knowledge of how to read those numbers comes the excitement of looking at one of Those Maps.
Low pressure systems Suck. The lower they are the harder they Suck.

It seems like the air must be going straight up.
How can that be? Hurricane or Tornado.

Hurricanes Suck.
Tornados Suck, more.

Low pressure is fun from a distance.

High pressure systems are simply nice.
Until they turn into extremists.

A high pressure system can be eerie.
The air gets thick.

ech. I'm Lazy.
I might start out with a scale set up horizontally moving from a Tornado on the left to a Boggy Inversion layer on the right.
Labeling the states of weather in Atmospheric Pressure. That would produce a simple visual.

The other scale can hold Sea Level to K-2.
That might work, too.

Maybe. For a not lazy person.
It's not working for me.

I was told knowing when to stop is a Skill artists learn.
I wonder if I will ever learn it.
Life is, just, an exchange of electrons; It is up to us to give it meaning.

We are all in The Gutter.
Some of us see The Gutter.
Some of us see The Stars.
by mr. Oscar Wilde.

Those that want to Know; Know.
Those that do not Know; Don't tell them.
They do terrible things to people that Tell Them.


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