TalcottWx Posted January 3, 2011 Share Posted January 3, 2011 We use the term "energy" to describe vorticity. For instance, you might hear us say, "there is a ton of energy digging on the backside of the trough." This means there is a lot of vorticity diving on the backside of the trough. It's easier and usually accepted to say "energy." The snowgrowth thing is a little more complicated, but the powerpoint might help explain some of the concepts. Basically you want the air to rise in a layer that is saturated (or at least 80-90% RH) in a layer that is preferable between -12C to -18C. This is how you get those great dendrites to form, they love the -12C to -18C temp range...this is optimum. What is the vorticity physically? Or just the accepted meteorology definition of it? Link to comment Share on other sites More sharing options...
#NoPoles Posted January 3, 2011 Share Posted January 3, 2011 ok, i think i read in one of Will's recent post he stated the pv was going underneath us and supressing possible storms the end of this week to the south...i wasn't sure if pv=polar vortex, and it could move that far south... yes i know, basic stuff...but it's always something i've wondered about so why was part of the PV parked over northern ME all last winter? Link to comment Share on other sites More sharing options...
weatherwiz Posted January 3, 2011 Share Posted January 3, 2011 What is the vorticity physically? Or just the accepted meteorology definition of it? Vorticity is basically "atmospheric spin". If you're familiar with the term helicity than vorticity is virtually the same thing. It's a measure of the change in wind direction and/or speed with height. Here is a link to where you can learn more about vorticity and such: http://www.theweatherprediction.com/habyhints/56/ Link to comment Share on other sites More sharing options...
CoastalWx Posted January 3, 2011 Share Posted January 3, 2011 What is the vorticity physically? Or just the accepted meteorology definition of it? Vorticity is a measure of spin in the atmosphere, given a certain area. Jeff haby has a nice breakdown here. There are several different ways to get vorticity. Curvature and speed shear are the big two. This vorticity is important because it leads to divergence in the atmosphere. When air diverges in the atmosphere, you are removing mass. This removal of mass is what allows air to rise from the surface. You can see why troughs are areas where we tend to have these vorticity maxima or vortmaxes. Troughs are features where we have both curvature and speed shear from jet streams. http://www.theweatherprediction.com/habyhints/56/ Link to comment Share on other sites More sharing options...
dendrite Posted January 3, 2011 Share Posted January 3, 2011 ok, i think i read in one of Will's recent post he stated the pv was going underneath us and supressing possible storms the end of this week to the south...i wasn't sure if pv=polar vortex, and it could move that far south... yes i know, basic stuff...but it's always something i've wondered about so why why the part of the PV parked over northern ME all last winter? PV is kind of a subjective term that I think gets overused. I don't like calling every ULL in winter a PV, but rather one with true arctic origin. PV can also mean potential vorticity too, but that doesn't get thrown around a lot in here.The blocking was so strong last year that the PV/ULL was almost semi-permanent over N ME and E Can. btw...Happy New Year to you too. I had bad service and couldn't reply to your text. Link to comment Share on other sites More sharing options...
CoastalWx Posted January 3, 2011 Share Posted January 3, 2011 ok, i think i read in one of Will's recent post he stated the pv was going underneath us and supressing possible storms the end of this week to the south...i wasn't sure if pv=polar vortex, and it could move that far south... yes i know, basic stuff...but it's always something i've wondered about so why why the part of the PV parked over northern ME all last winter? I think Will meant that the blocking (the mega retrograding ridge) will help force the ULL or PV underneath sne. I personally like to only refer to a true polar vortex as a PV. Link to comment Share on other sites More sharing options...
CT Rain Posted January 3, 2011 Share Posted January 3, 2011 Hopefully Kevin reads up on this thread. He could probably learn a lot. Link to comment Share on other sites More sharing options...
BillB Posted January 3, 2011 Share Posted January 3, 2011 Oh, I have so many newbie questions. Let me start with the "millibar". When someone posts data from the NAM or GFS they often refer to the 500, 850, 700 or some other mb. Is this a height or a measure of atmospheric pressure? What is the significance? As ORH_wxman noted, millibar (mb) is unit of pressure. So why do meteorologists refer to pressure rather than altitude? It has to do with the concept of geostrophic wind. The geostrophic wind is an estimate of the wind that would occur when pressure gradient and rotation (the Coriolis effect) forces are balanced. In reality, there are other forces also acting on the wind, such as friction. That is why winds on a surface map usually cross the isobars (lines of constant pressure, used to depict High pressure and Low pressure). Meteorologists plot data from above the surface on constant pressure charts, which display the radiosonde observations at the altitudes where certain standard pressure values are observed. The altitude for the appropriate pressure value is also plotted on the chart. Temperature, dewpoint/dewpoint depression, wind speed, etc. are then analyzed. Winds on these charts are assumed to be in geostrophic balance and thus blowing parallel to the contours of constant altitude (normally expressed in meters or Decameters). This convention of constant pressure surfaces is also followed in many of the output charts from the various computer models. Link to comment Share on other sites More sharing options...
TalcottWx Posted January 3, 2011 Share Posted January 3, 2011 Thanks for the vorticity help! Helicity and vorticity being similar really helps me understand on the large scale. Link to comment Share on other sites More sharing options...
Bostonseminole Posted January 3, 2011 Share Posted January 3, 2011 Ok, here is one that is used all the time how to read on the maps ( upper level )and define.. - NA0 + PNA also the whol MJO, sometimes you guys poinit out different phases..and how they are more conductive to storms in the NE.. thanks! Link to comment Share on other sites More sharing options...
#NoPoles Posted January 3, 2011 Share Posted January 3, 2011 PV is kind of a subjective term that I think gets overused. I don't like calling every ULL in winter a PV, but rather one with true arctic origin. PV can also mean potential vorticity too, but that doesn't get thrown around a lot in here. The blocking was so strong last year that the PV/ULL was almost semi-permanent over N ME and E Can. btw...Happy New Year to you too. I had bad service and couldn't reply to your text. Thanks, and thanks! so how far south into the US can the PV drop? (please realize i may not quite use the terms correctly, but i hope you can understand the gist of my question) what takes it's place in canada, high pressure? does that usually mean northern Canada warms up? Link to comment Share on other sites More sharing options...
CT Rain Posted January 3, 2011 Share Posted January 3, 2011 Vorticity is basically "atmospheric spin". If you're familiar with the term helicity than vorticity is virtually the same thing. It's a measure of the change in wind direction and/or speed with height. Here is a link to where you can learn more about vorticity and such: http://www.theweathe...m/habyhints/56/ helicity and vorticity are not the same thing. Vorticity is the curl of the velocity vector at a given location. In synoptic meteorology we are interested in vertical vorticity. Link to comment Share on other sites More sharing options...
CoastalWx Posted January 3, 2011 Share Posted January 3, 2011 helicity and vorticity are not the same thing. Vorticity is the curl of the velocity vector at a given location. In synoptic meteorology we are interested in vertical vorticity. LOL you're gonna cause their head to spin. Link to comment Share on other sites More sharing options...
CT Rain Posted January 3, 2011 Share Posted January 3, 2011 LOL you're gonna cause their head to spin. vorticity! Link to comment Share on other sites More sharing options...
dendrite Posted January 3, 2011 Share Posted January 3, 2011 LOL you're gonna cause their head to spin. Nice pun. Link to comment Share on other sites More sharing options...
Analog96 Posted January 3, 2011 Share Posted January 3, 2011 As ORH_wxman noted, millibar (mb) is unit of pressure. So why do meteorologists refer to pressure rather than altitude? It has to do with the concept of geostrophic wind. The geostrophic wind is an estimate of the wind that would occur when pressure gradient and rotation (the Coriolis effect) forces are balanced. In reality, there are other forces also acting on the wind, such as friction. That is why winds on a surface map usually cross the isobars (lines of constant pressure, used to depict High pressure and Low pressure). Meteorologists plot data from above the surface on constant pressure charts, which display the radiosonde observations at the altitudes where certain standard pressure values are observed. The altitude for the appropriate pressure value is also plotted on the chart. Temperature, dewpoint/dewpoint depression, wind speed, etc. are then analyzed. Winds on these charts are assumed to be in geostrophic balance and thus blowing parallel to the contours of constant altitude (normally expressed in meters or Decameters). This convention of constant pressure surfaces is also followed in many of the output charts from the various computer models. This is true, but meteorologists also use mb instead of altitude, because of the variations in surface elevation. Here in the East coast, we often talk about the 850 mb temps being such and such. In Denver, Colorado, 850 mb is actually UNDER the surface! I know that YOU know this, but I am writing this for some of the people who don't. Link to comment Share on other sites More sharing options...
weatherwiz Posted January 3, 2011 Share Posted January 3, 2011 helicity and vorticity are not the same thing. Vorticity is the curl of the velocity vector at a given location. In synoptic meteorology we are interested in vertical vorticity. Really? I've always understood the two to be somewhat similar..aren't they like interrelated or something? Link to comment Share on other sites More sharing options...
HoarfrostHubb Posted January 3, 2011 Share Posted January 3, 2011 How about tilt? Anyone want to explain that? Negative tilt = good? I dunno... Link to comment Share on other sites More sharing options...
TalcottWx Posted January 3, 2011 Share Posted January 3, 2011 Nice pun. Meh, whatever. All I need to know is that its basically spin in the atmosphere, lol. Link to comment Share on other sites More sharing options...
Analog96 Posted January 3, 2011 Share Posted January 3, 2011 Really? I've always understood the two to be somewhat similar..aren't they like interrelated or something? Helicity is more related to wind shear. Link to comment Share on other sites More sharing options...
TalcottWx Posted January 3, 2011 Share Posted January 3, 2011 How about tilt? Anyone want to explain that? Negative tilt = good? I dunno... Positive tilt = storm out to sea Negative tilt = more room for the storm to sneak up the seaboard Basically from a common man to another common man. If the trough doesn't swing negative it doesn't support the storm coming this far north most of the time. Link to comment Share on other sites More sharing options...
Analog96 Posted January 3, 2011 Share Posted January 3, 2011 Positive tilt = storm out to sea Negative tilt = more room for the storm to sneak up the seaboard Basically from a common man to another common man. If the trough doesn't swing negative it doesn't support the storm coming this far north most of the time. Extreme positive tilt and the storm moves rapidly Eastward. Extreme negative tilt and the storm could get pulled NW and/or move very slowly. Neutral tilt= basically normal, relatively swift-moving SW-NE system. Link to comment Share on other sites More sharing options...
CT Rain Posted January 3, 2011 Share Posted January 3, 2011 Really? I've always understood the two to be somewhat similar..aren't they like interrelated or something? In synoptic meteorology we care about vertical vorticity which is what you'd see on a 500mb map. Horizontal vorticity is related to helicity and is a measure of vertical wind shear. Link to comment Share on other sites More sharing options...
HoarfrostHubb Posted January 3, 2011 Share Posted January 3, 2011 Extreme positive tilt and the storm moves rapidly Eastward. Extreme negative tilt and the storm could get pulled NW and/or move very slowly. Neutral tilt= basically normal, relatively swift-moving SW-NE system. Thanks to both of you, and congrats! Link to comment Share on other sites More sharing options...
Bostonseminole Posted January 3, 2011 Share Posted January 3, 2011 Extreme positive tilt and the storm moves rapidly Eastward. Extreme negative tilt and the storm could get pulled NW and/or move very slowly. Neutral tilt= basically normal, relatively swift-moving SW-NE system. how can you tell that on the h5 charts? I hear people always saying is going negative..or positive, but I can never tell. Link to comment Share on other sites More sharing options...
TalcottWx Posted January 3, 2011 Share Posted January 3, 2011 Helicity is more related to wind shear. What is seems wiz is trying to put together is the relation between helicity and shear is related to vorticity because it is related to spin in the atmosphere... save all the very confusing degree details Link to comment Share on other sites More sharing options...
weatherwiz Posted January 3, 2011 Share Posted January 3, 2011 Helicity is more related to wind shear. In synoptic meteorology we care about vertical vorticity which is what you'd see on a 500mb map. Horizontal vorticity is related to helicity and is a measure of vertical wind shear. I got it now! Thanks. Link to comment Share on other sites More sharing options...
Analog96 Posted January 3, 2011 Share Posted January 3, 2011 What is seems wiz is trying to put together is the relation between helicity and shear is related to vorticity because it is related to spin in the atmosphere... save all the very confusing degree details But it's important to know the difference. If you read a SWODY from the SPC, you'll see mentions of helicity. You'll never see much talk about that in a winter storm disco. Link to comment Share on other sites More sharing options...
Bostonseminole Posted January 3, 2011 Share Posted January 3, 2011 BL or boundary layer is the lowest part of the atmosphere near the earths surface. I forget the mb it goes up to aloft, want to say the BL is between 1000mb and 900/950mb. Its simply important regarding temperatures in most situations like in snowstorms. The lowest level of the atmosphere, usually the surface up to 1,000 feet or less. thanks! I assume during snow storms we want the bl to be below freezing.. or close to it. Link to comment Share on other sites More sharing options...
Analog96 Posted January 3, 2011 Share Posted January 3, 2011 thanks! I assume during snow storms we want the bl to be below freezing.. or close to it. Obviously, although 33-34F MAY be OK, especially if precip is heavy. Link to comment Share on other sites More sharing options...
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