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About PyroCu

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  1. PyroCu

    Snow Squall Warning

    The software vendor was only able to support a limited number of NWS offices this year with the initial operational demonstration of the snow squall warnings. Provided everything goes as expected, the snow squall warnings will be expanded to the entire country for winter 2018-19. The experiences of the 7 initial sites this winter will help to refine things moving forward, so that should be a good thing before the national rollout. And yes, in the meantime, WFOs not included this year can continue to use special weather statements to cover snow squalls and their impacts as needed.
  2. PyroCu

    Snow Squall Warning

    The idea is to baseline the snow squall warnings now, and as HazSimp progresses for short-fused products, the snow squall warnings can be folded into whatever form that ultimately takes.
  3. PyroCu

    NNE Winter 2014-2015 Thread Part 2

    Yeah, the 18Z NAM has SBCAPE 100-150 J/kg at 18z Wednesday across central VT, with steep lapse rates to 600mb. Along with strong arctic boundary, isallobaric couplet, frontogenetic forcing, it looks like a high end snow squall threat early afternoon.
  4. PyroCu

    NNE Winter Thread

    The upcoming pattern is looking favorable for arctic waterspout activity on Lake Champlain. It appears conditions will be best with arctic air and light NW-N winds in place early Tuesday morning and again later Wednesday afternoon and early Thursday morning (with the coldest air in place). The best location is typically toward the southern end of the lake (Whallon Bay, between Charlotte, VT and Essex, NY). Convective cloud depths and associated updrafts are stronger with the longer lake fetch, so those factors are maximized in that area with a northerly wind component. These waterspouts are caused by extreme instability over the relatively warm water (42F at Diamond Island as of Sunday, 1/4/15) and vertical stretching with the convective updrafts. While such whirls are relatively weak, they are interesting anomalies and potentially photogenic. Here is a past example: http://www.erh.noaa.gov/btv/events/15Jan2009/images.shtml
  5. Good discussion. Three quick points: (1) Available science papers on the EML: American Meteorological Society (AMS) Journal articles more than 3-years old are open access (i.e., free) and are available at the following URL: http://journals.ametsoc.org/. So, if you wanted to read some of the seminal papers concerning the EML, you can search for elevated mixed layer and get a list of all the relevant papers, read the abstracts, and download the full PDFs if you wish. A good one with regard to Northeast severe weather is Farrell and Carlson (1989), which reviews the 31 May 1985 severe weather outbreak. Here is the link to that one: http://journals.ametsoc.org/doi/abs/10.1175/1520-0493%281989%29117%3C0857%3AEFTROT%3E2.0.CO%3B2. Of course, there is a reference list at the end of each paper, which can lead to further reading. So, that is one way to gain scientific knowledge on different topics in meteorology, including the EML. Of course, there are many people here that can answer questions should they arise, or you can always e-mail the corresponding author to ask questions. (2) Mathematical fluency vs. forecasting: You are correct, there are folks who are mathematically fluent how haven't a clue how to forecast, because they don't really have a feel for it or much experience applying their knowledge in that way. The opposite is also true; there are individuals that have a great feel for the data and good empirical knowledge/"rules of thumb" who are among the best forecasters, yet don't have the theoretical knowledge. This is true of many disciplines, of course. You might have an expert in music theory that can't play, or a Jimi Hendrix who could flat out PLAY but didn't read music. So the point with respect to the EML and cold pool discussion is not attempting to take the thermodynamic theory into a purely qualitative realm, because it gets confusing and isn't necessarily intuitive without analyzing the equations simultaneously, or at least having that foundation to work from. (3) Mathematical vs. conceptual models: The non-mathematical models you speak of are called conceptual models, and remain an integral part of meteorology and form an important basis for how we visualize atmospheric processes. I'm not sure about "military science", but the Bergen School of Meteorology led by Vilhelm Bjerknes developed conceptual models of cold and warm fronts and the Norwegian Cyclone Model, which was done near the time of World War I. The term "front" was taken from the battlefield and applied to the emerging conceptual model being developed to analyze mid-latitude weather systems at that time.
  6. Well, I believe a discussion of potential temperature and related variables can only be useful through a solid understanding of the relevant equations. In my view, there is little to be gained by having a specific discussion about application of theoretical concepts in meteorology without that foundation. There are many good reads on the elevated mixed layer, and interested individuals should start with those scientific papers as published by the American Meteorological Society and elsewhere. It's perfectly okay if there are parts that aren't fully understood. Even experienced meteorologists with multiple degrees may be unfamiliar with certain methods used to achieve some results. That can serve as an opportunity to investigate things further. For a weather enthusiast, just getting a qualitative understanding of the abstract and conclusions can be a helpful and exciting way to expand one's knowledge. I think specific questions are easier to answer if they come directly from the scientific literature or from a specific weather event. As an example, the Banacos and Ekster (2010) paper includes an annotated sounding (their Figure 1) and accompanying discussion that would likely be helpful in answering questions about features shown in the Omaha soundings above, which does include a "textbook" EML. There is a link to that paper here if you are interested: http://www.erh.noaa.gov/btv/research/BanacosEML_waf.pdf .
  7. The word "potential" implies that air would have a particular temperature or density if it were displayed dry adiabatically to a different pressure level. 1000mb is the level typically used as a reference. The point remains that density has to decrease as you go up in the atmosphere. A cold pool aloft simply isn't "heavier" than the air beneath it. Pressure is due to the weight of all the air above a particular point. So, if you are at the ground (say around 1000mb at sea-level), there is more weight of the air above than there would be at 700mb, or 500mb because there is less depth of atmosphere as one goes upward. Another point is that temperature typically decreases as you go upward in the troposphere. A "cold pool" refers to a relative minimum in temperature in a quasi-horizontal sense. Temperature may decrease more rapidly with height with a cold pool (i.e., steeper lapse rates), but temperature still typically deceases on average as you go upward from the surface through the troposphere. So, obviously there is a general state of balance with colder air aloft...otherwise the atmosphere would be "falling down" everywhere! Hydrostatic balance is an excellent assumption. Consider that for synoptic systems (highs and lows, as they might appear on a weather map), vertical motions are typically on the order of cm/s. This is a very small deviation from the vertical force balance, but is still enough to create important weather. Consider that horizontal motions in the atmosphere are typically on the order of 10 ms-1. That is a difference of 3-4 orders of magnitude. Where more appreciable vertical motions exist due to convection (on the order of ms-1), it tends to be over small areas and are a result of strong buoyant forces due to radiative and diabatic processes. A cold pool aloft might cover hundreds of miles. Individual thunderstorm updrafts are much smaller than this. So, we can't really equate strong vertical motion associated with thunderstorms to the larger-scale processes you are interested in. A cold pool aloft arises - in part - from sustained synoptic-scale vertical ascent. We often see them in association with slow-moving low pressure systems aloft. As warm air rises it expands and cools, again, because the pressure is decreasing aloft. This can create a relative minimum in temperature over a certain area and it may persist for days as cut-off lows gradually weaken. You’re asking good questions, but keep in mind that these are topics covered in undergraduate thermodynamic courses for atmospheric science majors, which are rooted in calculus and physics. If explanations seem unsatisfactory, it is because they can be difficult to arrive at intuitively without that type of theoretical background.
  8. Hydrostatic balance is an equilibrium condition. The point being that cold pools or EMLs don't simply fall down because there is a vertical balance of forces (which was the question that had been posed). Hydrostatic balance doesn't describe severe weather, in which there are small-scale departures from this equilibrium state due to buoyancy. With convective motions, you'll see air motions on the order of 1-10 m/s with updrafts and downdrafts.
  9. The atmosphere is a fluid. What "keeps it up there" is hydrostatic balance. This is the vertical balance of forces between gravity - which points down toward the Earth, and the vertically directed pressure gradient force - which points up (from higher pressure near the surface to lower pressure aloft; see the y-axis on the sounding). If a volume of air is relatively heavy or light will be manifest as changes in atmospheric pressure to maintain hydrostatic balance, which is one reason why we analyze pressure on weather maps. Note that moisture does not need to be considered to explain this balance. Note also that a "cold pool" is a relative minimum in temperature as seen on a constant pressure (or constant height) chart. In other words, it's a temperature minimum in a horizontal or quasi-horizontal sense. The temperature through the troposphere typically decreases with height, so a "cold pool" isn't any different in that sense. On the sounding, where the temperature and dewpoint come together are typically levels associated with clouds, since the environment is at/near saturation. So, on the CHH sounding this is the case very near the ground and there is also a moist layer between 750-675mb.
  10. If there is more dense air above less dense air, it will overturn immediately, yes. We measure atmospheric water vapor in terms of grams per kilogram, and it doesn't exceed about 4% per unit volume even in a tropical environment. Whether the "cold pool" aloft is relatively moist or not is not of first order importance to understanding hydrostatic balance.
  11. The equation of state is as follows: Pressure = (density) * (gas constant) * (temperature). So, colder air is more dense, assuming constant pressure. That's the key...pressure is not constant, especially in the vertical. And rocks definitely do not float...if there is less dense air below more dense air, it will overturn immediately. You'll see this condition in very limited circumstances (e.g., above a BBQ grill, a mirage in the desert, over a hood of a car on a hot day, etc.. Since the index of refraction changes when the density profile is inverted, you'll see that wavy appearance in the air immediately above these surfaces. As far as moisture goes, it is generally dealt with by using the virtual temperature, which is used in place of the temperature in the equation of state above. It's a small correction factor...the fundamental principle is still the same. So cold pools aloft, EMLs...the bottom line is that the atmosphere is in hydrostatic balance 99% of the time. Such features are not an exception.
  12. PyroCu

    NNE Winter 2013-14 Part I

    That shallow but constant light north to northwest flow will keep the subfreezing air in place across the Champlain Valley. The 12Z NAM has 1.43" ZR at BTV through 1pm Sunday. This won't end well for trees and powerlines.
  13. PyroCu

    NNE Winter 2013-14 Part I

    Agreed. Upstream radar trends looking more solid. Watertown, NY (KART) with 0.06" liquid this past hour.
  14. PyroCu

    NNE Winter 2013-14 Part I

    SREF and NCEP/WPC freezing rain probabilities can be found at the following URLs: http://www.spc.noaa.gov/exper/sref/sref.php?run=latest&id=SREF_prob_zr_precip_01__ http://www.wpc.ncep.noaa.gov/pwpf/wwd_accum_probs.php?fpd=24&ptype=icez&amt=1&day=1&ftype=probabilities
  15. PyroCu

    NNE Winter 2013-14 Part I

    Snow/sleet forecast for Friday. Then, prospect for significant freezing rain Saturday night through Sunday northern VT/NY.