An informative comparison between early and late season chasing. Click here to see what tour to choose.
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A new article written by David Gold called "The Evolution of Technology in Storm Chasing”. Click here to read this informative article
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Storm Chaser's : Increase your knowledge on how the atmosphere produces supercells and tornadoes. Read Dave Gold's new series called Picture of the week.
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Another excellent source for the beginning storm chasers is Allan Rosenberg's "Selected Internet Recourses for the Beginning Storm Chaser". Click Here to access his site.
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Dave's Thoughts on interpreting numerical models before the chase:
I feel as if some chasers try to read too much into model forecasts. Please don't attempt to glean any information which is below the spatial/temporal resolution of the model itself. Such inferences are pure nonsense and will likely lead you astray in your goal of forecasting severe storms (unless you are lucky). I hope to put a table here which compares the horizontal and vertical resolution of each operational forecast model. A model can resolve no feature which has a wavelength less than twice the grid spacing in a given direction. Hence, no short-range model currently in use can resolve individual convective elements.
I believe that chasers generally fail to place enough emphasis on trying to predict the evolution of the thermodynamic character of the atmosphere when making a convective forecast. A careful analysis of the morning upper air charts with frequent reference to a skew-t chart for "back-of-the-envelope" calculations of pertinent quantities such as wet bulb potential temperature can go a long way toward developing at least some feel for how the vertical structure of the atmosphere is likely to evolve during the course of the day, what further modifications are needed for convection to develop, and how far north the moist boundary layer air must travel before it can convect. This information is, of course, absolutely essential to making a successful "chase forecast".
In general, the utility of the medium-range model products decreases with the weakening and northward migration of the mid-latitude westerlies which occurs from mid-spring into summer. By mid-late spring, synoptic-scale weather disturbances are much less prevalent and thus play a decreasingly dominant role in preconditioning large-scale regions for convection. Instead, one should pay less attention to the large-scale waves and focus more on the mesoscale/convective regime when making forecasts for severe convection. This means that predictability generally decreases as spring progresses.
Finally, the real atmosphere is just too complicated and our observations just too sparse to be able to make accurate forecasts all the time. Thus, chasers must sometimes rely upon experience, as well as application of conceptual models (which may be lacking for many phenomena), to make a forecast they can live with.
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SOME THOUGHTS ON EL NINO!
1.) Each El Nino is different from the last and so are the forced responses to the large-scale atmospheric and ocean interactions. One of the principal responses in the excitement of the so-called Pacific-North American responses (PNA) pattern. This is a dominating recurring pattern of the Northern Hemisphere large-scale flow and occurs with or without El Nino. This pattern has shown decadal-scale variability. That is, there have veen periods of several years in the record of North Pacific surface pressure ( close to a decade-long) during which time the positive phase of PNA (strong western North American ridge and eastern U.S. trough has prevailed.
2.) Slight variations in the PNA pattern can result in tremendous REGIONAL differences in weather. For instance, if the Western North American high pressure ridge, a key component of PNA, is displaced northward then storm systems will be able to come inland from Pacific and go underneath this ridge. The result would be very heavy winter precipitation over the Southern U.S. On the other hand, if this ridge is displaced southward, the Pacific storm systems will be shunted northward into the Gulf of Alaska and the South and West U.S. will be bone-dry.
3.) We don't really have a clue as to how El Nino interacts with other modes of atmospheric variability. This is the key to why we can't really predict with any certainty how any particular El Nino ( including this one) will affect our weather.
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WHY DOES EL NINO HAPPEN?
It seems that the onset of El Nino is closely related to synoptic-scale weather events, specifically westerly wind bursts within the equatorial waveguide. The latitudinal band between about 2.5 degrees latitude north and south is "dynamically active" - that is supportive of significant waves (Kelvin, Yanai, and Rossby waves in case you are interested) which transport momentum and every rapidly out of that region.
In a time-averaged sense, the winds in the tropical Pacific (and Atlantic) Ocean blow in a more-or-less westerly direction (east-to-west). This is the so-called trade wind regime and it is the most persistent flow regime on our planet. However, once in a while storms (e.g., typhoons) will initiate bursts of westerly winds at the surface. This sets off a chain of events ( without going into detail) which results in a near total reversal of the above trade wind regime. This can , but does not always follow, the occurrence of a westerly wind burst.
This cannot be all that is needed for El Nino to start. Westerly wind bursts are simply too ubiquitous. Why doesn't EVERY westerly wind burst produce an El Nino? It would be like saying that a thunderstorm is the only prerequisite for a tornado! And we chasers KNOW better than that! It may very well turn out that El Nino is the ocean-atmosphere response to the interaction of these "synoptic-scale stimuli ( westerly wind anomalies) with some inherent, recurring large-scale instability of the ocean-atmosphere system. Once compelling argument for the existence of such an unstable mode is the fact that General Circulation Models (GCMs) are able to predict El Nino, albeit with limited accuracy. These models are much too coarse in spatial resolution to detect synopitc-scale events. Thus, westerly wind bursts are not presented in the models, which are used to predict El Nino. Furthermore, statistical models which rely on the existence of a detectable signal ( that is, a large-scale pattern in the data) are able to predict El Nino very well.
I believe that as computer power increases and we are thus able to increase in the spatial resolution of the GCMs and /or embed high resolution "limited area models" into the GCMs in a real time mode, we will be able to resolve transient synoptic events which initiate an ENSO and thus improve our prediction of the phenomenon. Enough for now.