an analysis of gust front activity on 14 june 2006 chris bonanno florida institute of technology n.
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An Analysis of Gust Front Activity on 14 June 2006 Chris Bonanno Florida Institute of Technology
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  1. An Analysis of Gust Front Activity on 14 June 2006Chris BonannoFlorida Institute of Technology Rain Shaft

  2. Overview • On June 14th, 2006 FIT Marine Field Projects class collected weather observations at Deseret Ranch in eastern Osceola County off of State Road 192. • Data collected from approximately 12:10 to 1:50 LST • Observation site was suitable (i.e., far away from significant structures). • Of particular interest were measurements associated with the passage of a thunderstorm gust front including: pressure, temperature, wind speed, precipitation, and relative humidity.

  3. Why are gust fronts important? • Gust fronts are accompanied by strong and sometimesdamaging winds up to 100 m.p.h. (~ cat. 2 hurricane). • High winds are a hazard to boating, aviation, agriculture, etc. • Gust front is a region of low-level convergence (air coming together) which can act as a trigger mechanism (i.e., generate additional storms). • Can issue relief (cooling) in the presence of heat stress

  4. Gust Front Anatomy • Gust fronts are the leading edge of cold air associated with the downdraft which can often be visualized by presence of “shelf cloud”. • Gust front passage is noted by: 1. initially light winds, followed by 2. sudden increase in wind speed, 3. temperature drop, 4. onset of precipitation

  5. Example of a Shelf Cloud rain-cooled air warm/moist

  6. Other Gust Front Characteristics • “Mesohighs” often accompany gust fronts. Surface high pressure created by the rain-cooled (heavy) pool of air associated with the downdraft. • Though gust front winds can be relatively strong in Florida, they are most commonly found to be of greatest intensity in the mid-western and plains regions of the United States. • One measure of gust front intensity, in part, can be obtained via the wet-bulb temperature. • Wet-bulb temperature essentially indicates how cool the temperature will be at a given level (in this case the surface) associated with the precipitation-induced gust front.

  7. temperature dew point Wet Bulb Temperature Tw: ~ 23 C or 74 F The wet-bulb temperature is the temperature resulting from evaporational cooling at constant pressure. On a sounding, it will always fall between the dew point and temperature lines.

  8. Thunderstorm Development • Combination of surface heating, instability and an approaching surface trough extending SW from TD Alberto.

  9. Radar Imagery • What are reflectivity images? • radar sends out an electromagnetic pulse and then listens for a back-scattered signal. The energy received by the radar is proportional droplet size and number. This energy is converted to reflectivity which is color coded based on intensity.

  10. 9:45 AM

  11. 10:34 AM

  12. 11:23 AM

  13. 12:12 PM

  14. 12:32 PM

  15. 12:37 PM

  16. 12:42 PM

  17. 12:47 PM

  18. 1:01 PM

  19. 1:35 PM

  20. 1:41 PM

  21. 1:45 PM

  22. 1:51 PM

  23. Observed Gust Front Characteristics • temperature (recall wet-bulb) • precipitation versus temperature • humidity • precipitation and humidity • wind speed • precipitation and wind speed • pressure • precipitation and pressure Order of events (non-simultaneous)

  24. Wet-bulb temperature

  25. precipitation

  26. precipitation

  27. precipitation

  28. Mesohigh

  29. Mesohigh precipitation

  30. Conclusions/Issues • wet bulb temperature is a relatively good predictor of actual gust front temperature (lower bound) • surface temperatures dropped on three distinct occasions two of which mark the passage of gust fronts • barometric pressure increased with the gust front (meso-high) • humidity initially decreases (~10%) – cloud cover? • humidity increases with the advent of precipitation • wind speed and precipitation are highly correlated (precipitation drag + evaporative cooling)

  31. Questions?

  32. References • apollo.lsc.vsc.edu/.../chapter15/gustfront.html • www.mnchasers.org/june172002/undergust-tb.html • http://www.usatoday.com/weather/tg/wgfront/wgfront.htm Kathryn Shontz