A World of Weather: Chapter 6 Laboratory Question

Chapter 6

7. During the late afternoon of May 9, 1995, a cluster of powerful thunderstorms spawned several tornadoes over the Upper Midwest. The atmosphere became very unstable in the hours leading up to this outbreak of storms.

  1. In Figure 6.16a you are given estimated temperatures at 500 mb (in °F) at 20Z on May 9. Isopleth all even- numbered temperatures. Shade in all closed isotherms to emphasize the location of the coldest air at this level.
  2. In Figure 6.16b you are given surface station models at 20Z on May 9. Isopleth all temperatures that are multiples-of-ten.
  3. Let's now concentrate on the two indicated locations, Rock Island, IL and Minneapolis, MN. How high would you have to lift a parcel of air at these two locations for saturation to occur (assume that the dew point remains constant during ascent)? Round your answers to the nearest foot.
  4. Suppose the height of the 500-mb surface above these two locations at 20Z on this day is observed to be 18,000 ft. Lift the saturated parcels at these two locations to this altitude and determine their temperatures. Use 3.3°F/1000 ft. as the moist adiabatic lapse rate.
  5. For each location, compare the temperature of the parcel at 18,000 ft. to the temperature of the environment at that level as given on the map of 500-mb temperatures. Will the parcels continue to rise or sink back towards the surface? Would you forecast a thunderstorm at either of these locations? What role did the degree of cloudiness play on this day in determining whether thunderstorms would develop?