NAME ___________________________________________________________________

Meteorology 535/835

 

Homework 5: Due at Beginning of Class, October 7, 2011).

 

 

 

 

1. In Section 2.8, why did Doswell specifically NOT generally include cases for major outbreaks of severe weather (except the March 1994 tornado outbreak? (Lexee is released from this question)

 

 

Severe weather outbreaks tend to be associated with "synoptically-evident" patterns. Examples of events that are more subtle are presented because they prove to be more challenging to forecast.

 

 

 

2. What distinguishes the meteorology of the F5 Plainfield, Illinois tornado event from other tornado events? (There are two factors.) (Lexee is released from this question)

 

First, the parent thunderstorm developed in a "northwest flow" regime, meaning that the mid and upper tropospheric flow was northwesterly rather than more typical southwesterly flow that characterizes the bulk of tornado events. Second, the wind shear parameters, such as bulk shear and the environmental helicty were weak, and not within the threshold values norrmally associated with tornado occurrences. (Hint: it was the storm motion).

 

 

 

3. Why would pattern recognition have failed in helping forecasters assess the risk for the Palm Sunday (in March 1994) tornado outbreak? (Lexee is released from this question)

 

The forecast mid and upper tropospheric flow (as well as the flow that verified) did NOT feature a strong mid and upper tropospheric short wave, trough or cyclone.

 

 

 

 

4. In what circumstance could there be a great deal of vertical shear and strong surface winds, yet no helicity?

 

 

When strong surface winds are parallel to the mid and upper tropospheric winds, the vorticity vector and the wind vector are not tangent to one another. All the vorticity would be crosswise so there would be no helicity generated by the environment in this case.

 

 

 

5. In your own words, but retaining accuracy, describe streamwise vorticity.

 

Streamwise vorticity can be visualized as a combination of translation and vorticity, in which the vorticity vector is parallel to the velocity vector. In that case, as the air is translating, it will also be rotating, producing helical flow.