This exercise asks you to apply what you've learned about numerical weather prediction to the cyclone model and the process of self development discussed in Chapter 13. You will work with 12-hour, 18-hour and 30-hour forecasts from the GFS run at 12 UTC on November 5, 2009. The map background for all the progs focuses on the western North Atlantic Ocean and eastern North America.
a. You are given the 18-hour forecast for 500 mb heights, winds, and absolute vorticity (colors indicate relatively large values of absolute vorticity) from the 12 UTC GFS run on November 5, 2009 (valid at 06 UTC on November 6, 2009). Focus your attention on the prominent trough slated to move off the East Coast of the United States. In light of the corresponding 18-hour forecast for mean sea-level pressure isobars, 850-mb temperatures, and precipitation for the six-hour period ending at 06 UTC on November 6, elaborate on the connection between the 500-mb trough and the relatively deep low-pressure system you observe at the surface. Please use references to specific longitudes and latitudes to describe the position of the low-pressure system with respect to the 500-mb trough.
b. Compare the 12-hour forecast for mean sea-level pressure isobars, 850-mb temperatures, and precipitation for the six-hour period ending at 00 UTC on November 6 to the 18-hour forecast in part (a). Was cyclogenesis predicted to occur during this six-hour period? Please explain your answer.
c. You are given the 18-hour forecast of 850-mb heights, isotherms (thin red and thin blue contours), and winds. What feature do you observe in the 850-mb heights in the immediate vicinity where the GFS predicted surface cyclogenesis to occur? What kind of temperature advection was this feature slated to generate south and west of the low-pressure system (east of the Carolinas)? Please explain your answer.
d. In light of your answer in part (c), what should happen to 500-mb heights with time in this area? Please explain in the context of the process of self development.
e. You are given the 30-hour forecast for 500-mb heights, absolute vorticity, and winds (valid at 18 UTC on November 6). Does this prog support your answer in part (d)? Please explain, comparing specific values from the 18-hour 500-mb forecast to this 30-hour 500-mb forecast.
f. Compare the 30-hour 500-mb forecast to the 30-hour forecast for mean sea-level pressure isobars, 850-mb temperatures, and precipitation for the six-hour period ending at 18 UTC on November 6. In what stage of development was this low-pressure system predicted to be at this time (that is, at 18 UTC on November 6)? Please explain.