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of August 13-15, 2005 Answer to Question 4 |
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4. Still 8:30 pm. Examine some upper-air maps (925mb, 850 mb, 500 mb) from 0000 UTC (7pm).
- The 925 mb level is very near the surface. From what direction are the winds at 925 mb? What appears to be their ultimate source region?
- The 850 mb level about 5,000 ft above sea level. From what direction are the winds at 850 mb? What appears to be their ultimate source region?
- Would you characterize the moisture available to Oklahoma and North Texas as "abundant"?
- From what direction are the 500 mb winds across Oklahoma?
- Are the 500 mb winds strong or weak? (At 500 mb, 50 knots is considered "weak")
- Compare the 500 mb winds with the orientation of the surface front. If the forecasted convection indeed occurs, what direction will it go? How quickly will it propagate?
- Why are these ingredients important on this day?
Answer.
- Winds at 925 mb and at 850 mb are generally from the south, and both are ultimately transporting moisture from the western Gulf of Mexico.
- Together, these suggest that moisture is deep and abundant, which are ingredients in sustaining long-lived heavy precipitation.
- Winds at 500 mb are from the southwest at about 15 mph. This is fairly weak, even for August. Storms that form will probably move slowly.
- The 500 mb direction is aligned along the surface front, which suggests that storms will travel along the front.
- Slow moving storms that travel parallel to a surface boundary can set up a "training echoes" flood scenario, especially if the surface boundary is stationary.
The Bottom Line:
- Deep moisture and light steering currents aligned along a surface boundary are important ingredients in flooding and flash-flooding events.
