Steve Dedman
EF1
- Joined
- Feb 11, 2009
- Messages
- 58
Living in Knoxville, we have an interesting geological/geographical situation regarding thunderstorms. Situated in the Tennessee River valley between the Cumberland Plateau and the Great Smoky Mountains of the Appalachians, we are in a bowl between two sources of orographic lift.
In watching the way storms behave over the last decade that I have lived here, I have a question: how does a rapid drop in terrain effect thunderstorms?
Since a rapid rise in altitude is generally conducive to thunderstorm development, is the reverse then true? IOW, will a drop in terrain (and the accompanying loss of isentropic lift) help to weaken thunderstorms?
Here are some observations that have led to this question:
When storms approach Knox from the west or NW, they tend to fall apart or weaken significantly just west of the metro. When they approach from the south they tend to strengthen just north of the metro. The Cumberland Plateau runs from NE to SW about 30 miles west and NW of Knoxville. This would seem to indicate that the loss of orographic lift that makes storms strong as they approach the Plateau is a big inhibitor of continued strong storm capability. Often we see a re-strengthening between Knoxville and the Smokies as the terrain starts moving upward again.
The storms that really seem to be the strongest and most long-lived approach from the SW - straight up the Tennessee River valley; with no source of orographic forcing.
I know that there are many days here that, were I to feel the same humidity and temps in Oklahoma, I'd be buying canned goods for the storm shelter. Then we get little to nothing in the way of strong storms.
What I am thinking is that as the warm moist air crests the plateau, it runs into a situation where there is air of similar properties (hot and sticky) at lower altitudes, negating the lift. The elevation drop from Crossville (atop the plateau) to Knoxville is not enormous - only about 1000 feet over about 40-50 miles. But is that enough for the bottom to drop out from underneath the storms?
For reference, here is a google terrain map of the area:
MAP
Perhaps someone can shed a little more light on this phenomenon?
In watching the way storms behave over the last decade that I have lived here, I have a question: how does a rapid drop in terrain effect thunderstorms?
Since a rapid rise in altitude is generally conducive to thunderstorm development, is the reverse then true? IOW, will a drop in terrain (and the accompanying loss of isentropic lift) help to weaken thunderstorms?
Here are some observations that have led to this question:
When storms approach Knox from the west or NW, they tend to fall apart or weaken significantly just west of the metro. When they approach from the south they tend to strengthen just north of the metro. The Cumberland Plateau runs from NE to SW about 30 miles west and NW of Knoxville. This would seem to indicate that the loss of orographic lift that makes storms strong as they approach the Plateau is a big inhibitor of continued strong storm capability. Often we see a re-strengthening between Knoxville and the Smokies as the terrain starts moving upward again.
The storms that really seem to be the strongest and most long-lived approach from the SW - straight up the Tennessee River valley; with no source of orographic forcing.
I know that there are many days here that, were I to feel the same humidity and temps in Oklahoma, I'd be buying canned goods for the storm shelter. Then we get little to nothing in the way of strong storms.
What I am thinking is that as the warm moist air crests the plateau, it runs into a situation where there is air of similar properties (hot and sticky) at lower altitudes, negating the lift. The elevation drop from Crossville (atop the plateau) to Knoxville is not enormous - only about 1000 feet over about 40-50 miles. But is that enough for the bottom to drop out from underneath the storms?
For reference, here is a google terrain map of the area:
MAP
Perhaps someone can shed a little more light on this phenomenon?
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