Kyle Brittain
EF1
If this thread has been discussed at length elsewhere, feel free to re-direct.
I was reading about this event the other day and it had me wondering:
https://en.wikipedia.org/wiki/1998_Kissimmee_tornado_outbreak
Why do nocturnal tornadoes tend to occur with a greater frequency in Dixie Alley and Florida than elsewhere?
The only theories I could come up with were based on moisture (and maybe surface wind). Once there is a deficit of net incoming radiation, the surface of the Earth cools - causing the air above to cool as well, in a layer that becomes progressively deeper overnight - granted there are clear skies and light winds. This stable layer is thus resistant to lifting, and deep, moist convection becomes elevated. Moreover, the thermodynamic qualities of low level air is thought to play a crucial role in tornadogenesis, where it needs to be buoyant enough to be lifted and stretched (vorticity) from the surface to the cloud base. In the drier climates of the plains, and especially the high plains, nocturnal tornadoes (especially in the overnight and early morning hours, as opposed to late evening) are quite rare indeed.
Having a source of GoM moisture (mT air) readily available, and thus being climatologically more humid, tornadoes in the southeast would already seem to originate from storms with lower LCL heights than elsewhere in North America. At night, the LCLs would lower even more as the boundary layer cools, meaning that low level vorticity wouldn't have to be lifted as far to contribute to tornadogenesis. My guess is that high moisture quantities in the low levels of the troposphere would cause a lot of outgoing longwave radiation to be re-radiated back to Earth's surface, causing it to cool slower and delay the onset of boundary layer decoupling. Low level stratus could also play a similar role, as could mixing from strong low level winds associated with a synoptically energetic background environment.
Anyone else have any ideas?
I was reading about this event the other day and it had me wondering:
https://en.wikipedia.org/wiki/1998_Kissimmee_tornado_outbreak
Why do nocturnal tornadoes tend to occur with a greater frequency in Dixie Alley and Florida than elsewhere?
The only theories I could come up with were based on moisture (and maybe surface wind). Once there is a deficit of net incoming radiation, the surface of the Earth cools - causing the air above to cool as well, in a layer that becomes progressively deeper overnight - granted there are clear skies and light winds. This stable layer is thus resistant to lifting, and deep, moist convection becomes elevated. Moreover, the thermodynamic qualities of low level air is thought to play a crucial role in tornadogenesis, where it needs to be buoyant enough to be lifted and stretched (vorticity) from the surface to the cloud base. In the drier climates of the plains, and especially the high plains, nocturnal tornadoes (especially in the overnight and early morning hours, as opposed to late evening) are quite rare indeed.
Having a source of GoM moisture (mT air) readily available, and thus being climatologically more humid, tornadoes in the southeast would already seem to originate from storms with lower LCL heights than elsewhere in North America. At night, the LCLs would lower even more as the boundary layer cools, meaning that low level vorticity wouldn't have to be lifted as far to contribute to tornadogenesis. My guess is that high moisture quantities in the low levels of the troposphere would cause a lot of outgoing longwave radiation to be re-radiated back to Earth's surface, causing it to cool slower and delay the onset of boundary layer decoupling. Low level stratus could also play a similar role, as could mixing from strong low level winds associated with a synoptically energetic background environment.
Anyone else have any ideas?
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