Expanding warning times for tornadoes....

[Melissa Jablonski]

Patrick, I have a question. Has the effect of the Great Lakes on storms been considered in this process? They and the The Great Salt Lake affect local weather. I have seen storms that were showing up purple or black on radar fizzle when passing to the South of Lake Michigan. The lake also enhances some storms.

 

[Patrick Marsh]

Melissa,

I'm not familiar with any research that specifically examines the impacts of the Great Lakes on severe convective storms. However, the physical processes that do occur as a result of large bodies of water have been studies. Numerical modellers attempt to replicate the physical processes of the atmosphere in their models. The idea is that if we can begin to model the physical processes correctly, then the larger details will be (mostly) correct.

This doesn't always work out in practice because we can't observe (and then model) the atmosphere at the spatial and temporal scales necessary to begin to understand what is happening. This is where projects such as IHOP (International H2O Project) and VORTEX-2 come in. These projects collect high-resolution (in space and time) observations that allow scientists to learn more about the small details that ultimately make a huge impact in convective weather.

More specifically to the cases you raised with Lake Michigan, water heats and cools more slowly than dry air. This has to do with the specific heat capacity of water versus dry air. (One consequence of this is that dry air heats and cools faster than moist air, which is why you tend to have greater temperature swings underneath a large continental high pressure (dry air) than being on the upstream side of the ridge (where moisture transport tends to occur). Based on this it is highly possible that if the lake is warmer than the surrounding environment, storms may tend to pulse up (intensify) when their inflow originates over the warmer, moister lake rather than over the cooler, drier land. The reverse can be true, cooler waters might lead to a weakening trend. Now this doesn't mean that all storms will behave this way. Thunderstorms, and supercells in particular, are very complex entities. Sometimes the change in strength is simply due to changes in the internal storm structure and has little to do with what is beneath it.

 

[Melissa Jablonski]

Thanks for your helpful explaination.