FLSC Message Board: A brush with Bill

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A brush with Bill

Posted by Ray on 8/22/2009, 6:34 am
69.205.81.50

As far back as last Sunday, and up until Wednesday, all our local forecasters had wall-to-wall sunshine forecast for this weekend. Say what? It's bad enough that the 5-day forecast isn't that great, even under "normal" circumstances". But with a monster like Bill out in the North Atlantic? True, earlier this week Bill was thousands of miles away, but it is equally and chastisingly true that no model can predict where a hurricane will be five days later. If the US and Russia go bonkers and detonate all of their nuclear arsenals, the amount of energy released is about what Bill puts out EVERY DAY.

So now were hearing something like "Bill won't significantly affect our weather this weekend". Say what? True, there won't be a washout, and there won't even be much wind (most of the time), for western NY. But the cirrus shield from this storm is awesome and extends hundreds of miles from it's center, just look at the water vapor satellite imagery

http://www.rap.ucar.edu/weather/satellite/g12.2009234.1015_US_wv.jpg

The effect of a hurricane like Bill is felt at all levels of the atmosphere. Hurricanes have the energy to buck the normal west-to-east progression of synoptic-scale systems, indeed they go against it most of their lives, and only turn out away from the coast and go east when they are dying. Bill is interacting with the approaching cold front, slowing it down and causing relatively crappy weather here. Not wall-to-wall sunshine. When Agnes did that, it rained for a week and Mt.Morris dam damn near overflowed.

For glider geeks: we want boundary layer convection. Not deep (= thunderstorm) convection. We'll probably get some of both. Which day is better, you ask? No way I'll stick my neck out. The precise positioning of the huge swaths of wrap around moisture, coming in from the North Atlantic, are beyond the predictive ability of any current model. Neither the GFS nor NGM, normally pretty good out to 48 hours, can tell you. So, there will be both cloudy and sunny intervals both days. There will be showers at times both days, maybe some thunderstorms too. There won't be much wind (except of course in storms). The ridge won't be working most of the time. So what?? We should go for it both days. There are sure to be some interesting flights...some, VERY interesting.

Homework: you learned in high school earth science class that low-pressure systems and hurricanes (the ultimate low) rotate counter clockwise in the northern hemisphere. If you watch a time-lapse satellite view of a hurricane, you see this. Sometimes, you see the lower-level clouds (e.g. around the eye) doing that, and at the same time, you can see the upper-level cirrus "blow off" shield rotating clockwise! Why?

Ray