Storm Australian Severe Weather Forum
Severe Weather Discussion => General Weather - all topics not current severe weather. => Topic started by: Mike on 17 March 2007, 01:47:36 PM
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I'd like some comments please re steering winds for storm movement. With storms being steering generally by mid level winds ( generally) which level is more dominant, the 700 or 500mb zone?
If the winds at 700 are say for example 9kts from tne NW and the winds at the 500mb zone are say 2kts from the SW - and not much difference between 700 to 500 which would dominate, the SW winds or NW? I know the wind speed may dominate but is that a general rule of thumb within these areas?
On the other side of the scale, if upper winds above 500 are 50+ from the NE and the middle levels are around 20+ at 700 from the SE and below 500 are around 10kts from N , which would dominate?
Mike
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Mike,
Soundings provide sufficient variables of wind speeds with heights. If hodographs can be drawn by hand or automatically with information input into a computer program, they can certainly indicate the anticipated storm motion. Of course, this is the most likely storm motion. High CAPE situations/level of instability and also boundaries can influence storm motion. I have heard that the average winds based on the 500hPa level can bhe taken as a rough estimate of the steerign winds. But really the way I take it is guestimation. I guess experience comes into it but I just look at the typical winds and what the general progression seems to be and then adjust from there.
Regards,
Jimmy Deguara
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Thanks, Jimmy.
Rather difficult to even 'guess' sometimes when the winds are all over the place, but i'll work on the 500mb area for now until i educate some more on Hodo's. As is today's weather here, without looking at the numbers I can tell the storms are moving NW to SE/E - a few storms around on the coast with their anvils backsheared way back from where they are heading - some strong winds above! (Rumbles abound so I'm out to have a gander!)
Tks again.
Mike
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Mike,
Winds in the tropic are erratic to say the least. Given high CAPE environments, the development in the form of boundaries and the downdraft push have an overwhelming effect on the steering and redevelopment of cells. You'll get to know.
Please also note that this is an art that takes years to accomplish! I have observed people make some tremendous errors in the past - misjudging both speed and direction of movement. That can and has lead chasers to busts when they were onto the storm in the first place or basically into a core punch situation. Before they realise, they wonder what went wrong.
Then you have the restrictions based on the road network that acts as a limitign barrier or soemtimes a nightmare in the decision process.
Regards,
Jimmy Deguara
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Yes, Jimmy a fair comment re chasing the buggers. No shortage of roads up here to chase them, but having a 4wd might be applicable on some of the 'tracks', to which i'm not about to do in my sedan!
And I tested your answer in fact. Chased some storms from our north (until the ocean stopped me) but also noticed that even though the majority of the storms were heading SE from the NW across Darwin as the indices proved in the 500/700mb range, there were two large cells coming in from the South to the North and eventually blew out from cold pools - totally in the oposite direction with little or no wind to push them along from what the sounding chart suggested the wind speeds frm that direction indicated!
The Met bureau even mentioned that we'd be getting storms that would be moving very, very slowly over the next few days and they were on the money with the last storms i mentioned!
Plenty of downdraft on observation as fingers developed at the inflow but did not sustain any punch as the precip marched ahead of the storms. But it's all a learning curve and I appreciate the advice your'e giving.
The monsoon comes around every 30-60 days but although we've got a nice NW flow maybe time might run out for it to return. In about 5 weeks time i'll be twiddling my thumbs and chewing my fingernails with boredom!
Mike