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Posted by Ray
on 6/23/2008, 7:50 am
72.230.154.40
This past Saturday's forecast wasn't that far off, but Sunday's was a total bust. Why? Hindsight is easy, and sometimes useful. We are all familiar with the concept of "spokes" of energy (= precip) rotating around a synoptic-scale low pressure system. Technically, these are waves of positive vorticity embedded in the main low pressure system, which itself is a wave in the general mid-lattitude circulation around the whole planet (a "Rossby" wave, named after their elucidator, Carl Gustav Rossby). And in between the spokes of positive vorticity are spokes of negative vorticity (= good weather or at least not raining or snowing). So at time zero, if one knows both the rotation and translation rates of the big low (they're always rotating, and usually moving from west to east, although sometimes they stop or even move backwards (retrogress), one can extrapolate forward in time and try to predict when a spoke will hit a given area. Early Saturday morning (21 June), all the models had a spoke of bad weather impacting western NY for the first half of Sunday, and all the local forecasters (including yours truly) said so. Now here's the catch: once in a great while, for reasons way too involved to get into here (I will be glad to elaborate sometime), the pattern of spokes abruptly shifts position ("wave jumping), i.e. dissolves as if by magic and then re-forms with spokes at new angular locations. This also happens sometimes in the standing waves we use to soar in, and can really cause the pilot trouble. And that's what happened on Sunday. The spoke of crappy weather which was supposed to come through Sunday morning actually crossed western NY in the middle of the night, and the negative vorticity (reasonably good weather) following it came in on Sunday. A long shot, and no way in hell to predict it.
Forecasting is always a lose-lose situation for the forecaster. Suppose I put out a pessimistic forecast (as per yesterday) and it turns out to be a decent day. Then I get hell for keeping people away from the airport. On the other hand, if I put out an optimistic forecast, people drive out to Dansville, and it turns sour, you can imagine the comments that would be levied, what with the price of gas nowadays. A good friend of mine from grad school days is the chief meteorologist for the NBC affiliate in Portland Maine. He's had people phone in death threats (Joe just calls the FBI...end of problem). Not quite that bad so far at Dansville, although an ice-pick eyeball-stabbing was recently suggested (not weather related, and of course not serious). Bottom line: when I say something like "it's hard to see us doing much of anything in the air", that's the un-scientific version of "there's an 80-90% probability of IFR". And the rest of the sentence would be : "so there's a 10-20% chance it will be VFR, even good soaring." It's just like poker folks...if you can't stand probability-generated pressue, get away from the table. So far, I've called it exactly like I see it, no spin. Take it or leave it.
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