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Posted by RIZ on 6/23/2008, 3:36 pm, in reply to "Weather Forecasting"
70.101.15.134
Kai Gertsen quotes himself as having no pessimism about weather on soaring days. Every day is a good soaring day, Weather... or not. Just come on down, regardless of what the forecast is. Your faith may make a miracle!
--Previous Message--
: 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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