Weather Movements and a Flip Chart - SailNet Community
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Weather Movements and a Flip Chart

Can those snapshot views off an analyzed weather map be useful? Remember, the weather is in constant motion and all we did was take a snapshot of it at a given time period. The weather has already moved onward. The analysis has changed. So how does this leave the sailor trying to figure out where his passage will be in the scheme of unfolding weather? Let's look at what those analyzed weather maps are and how we can navigate within and around them.

An analyzed weather map represents all the plotted weather parameters frozen at one moment in time. That's a little overly poetic since, in fact, that analysis may well encompass data that came in up to three hours on either side of its analysis time. But for the big picture, I suppose that's close enough to a frozen moment. The result is called a synoptic chart.

Synoptic means "characterized by or affording a comprehensive view," as in my paperback dictionary. I seem to also remember that in a higher priced dictionary it was maybe Greek or something for like a slice or a snapshot, a frozen instant.

There are four major synoptic periods, or times, when the whole world is out taking weather observations that are incorporated into these map analyses. In order that everybody does this at about the same time, a standardized Greenwich Mean Time (GMT) is used. Greenwich, England, is arbitrarily zero degrees longitude, thus the place where time starts - and, I suppose, ends. (Which I'd assume was based on the idea that England felt she owned the world during the epoch when this stuff was all standardized. And, I'd suspect, still thinks so. Probably would have been more logical to also have this be the dateline, but then it would have been difficult to have had all those European wars, what with no one knowing exactly what day it was. So better to plop it in the middle of the Pacific and out of the way.) But since Greenwich appears to have removed itself from the time business, it's now called Universal Mean Time (UMT), just a semantic variation, since the time still starts at zero degrees longitude. But we call it Z time, or Zed time if you will, to avoid any further confusion. Why Z? I haven't a clue.

The common observation times are 00Z, 06Z, 12Z and 18Z. There are further local breakdowns but internationally, these are the common times for surface observation analyses. Upper-air soundings are expensive so these are not only many fewer in number but typically taken only at the 00Z and 12Z time periods.

The only important thing to remember in all of this is that the weather analysis that you see no longer exists. That was simply what everything looked like at that time. We're so used to seeing the ubiquitous weather map that the common assumption is that it remains as depicted until the next map arrives. You receive the map, plot your position on it and, feeling well informed, go on about your routine.

And, in fact, it's really worse than that. The observation is taken, relayed onward via various global circuits, collected, plotted, analyzed, transmitted and at some point in time, eventually winds up in your hand. While the advent of computer plotting and analysis has remarkably accelerated this process, that map may still be three to six hours old by the time it reaches your hand. So that powerful cold front is three to six hours closer to you than the map you're looking at implies. With typical weather feature speed of movement, that front, storm or tropical cyclone can be as much as 100 to 200 miles closer than you thought. In terms of typical boat speeds, that can be a full day's worth of progress.

Sure, a prog chart, or forecast weather analysis, moves the features for you, so why worry about the problem? Well, here are important considerations.

1. The prog may or may not be right. Due to the advances in computer modeling, these short-range     progs of one to three days do have reasonably good odds of being in the ballpark. But they will be     "smoothed out" so that little feature on the analysis that you may be particularly interested in might,     in fact, gets lost in the process. Besides, they aren't consistently accurate enough to bet your life on     them.

2. For whatever reason, you may or may not get the prog that counts. That is, these are
    computer-driven and transmitted after all. I'm sure it's not necessary to point out that computers     are not infallible. They can crash -- just as you're trying to get out of the way of a tropical cyclone.

My recommendation is kindergarten simple, but very effective. Take every surface analysis you can obtain. Store them in a computer (and know how to do it -- I don't) or -- much simpler and equally effective -- if you have a printed copy, just staple the damn things together and make a flip book out of them. You'll be astounded at how the movement of each weather feature just literally jumps out at you. From this flip-chart approach you'll quickly get a feeling for just how fast and in which direction all these features are moving. Done properly and frequently, this approach will lead to a good grasp of the weather movements that will take you beyond the last available analysis.

I find it equally effective to simply flip the charts back and forth for a period of time, while marking the various things I need to know. Select a lat/long point on the west and east side of the map and align those same points for each subsequent map. Then hammer in a couple of staples. Put your map-time boat position on the appropriate map, along with your projected positions. Then see just how the various features are moving around and, more importantly, AT you.

Satellite looping can be approached the same way. But I think it's important to see the more familiar hand-analyzed features in the same light. The satellite shows the effect of these features, while the subjectively hand-drawn features represent the cause.

Sound too simple? Can't be of any use? Try it for awhile first, then let me know what you think.

Bob Rice is offline  
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