The Offshore Voyaging Reference Site

4 Great Tips From a Professional Meteorologist

CrayXC40

Some years ago the International Association of Professional Meteorologists issued a memo to their membership with full-face and profile photographs of me together with the warning:

Avoid this man at all costs. He is a weather groupie and once he knows you are a meteorologist you will have no peace.

Poor Frank Singleton missed the memo and therefore we were able to sneak up on him. He did try to escape, but Phyllis, being younger than both of us, was able to run him down for the tackle, enabling me to slip the handcuffs on, and so Frank is now captive here at Attainable Adventure Cruising World Headquarters, where we feed him in exchange for the meteorology knowledge that I’m going to share with you in this article.

But seriously, when Frank wrote to me after the publication of my last weather article with a very kind email saying that I had got it right, I used that contact as a springboard to ask the poor man a huge number of questions.

You can learn more about Frank over at his excellent web site, but the short version is that he is a retired professional meteorologist with decades of experience at the British Met Office and an offshore sailor—a perfect combination for our purposes.

You should also know that Frank is totally his own man who calls them like he sees them without fear or favour. He is even willing to disagree with me…just imagine!

Here are four great tips I derived from Frank’s shared wisdom for ways that we can make more comfortable and safer voyages:


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Dick Stevenson

Hi John,
You have done a nice service introducing Frank to a wider audience. I have been in the Med and northern Europe for a decade now and found Frank’s web site and various writings early on. They were (and remain) a big help to understanding the complex systems that wander these regions and in deciding on a package of data sources that covers the bases without becoming data overload.
My best, Dick Stevenson

richard s (s/v lakota)

g f s and g r i b stand for what please ? recognize the latter as a meteorological term but would like to know what they abbreviate please

richard in tampa bay (soon bound for the antilles for a while)

Philip

Shouldn’t you add that, besides computing power, forecast accuracy depends critically on the quality of data used to initialize the model? (“garbage in, garbage out”) Frank’s note of Feb 26, 2012, in which he points out that a 0.1% error in pressure would result in a significant difference in wind speed in the English Channel, seems to illustrate how important good initial conditions are. In some places, such as high latitudes, surface data may be scarce. Or is satellite data — which ought to cover the globe equally well everywhere — all the models need?

Frank Singleton

Hi John

Data analysis and model initialization are critical to weather prediction. As has been said GIGO rules. Ideally we would have accurate, precise data, all at the same time on a regular 3-D grid with short grid lengths horizontally and vertically.

In reality we have a mix of data with variable accuracies, resolutions and times.

Land stations, ships and tethered buoys measure point specific values at fixed times. Resolutions are nowhere near small enough. Radiosondes make temperature, humidity, wind ascents at fixed times over land with large data gaps especially over the oceans. Drifting buoys provide point specific values but are paged on an as and when basis. Aircraft provide point specific values at various times. Low earth orbiting satellite microwave instruments provide areal temperature and humidity data with horizontal resolutions of around 50 km and at various times. Vertical resolutions are far more coarse than radiosondes and refer to substantial depths of the atmosphere. Infrared sounders measure absorbtion by CO2 through substantial depths of the atmosphere. These are related to temperature. Horizontal resolutions can be down to a few kilometres. Satellites also provide surface wind data using molecular scattering from the sea surface. Sea surface temperatures are measured using IR radiances.

Geostationary satellites provide wind data from cloud or water vapour area movement but not at precise heights.

Initialization of models involves a form of 4-D analysis using all these data coupled with output from the last run of the weather prediction model. One analysis method (4DVar) is a genuine 4-D scheme. An older scheme (3DVar) is what I call pseudo 4-D. It does use all the same data as 4DVar but is not a true 4-D scheme.

All this is a longwinded way of saying that all available data are, in principle, used. There are many mathematical problems that I do not understand. One obvious problem is how to weight data from relatively few “accurate” in situ instruments with a mass of remotely sensed data of low resolution but in their way quite accurate but measuring the atmosphere in very different ways.

Within the constraints of the available computer power, models (or modellers) tend to be ahead of what is possible using the data available. The data analysis schemes lag behind the demands of models and the availability of data. Increasing global model resolution has improved prediction but I have to wonder how much more can be achieved without an, as yet unforeseen, improvement in satellite observing system resolutions.

There is plenty of good science good mathematics and good technology. However, results are and always will be limited by the reality of the complexity and noise in the atmospheric system.

Frank Singleton

John, remember that these are global models. It is not so much a question of how much information there is in northern latitudes but how much there is globally. A truism is that to be able to predict the weather somewhere, you have to know about weather everywhere.

Bruce Senay

John,
Nice job like always. When one of these weather service websites begins to show their predictions with what actually occurred in an easily seen format instead of immediately removing predictions as that hour passes they will likely hook me. Forecasting has come a long way from when a commercial fisherman taught me in early 80’s the best way to evaluate a NOAA forecast was to add it up- 10-15 kt & 3-5 ft would likely be 25 kits & 8 ft seas! Now much more likely to over call as people don’t get as mad when conditions lighter than predicted but sure do when stronger.

Frank Singleton

Bruce, an advantage of using GRIB files via Saildocs, zyGrib, UGrib and the various tablet apps is that you can always compare a forecast with actuality. The data are saved to your computer. ECMWF does make available its forecasts over the past few days. Some years ago I put up a page at http://weather.mailasail.com/Franks-Weather/Grib-Forecast-Examples. This showed some examples. I should find the time to put up some recent examples. I show two in my book, one was a good forecast and one a poor one.

Frrank Singleton

I have been off-air for some while cruising France and struggling with Win 10 so may be a little out of date.

Fiirst, UGrib is no more. The service has terminated. Of course, if you have the viewer it can still be used with .grb files. A plus for the zyGrib viewer – my preferred option – can use both .grb and .grb.bz2.

If you have a tablet, then Weather4D is worth looking at. It can generate an email to Saildocs. The reply can then be used with other apps – eg iNavX. Weather 4D has a useful facility letting superimpose a meteogram on the chart. By moving the point around you can see the meteogram change. See http://weather.mailasail.com/w/uploads/Franks-Weather/weather4dmeteogram.png

Rick Salsman

Good piece John, Frank Singleton has helped guide my thinking a few times and offered some very good suggestions. I agree with your comments and his about the GFS. Through many years of practical experience on board, I have tried several different models depending on where we are located but I can say that the GFS is the most accurate, most of the time! I like his suggestion to watch for divergence in the model over time to potentially identify model trouble. That makes good sense and I will start to watch for that. Frank Singleton was the one to recommend Xygrib to me which displays the data very well. Thanks for the tips.

Robert B

I think you mean zyGrib (www.zygrib.org)

Robert