The forecast funnel

By Chris Bedford – Sailing Weather Service

Chris Bedford is the world’s leading meteorologist for the sport of sailing. Chris currently serves as the meteorologist for American Magic, the New York Yacht Club entry in the 36th America’s Cup. With over thirty years of experience in marine and coastal meteorology, Chris has consulted with thousands of teams in boats as small as 8 feet and as large as 100+. Besides American Magic, Chris has been a part of ten prior America’s Cup Teams (winning 4) and has supported eight Volvo/Whitbread/Ocean Race Teams (also winning 4). Chris is the meteorologist for the Chicago Yacht Club Race to Mackinac and other CYC racing events. Chris just launched the Marine Weather Academy with Peter Isler, providing in-depth training in marine meteorology.

In my last post, I talked about the triad of theory, observation, and modeling as necessary elements of a good forecast. I also suggested that forecasting by looking at bunch of models and trying to select which to believe is a fool’s errand without understanding the meteorology. Today, I’ll conceptualize a forecast process which respects the triad and places model guidance it in its appropriate place in the forecast process.

A good forecast process follows a scientific approach which can be conceptualized by thinking about weather in terms of scale: Globally (or hemispherically) at first, then gradually narrowing your focus down in spatial coverage to continental, regional, then local scales. This approach is known as “The Forecast Funnel”, illustrated in the following figure – starting big picture, then scaling down to continental (synoptic) scale, then finally to what is called mesoscale (which further microscopes from regional to local).

To better understand the weather phenomena that fall within the scales, the following shows a representation for time and space with various weather/climate phenomena. Blue would fall into Planetary/Hemispheric classifications, green would be synoptic, and red would be mesoscale.

From those conceptual illustrations of the forecast process, let’s put some meat on it using a simple flow chart (from the Australian Bureau of Meteorology).

Note where in the forecast flow chart modeling (NWP a.k.a. Numerical Weather Prediction) falls! Pretty far down and even AFTER you have a basic forecast conceptualized.

In terms of time management, the amount of effort you expend at each step of the forecast process is more or less determined by the type of forecast you are producing AND the specific forecast problem of the day. For example, if your problem of the day is the absorption of a tropical cyclone along the Carolinas into a mid-latitude frontal system moving off the US East coast, you will spend more time reviewing the synoptic scale. Alternatively, if your problem is whether or not thunderstorms will become severe/damaging in a particular area, you’ll focus your time on the smaller, mesoscale.

Next time, I’ll run through a live example of this process.

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