WIND
FORECAST MODELS |
Routing computations are only as good as
the wind forecast used as input. Local Knowledge "LK" provides a "wind
model" facility that allows you to create editable wind prediction models by four
different techniques:
 | Convert a standard grib file to editable format |
| Build a model from scratch on a grid of definition points |
| Build a local model with your own choice of definition
points |
| Copy a wind image to create a digital wind file for
routing |
Once in editable format, LK provides a full set of
"point & click" editing tools to modify a wind model, either overall, in
selected locations, or point to point. You can also change the timing and insert
intermediate time points to better reflect what you think will happen. |
| The image below shows a
"grid" type wind model, with wind vector definitions on a grid of points. The
routing program interpolates between definition points, so you can obtain better
resolution by specifying a smaller grid interval between points. You can create such a
model from scratch by specifying the value at each point, convert a standard grib file or
copy wind predictions from a weather image file. |
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| The image below is a wind
forecast at 15 km separation, about 4x the resolution of most grib files. It is typically
possible to get higher resolution wind predictions as images, but you need a digital file
to do routing computations. LK provides a simple method to convert an image into a digital
file. |
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| You can convert a full grib, or cut
down the lat-lon region to just what you need. |
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| BOTTOM LINE:
YOU CAN USE WIND GRIB FILES FROM ANY SOURCE, OR CREATE YOUR OWN MODELS. ONCE
DEFINED, YOU CAN EDIT MODELS IN A NUMBER OF WAYS TO MATCH CHANGING CONDITIONS. |
| , |
COMPARING
DIFFERENT WIND MODELS |
| You can obtain
wind gribs from a number of free sources, or from custom weather services. Chances are, no
two of them will be identical. LK's "WindMaster" facility enables you to compare
up to 3 different models simultaneously, and to compare their predictions at prior
locations with your measured wind during the race. Pick the best one and use the edit
tools to fine-tune it. The example below shows two forecasts (upper v. lower) for the 2002
Bermuda Race. |
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| The example below shows
measured wind (dark vectors) vs. the predicted wind for the better Bermuda Race wind
forecast. The comparison suggests that the forecast is doing a good job in predicting wind
direction, but that it underestimates windspeed. This can be corrected by scaling up the
wind velocities across the model, a simple one-step edit procedure. |
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| BOTTOM LINE: YOU CAN
IMPROVE THE ACCURACY OF YOUR COURSE ROUTING BY PICKING AND TUNING THE BEST WIND FORECAST. |
|
OTHER
TOOLS FOR TRACKING WIND CHANGES AND VISUALIZING EFFECTS ON ROUTING |
| Force 4 has a track
function to show past positions, which are saved as a file for later recall. In addition
to position, the track shows the measured wind vector at each point so that you can see
wind shifts and note trends in context with location. This is also useful in a
windward-leeward course where you will repeat the same leg, helping to forecast wind
variations that correspond to local topography. |
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| Force 4 also has an option
to display the routing solution in terms of the wind predicted at each intermediate point.
The solution below (part of the 2003 Transpac) shows the predicted boat position as a
black dot on each of the comparison routes, and the wind vector predicted by the wind grib
at that location and time. This enables you to get a better idea as to how the solution is
being driven by the different winds anticipated along each route, and where the solution
may be sensitive to features such as regions of very low wind ("holes"). |
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| BOTTOM LINE: LK HAS
UNIQUE WAYS TO BETTER UNDERSTAND WIND AND INFORM TACTICS |
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