The PredictWind weather routing is the best way to get your trip's most accurate forecast data. The data size is tiny, which is ideal for Satellite & SSB connections.
The weather routing shows the results from 6 forecasts:
ECMWF (Black) ECMWF is the number one ranked global mode from a national weather agency, with a 9 km resolution globally.
Spire (Orange) Spire is the #1 ranked global model from a private weather company, often outperforming ECMWF in the open ocean, 25 km resolution globally.
UKMO (Yellow) UKMO is the number 2 ranked global model from a National weather service—a highly regarded model with 15 km resolution globally.
PWG (Blue) stands for the PredictWind weather model that uses the NCEP global initial conditions for the model run. The resolution available is 1km/8km/50km globally.
PWE (Red) is the PredictWind weather model that uses the European Center for Medium-Range Weather Forecasts global initial conditions. The resolution available is 1km/8km/50km globally.
GFS (Green) Global Forecast System from NCEP as this is used by most other weather websites/apps - 25 km resolution globally.
The weather routing or departure planning will always use the highest resolution (1km,8km,15km, 25km,50km) and the most accurate GRIB files available. As the weather routing or departure planning is calculated on the PredictWind server, it is not dependent on what GRIB files you have downloaded, making the weather routing file size small, typically 5-9kb. The GRIB files are only used to visualize the routing.
This multiple forecast approach is called 'Ensemble' forecasting, where you can have high confidence if all forecasts are similar. If there is a spread in the forecasts and optimal routes, it shows the uncertainty in the forecast.
Tips for interpreting the results
If you are looking at a 'coastal' route, the PWG/PWE forecasts are 1km (Professional Package) or 8km resolution (Standard Package) and will model the geographic/heating effects. The 9km ECMWF and 15km UKMO will pick up some of these effects but not as accurately.
For short-term decision-making, you should select the forecast that appears to be doing the 'best job' of matching the observations. You can use your boat data and data from the observations page in PredictWind.
In addition, try to understand if there is an apparent reason that the routing is going in a particular direction, i.e. is it due to wind direction or strength? Please watch the animation carefully. The weather routing is not an exact road map to follow, but a general trend, as the timing and placement of the weather pattern is never 100% accurate.
If there is a lot of uncertainty, the routes will be spread out, and it may be best to sail the fastest VMC along the course. But generally, the routes should line up for the first 12-24 hours. You should be updating the route with each new forecast every 12hrs. To check when the forecast updates, please review the FAQ.
The routing algorithm will find the best route based on your polar and the forecast. It looks at ALL the possible paths and selects the best route. However, it is only as good as your polar's forecast and accuracy. The forecast is an average of over 1 hour, but the forecast at the lower resolutions, 8km & 50km, is only output every 3 hours. So, the optimum route does not have the granularity to help with short-term wind shifts and variations in wind speed. So, you must decide how best to use the short-term gains over a 3-hour period. We recommend treating the optimal route as a general guide and fine-tuning it for the exact conditions you experience.
The best route is only as accurate as the forecast and the polar you have set. Please ensure you have correctly set up the polar, and the boat speeds shown in the results match your actual boat speeds.
Wind angles we use to define upwind/reaching/downwind
% time upwind = True Wind Angle is 55 degrees or less.
% time reaching = True Wind Angle is between 55 and 135 degrees.
% time downwind = True Wind Angle is 135 degrees or more.
Roll, Vertical Acceleration & Slamming Incidence
These three graphs and tables are new and only available on the Professional Subscription Upgrade Here. They are crucial safety forecasts, and you must review them before setting out. If you're sailing offshore and still need to upgrade to Professional, this is the reason to do it.
To read more about how to interpret these graphs and tables, please look at this article about Wave Polars.