Two stretches of French water punish a bad weather call harder than anywhere else I have sailed: the Bay of Biscay, where a depression can turn a 350-mile passage into three days of misery, and the Gulf of Lion, where the mistral and tramontane build a steep sea out of nothing in an afternoon. Both are crossings where a weather-routing app stops being a gadget and becomes the thing you plan the whole trip around. Here is how I use them, which ones earn their fee, and what each costs in 2026.
What weather routing actually does
A routing app takes wind and wave forecasts (GRIB files), your boat's polars (how fast it sails at each wind angle), and a start and finish, then computes the fastest or most comfortable route through the forecast weather. For a Biscay crossing that means it can tell you whether leaving Tuesday gets you across ahead of a front, or whether Thursday means beating into 30 knots on the nose.
It is not a crystal ball. It is only as good as the GRIB it is fed, and forecasts decay fast beyond three or four days. But for a timing decision on a 48-hour passage, it is the best tool there is.
PredictWind: the offshore standard
PredictWind is what most serious offshore cruisers run, and for good reason. It pulls multiple forecast models, runs proper weather routing and departure planning, and its Offshore app is built to work over a low-bandwidth satellite connection, which matters once you are out of mobile range.
The pricing in 2026: the Standard subscription, the popular tier for cruising boats, is about 249 dollars a year, with cheaper Basic and Free tiers and a dearer Professional plan above. That is not cheap, but for a Biscay crossing where the routing genuinely shapes your departure window, plenty of cruisers consider it the best money on the boat. The departure-planning view, which lays out the next several days' worth of possible start times and the passage each would give you, is the feature I use most.
PredictWind earns its keep precisely when you are offshore and out of phone signal. To refresh GRIBs mid-passage across Biscay you need a connection, which for most of us now means either a satellite link or accepting you sail on the forecast you left with. My notes on Starlink on a boat in France cover whether a dish is worth it for exactly this job.
Windy: brilliant value, lighter on routing
Windy is the app I open most for a quick look, because the visualisation is superb and the entry price is almost nothing. Windy Premium runs around 19 to 24 euros a year and unlocks higher-resolution forecasts, ad-free access and the Passage Planner plugin that adds weather routing.
For coastal hops and short passages where I have mobile signal, Windy does almost everything I need at a tenth of PredictWind's cost. Its routing is less sophisticated and it is built around an internet connection rather than satellite GRIB downloads, so for a long offshore leg out of phone range it is weaker. But for a Gulf of Lion crossing that you can time from a marina with good data, it is hard to beat for the money.
Meteo France: the official voice you must not skip
No app, however clever, replaces the official forecast. Meteo France issues the coastal bulletins (the bulletin cotier) and the BMS gale warnings (Bulletin Meteorologique Special) that are the legal and practical backbone of French marine weather. The routing apps model the future, but the BMS is the authority telling you a gale is coming, and the French coastguard broadcasts it.
I treat the official forecast as the veto and the routing app as the planner: if Meteo France has a BMS out for my sea area, no app's optimistic route changes my mind. Getting French marine weather in your own language is its own small skill, and my guide to the France marine weather forecast in English walks through the sources and how to read them.
The Biscay workflow I follow
For a Biscay crossing, here is the sequence that has kept me on the right side of the weather.
Five to seven days out, I start watching PredictWind's departure planner and the model spread, looking for agreement between the forecast models on a clear window. Wide disagreement means low confidence and I hold.
Two to three days out, I narrow to a target departure and cross-check against Meteo France for any BMS in the Biscay sea areas. The official warning trumps the model.
The morning of departure, I download fresh GRIBs and run a final route, then make sure I have offline copies of charts and forecasts because I will lose mobile data 15 to 20 miles out and the rest of the crossing is a connectivity black hole unless I have satellite. Where the signal dies is predictable, and I lay it out in my piece on boat internet in France.
Mid-passage, if I have a connection I refresh the routing daily. If I do not, I sail the forecast I left with and watch the sky and barometer, which is what sailors did before any of this existed.
The Gulf of Lion is a different beast
The Med crossing from the Riviera or Languedoc towards the Balearics or Corsica is shorter but trickier in one way: the mistral and tramontane can build extremely fast and produce a vicious short sea. Here the routing app's value is less about a multi-day strategy and more about catching the precise window between blows.
Windy's high-resolution forecasts are excellent for spotting a mistral building over the Rhone valley, and because Med passages are usually short enough to time from a marina with good signal, the cheaper app often does the job. I still cross-check Meteo France, because the gulf has a reputation for catching people who trusted a single optimistic model.
GRIB files, models and not fooling yourself
A word on the thing that makes or breaks all of this: the GRIB file underneath the pretty interface. A routing app is only as good as the forecast it ingests, and forecasts come from models that disagree, especially three or more days out. The skill is not reading the route the app draws, it is reading the spread between the models.
When PredictWind's models broadly agree on the weather for your window, confidence is high and the route means something. When they fan out into wildly different futures, the app will still draw you a confident line, and that line is close to fiction. I have learned to trust a window only when the models converge, and to sit on the dock when they do not, however tempting the optimistic route looks. Biscay punishes optimism.
Resolution matters too. The high-resolution models (1 kilometre grids on the better apps) capture local effects the global models miss, which is exactly what you need for the mistral funnelling down the Rhone or the acceleration zones around the headlands. For the Med especially, pay for the resolution.
What I would carry, and what I would pay
My honest recommendation depends on how far offshore you go.
For genuine offshore work, Biscay and beyond, out of phone range: PredictWind Standard at around 249 dollars a year, paired with a way to download GRIBs at sea. The routing and departure planning are worth it.
For coastal France and short Med hops with mobile signal: Windy Premium at 19 to 24 euros a year does the bulk of it superbly, and you keep the difference.
Either way, Meteo France is the non-negotiable official layer underneath, and your charts and forecasts must be downloaded offline before you leave. The apps plan the passage; the official forecast decides whether you go; and the sea, in the end, has the final word.
