Cruising in Practice :: Weather, Wind and Water Flow
The official French weather website is Meteo France which is very good, with clear information (if you have some basic French).
Weatheronline – is as good as any general forecast site, most of which use the same data and the same interpretive-forecast methods. Or the weather buttons below use Accuweather.
France – Climate Generally
France can be divided into a number of climatic zones (excluding the Pyrenean / Alpine zone) :
1. Northern and north-western France – e.g. Le Havre
|The north and north-west of France is affected by the Atlantic. Consequently, it has a changeable, maritime climate like that of the UK. This area of the country experiences relatively mild winters with very infrequent frost and snow. Rainfall tends to be fairly evenly spread throughout the year. Summers in the north are only a little warmer than those in southern England whilst further down the western coast, summers can be very hot and sunny with an average of 7 or 8 hours of sunshine as compared with only 2 hours in winter months.|
2. North-eastern and central France – e.g. Strasbourg
|The area north-east of an imaginary line running between Lille, Paris and Lyon, experiences a mid-latitude, continental climate. This means winters tend to be cold with frequent snow and frost particularly along the eastern border. Rainfall is even throughout the year but generally annual rainfall totals are low. Thunderstorms are common during the warm summers, especially in the south of the area towards the Jura mountains.|
3. South-western France – e.g. Toulouse
|The south-west enjoys warm summers with long periods of sunshine interspersed with short but heavy showers, occasionally becoming quite violent thunderstorms. It can get very hot here but not unbearably so, and summer temperatures can last well into October and even November. The winters are short, with a good amount of sunshine, but also cold, with temperatures sometimes reaching -15 C or below. The worst affected months are probably mid-December through to January, with February usually being very wet.|
4. The Mediterranean Coast e.g. Marseille
Summers are always very warm and sunny and often extremely hot for long periods at a time. For three months (June-August) this region has very little rain other than the occasional thunderstorm. Winters are also generally mild and sunny although they can get unseasonably cold and windy for a few days due to the northerly Mistral wind. The Mistral can also result in cool spring days.
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Hourly wind reports/forecasts for Valence, River Rhone, (l) WindGuru (r) WindFinder
Water Flow – Levels, Currents and Tides
This information is useful in a number of situations – examples include (a) Timing a voyage up or down the River Seine (catching the tidal flow) (b) Watching the Rhone situation and (c) Checking on the water level or flow for a river traverse (e.g the River Baise/Garonne/Lot).
In addition to the specific Rhone website (see following) there is a national website that provides information from monitoring stations on key French rivers. www.vigicrue.gouv.fr – the link will take you to a national map – click on the region you’re interested in. See below for two examples.
(l) Tide levels at Duclair, R. Seine, last 3 days (r) River levels at Valence, R. Rhone, week.
The Rhone – Wind and River Currents
The Mistral – Rhone Valley Wind Forecasts
The mistral is a strong, cold and usually dry regional wind in France, coming from the north, which accelerates when it passes through the valleys of the Rhone and the Durance Rivers to the coast of the Mediterranean Sea around the Camargue region. It affects the northeast of the plain of Languedoc and Provence to the east of Toulon, where it is felt as a strong west wind. It has a strong influence all along the Mediterranean coast of France, and often causes sudden storms in the Mediterranean between Corsica and the Balearic Islands.
The mistral is usually accompanied by clear and fresh weather, and it plays an important role in creating the climate of Provence. It can reach speeds of more than ninety kilometers an hour, particularly in the Rhone Valley. Its average speed during the day can reach about fifty kilometres an hour, calming noticeably at night. The mistral is a regional wind, which usually blows during the winter and spring, though it occurs in all seasons (July is the expected summer month). It sometimes lasts only one or two days, frequently lasts several days, and sometimes lasts more than a week.
Strong southerly winds can happen, too, travelling up the Rhone valley against the current in a classic wind-against-tide situation and conditions can then expected to be particularly choppy and difficult. Of course, in the reverse situation, the Mistral can not only be unpleasantly strong of itself, it can also exacerbate current flow rates meaning that upstream progress can be impossible and downstream progress very difficult to manage (lack of rudder control) – both would be very unsafe and to be avoided.
Wind Forecast websites along the Rhone Valley
- Lyon – http://www.windfinder.com/forecast/lyon_bron
- Avignon – http://www.windfinder.com/forecast/avignon_aeroport
- Port St Louis – http://www.windfinder.com/forecast/mooring_port_saint_louis
- Southern France – Golfe du Lion – http://www.windfinder.com/forecasts/wind_france_s_akt.htm
The Rhone is infamous for its strong current when the river carries large quantities of water: current speeds up to 10 kilometres per hour (8 knots) are sometimes reached, particularly affecting the stretch below the last lock at Valabrègues (Beaucaire-Tarascon) and in some of the concrete canalised by-pass ‘chute’ sections (for example, immediately below Lyon and in the Defile/Canal de Donzere-Mondragon south of Viviers).
The CNR Rhone Navigation website (see above, is very good, if a little tricky to use (it also forces a browser window re-size, sorry). It does, however, provide information about the latest current conditions on the river at a number of locations (indicated by yellow ‘D’ dots on the chart) (‘D’ = Debit – i.e Flow), as well as a Summary and reports of traffic (individual boat names) passing through each of the Rhone locks (ecluses). The real practical problem about the information is that the detailed flow rates are given in cu.m per second, which is not readily translatable into the more familiar knots (or even km/hr) of current. The tendency, increasing or decreasing, is clear, though.
Converting Flow Rates into Current Strengths
A volumetric flow translates into a current according to the profile of the river channel the volume is passing through. So the conversion varies according to the width and depth of the Rhone at any one point at any one time. Nigel Orr’s extremely useful rule-of-thumb is to multiply the cu.m/sec flow under normal (non-flood) conditions (as referenced from the CNR website) by 0.0072 at the northernmost points of measurement (Lyon region) and by 0.0036 lower down (from Valence to Beaucaire). The result is in km/hr. Divide by 1.85 to get the current in knots.
Place and Time of Year – Average Knots of Current
|All of the above average current figures (knots) are approximate and for rule-of-thumb guidance only|
* ‘Chute’ below Pierre Benite (Lyon) ecluse.
** Understates the current’s effect between Beaucaire and Tarascon (in our opinion)
*** The approximate flow rate to current strength multipliers apply to ‘normal’ river level conditions and hence become inaccurate at maximum water levels.
The above table has been constructed from Nigel Orr’s data, taken from Rhone records from 1920 to 1996. It is intended to provide at least an idea of conditions in familar knots units, albeit very approximate. Averages are averages and it would be possible for current speeds to be less than the minima or greater than the maxima – the difference between the two for any one month is between 4 and 7 knots.
Months that normally have current rates noticeably higher than the mean (roughly 3 to 3.5 knots) are January and February; with the month of May also often experiencing higher rates due to the combination of Spring rainfall and Alpine snow-melt. The summer months, sometimes through into October, normally see the quietest conditions, below mean (as one might expect) – but again, conditions on the river can change quickly because (a) the Rhone receives and funnels rainfall from a wide catchment area and (b) the action of opening or closing sluices in the various barrages along its length quickly affects the relevant canalised section. Wet and windy conditions in Winter bring the additional hazard of logs, branches and other detritus speeding down the river and its tributaries.