Why Does the Wind Sometimes Disappear When It Rains?
The rain starts — and your sails suddenly hang uselessly. Coincidence? Quite often, no.
It is something I have noticed many times while sailing.
You are moving along quite happily. There is pressure in the sails, the boat responds properly to the helm and perhaps you are beginning to think about whether you are on the best tack.
Then the sky darkens.
A few spots of rain appear on the water.
For a moment, the breeze may even strengthen.
Then the rain arrives properly — and suddenly the wind seems to disappear.
The sails go soft. Boat speed falls away. The helm loses its feel.
On an inland river such as the Thames, the effect can be remarkably dramatic.
So is the rain actually switching the wind off?
Not quite.
But the weather associated with rain can substantially change the way wind is transported through the lowest few hundred metres of the atmosphere — and therefore how much of that wind eventually reaches our sails.
Understanding why is useful scientifically.
Understanding what to look for is useful as a sailor.
And sometimes it can even be useful tactically.
There May Still Be Plenty of Wind — Just Not Where You Are
One of the first things to appreciate is that the wind at mast height is not necessarily the same as the wind a few hundred metres above us.
Wind speed generally increases with height because air close to the ground is slowed by friction.
Trees, buildings, river banks, hills and other obstacles complicate things further.
The atmosphere therefore needs a mechanism for continually mixing air vertically.
On a sunny or reasonably warm day, the ground is heated by the Sun. The air immediately above it warms, becomes less dense and rises.
Other air moves down to replace it.
This creates turbulence and convection.
That mixing can bring faster-moving air from higher in the atmosphere down towards the surface.
To a sailor, it appears as the breeze we feel at water level.
Then the weather changes.
A thick rain cloud moves overhead.
Solar heating falls dramatically.
The surface begins to cool.
Rain may cool the air still further.
The lowest layer of the atmosphere becomes more stable.
Vertical mixing decreases.
There may still be a considerable wind above us, but much less of its momentum is being mixed down to river level.
From the boat it can feel as though somebody has turned the wind off.
Why Inland Sailors Can Notice This So Strongly
This effect is particularly interesting on inland water.
At sea, there may be a relatively unobstructed wind extending across a very large area.
A river is different.
On the Thames the wind has already had to negotiate:
trees;
houses;
hills;
river banks;
bends in the river;
gaps between buildings;
woodland;
differences between sunny and shaded areas.
That produces an extraordinarily complicated wind field.
Anyone who sails regularly on a river soon discovers that the wind on one part of the reach can be quite different from the wind only a few hundred metres away.
Sometimes it is different only a few boat lengths away.
Add an approaching rain shower to that already complicated situation and the result can be fascinating.
And occasionally frustrating.
Rain Can Cool the Air
Cloud cover is only part of the story.
Rain itself can contribute to cooling.
Turning liquid water into water vapour requires energy. If some of a falling raindrop evaporates, that energy comes from the surrounding air.
The air cools.
It is the same basic reason that wet skin feels cold when water evaporates from it.
If the air below a cloud is relatively dry, quite a substantial amount of rain can evaporate before it reaches the ground.
This can create a region of cooler, denser air beneath a shower.
That cooler air may descend towards the surface.
And this is where the story becomes more complicated.
Because rain can sometimes reduce the wind we experience — but under other circumstances it can produce a sudden burst of wind.
Sometimes the Wind Increases Before the Rain Arrives
A pattern I find particularly interesting while sailing is that the sequence can sometimes be something like:
Normal breeze → stronger gust → wind shift → rain → lull
That stronger wind immediately before the rain makes the subsequent loss of pressure feel particularly dramatic.
What may be happening is that cooler air is descending beneath the shower.
When this descending air reaches the surface, it cannot continue downwards, so it spreads horizontally.
That spreading air can produce a small gust front or outflow boundary ahead of the rain itself.
The wind at the boat can therefore increase before the actual rain reaches you.
The direction may change as well.
Then, once the shower passes overhead and the local atmosphere becomes cooler and more stable, the surface wind may weaken substantially.
From the sailor's perspective:
The breeze builds.
Something changes.
The rain arrives.
Then the sails collapse.
It can happen surprisingly quickly.
But Do Not Learn the Rule "Rain Means Less Wind"
This is important.
Rain does not automatically mean that the wind will decrease.
A gentle area of persistent rain beneath thick cloud is very different meteorologically from a vigorous convective shower.
A strong shower — and particularly a thunderstorm — can contain powerful descending air.
When that air reaches the surface and spreads out, wind speeds can increase sharply.
There can also be abrupt changes in direction.
So a better rule is:
Steady rain and thick cloud can suppress surface mixing and sometimes reduce the wind at water level.
But:
A vigorous shower can produce strong gusts and rapid wind shifts.
That distinction matters enormously to sailors.
If a dark shower is approaching, assuming "the rain will kill the wind" could be exactly the wrong response.
The correct response is to watch what the atmosphere is actually doing.
A Sailor Is an Extremely Sensitive Wind Detector
There is another reason sailors notice this phenomenon so readily.
We are remarkably sensitive to very small changes in wind speed.
Someone walking beside the river might barely notice the difference between an 8-knot and 4-knot breeze.
In a sailing dinghy, the difference is enormous.
At 8 knots the sails have pressure.
The boat accelerates.
The helm has feel.
The crew can trim against a meaningful load.
Drop that breeze to 3 or 4 knots and everything changes.
The sails begin to hang.
The boat loses speed.
The apparent wind changes.
Steering becomes less effective.
On a river, current adds another complication because the water can continue carrying the boat even when there is very little useful wind.
You can suddenly find yourself moving in a direction you had absolutely no intention of going.
Watch the Water, Not Just the Sails
One of the important steps in becoming a better sailor is learning to stop looking exclusively at your own boat.
Your sails tell you what the wind is doing now.
The river ahead can tell you what the wind may do next.
That distinction becomes very important when showers are moving across a sailing area.
Look upwind.
You may be able to see darker patches of water where increased wind is roughening the surface.
You may see smooth patches indicating very little wind.
Look at the trees.
Are the tops beginning to move more strongly?
Is movement starting on one bank before the other?
Look at the rain itself.
Is it approaching as a broad grey area?
Or is there a clearly defined, dark shower cell?
Can you see a curtain of rain beneath one part of the cloud?
And most importantly:
Which direction is it moving?
You are gradually building a mental picture of what may arrive at the boat several minutes later.
That is an important transition in sailing.
You stop merely reacting.
You begin anticipating.
The Shower May Change the Wind Direction as Well
The most interesting part for a racing sailor may not be the change in wind speed at all.
It may be the change in direction.
Cooler air descending beneath a shower can spread outwards when it reaches the surface.
The wind you experience therefore depends partly upon where you are relative to that outflow.
A shower passing to one side of the river could alter the wind direction without necessarily passing directly overhead.
This creates the possibility of a sequence such as:
gust → header → rain → lull → lift
Or:
gust → lift → rain → header
The atmosphere has no obligation to arrange itself conveniently for the sailor.
What Are a Header and a Lift?
These are two extremely useful sailing terms.
A lift is a wind shift that allows you to steer closer towards your destination while maintaining the same relationship between the boat and the wind.
A header does the opposite.
Imagine you are sailing close-hauled towards the next mark.
If the wind shifts in your favour, the boat can be pointed more directly towards the mark.
You have been lifted.
If the wind shifts the other way, you must turn away from the mark to keep the sails working efficiently.
You have been headed.
And here is the interesting part:
Exactly the same wind shift can be a lift for one boat and a header for another boat sailing on the opposite tack.
That is why a relatively small wind shift can completely alter a race.
Imagine Two Boats Approaching a Shower
Suppose two boats are beating up the river.
One is on starboard tack.
The other is on port.
Ahead is an approaching shower.
The air spreading from beneath that shower causes the wind direction to rotate.
For one boat, the new wind direction might be favourable.
Its bow can come closer to the mark.
Lift.
For the other boat, exactly the same change may force it to point further away.
Header.
That can turn a small meteorological event into a tactical opportunity.
The clever decision is not necessarily:
"Which side of the river has more wind?"
It may be:
"Which side of this shower is likely to give me the most useful wind direction?"
That is a much more advanced way of looking at the river.
Champagne Makes These Changes Particularly Interesting
Sailing an A-Rater such as Champagne makes these changes especially noticeable.
A boat with a large sail area and a tall rig responds very visibly when the pressure changes.
When the breeze is there, the boat comes alive.
There is load in the sheets, pressure through the rig and a very obvious sense that the sails are producing power.
When the breeze disappears, that power can vanish remarkably quickly.
And because river racing involves trees, bends, buildings and highly localised patches of wind, it encourages you to look beyond the boat.
Where is the next breeze?
Where is the dark water?
What are the boats ahead doing?
Has somebody twenty boat lengths away suddenly heeled?
Has a boat on the opposite bank stopped?
Is a rain curtain moving across the reach?
The answer may be more important than another tiny adjustment to the sheet.
Sometimes Another Boat Is Your Best Weather Instrument
One of the most useful things to watch is not the cloud.
It is another sailing boat.
Suppose a boat 200 metres ahead suddenly heels over.
You may have just been given advance warning of a gust.
If its crew suddenly eases the mainsail, that is another clue.
If three boats ahead all stop almost simultaneously, the breeze may be collapsing ahead of you.
If the boats on one side of the river continue moving while those on the other side stop, you have learnt something potentially extremely useful.
You do not need an electronic weather station to see any of this.
The entire fleet becomes a network of wind sensors.
Experienced sailors are constantly collecting information from it.
Rain Can Also Change Your Apparent Wind
There is another subtlety.
The wind your sails experience is not simply the true wind blowing across the landscape.
It is the apparent wind created by combining the true wind with the boat's own movement.
As the boat slows during a lull, that apparent wind changes.
The sails may therefore require retrimming even if the true wind direction has not changed very much.
This helps explain why a boat can suddenly feel particularly lifeless after the breeze decreases.
You have lost some true wind.
The boat slows.
That alters the apparent wind.
The sails lose still more effective pressure.
The response can feel disproportionately large.
What Should You Do When the Wind Dies in Rain?
The first answer is:
Do not panic and do not immediately start making enormous control movements.
In very light wind, excessive steering creates drag.
So does unnecessary movement by the crew.
Try to keep the boat balanced and moving.
Ease the sails sufficiently to preserve their shape and telltales, but do not simply let everything flap.
Avoid repeatedly moving the rudder from side to side.
Keep looking for the next patch of wind.
And remember that the lull may be temporary.
The temptation is to react to the wind you have just lost.
The better sailor starts looking for the wind that is coming next.
And What If the Shower Is Strengthening the Wind?
Then the priorities change.
A dark, vigorous shower deserves respect.
Before it reaches you:
make sure sheets are clear;
ensure the crew are ready;
check that everybody understands what may happen;
be prepared to ease the mainsail;
keep the boat balanced;
maintain a good lookout;
avoid becoming trapped in a difficult position near the bank or other boats.
If conditions are becoming severe, sailing tactics cease to matter.
Boat control and safety come first.
A shower capable of producing strong downdraughts can generate much more wind than the gentle rain-and-lull effect discussed earlier.
Observation matters precisely because there is no universal rule.
The River Surface Is Telling You a Story
A very useful exercise when sailing is to deliberately spend a few minutes watching nothing but the water ahead.
Try to identify:
Smooth water
Probably very light wind.
Fine ripples
A little more breeze.
Dark patches moving across the surface
Often stronger wind approaching.
A sharply defined line between smooth and rippled water
Potentially a significant change in wind speed.
Different water textures on opposite sides of the reach
The wind may be stronger on one side.
Then compare your prediction with what actually happens when you sail into that area.
You will not always be right.
That is part of the exercise.
Gradually you begin connecting what you can see with what you later feel through the boat.
Start Looking at the Sky as Well
Then add another layer.
Watch the clouds.
Not merely whether they are dark, but how they are developing.
Are they becoming vertically taller?
Is the cloud base changing?
Is the rain concentrated beneath one region?
Is the shower moving across the river or directly towards you?
Is brighter sky appearing behind it?
A sailor does not need to become a professional meteorologist.
But learning to recognise what the atmosphere is doing can make you a much better sailor.
From Reacting to Anticipating
This is one of the themes I increasingly find fascinating about sailing.
Learning to make a boat move is only the beginning.
At first, almost all your attention is inside the boat:
Where is the tiller?
What is the mainsheet doing?
Are the sails flapping?
Which side should I sit on?
As experience develops, your attention begins to move outwards.
You start watching the water.
Then the other boats.
Then the river banks.
Then the trees.
Then the clouds.
Eventually you begin putting all those pieces together.
That is when sailing becomes much more than simply steering and trimming.
You are trying to predict an environment that is continually changing.
So Why Does the Wind Sometimes Die When It Rains?
It is rarely because rain itself has somehow "stopped" the wind.
Instead, several atmospheric processes may be occurring together.
Cloud reduces solar heating.
The surface cools.
Rain and evaporation can cool the lower atmosphere further.
The atmosphere may become more stable.
Vertical mixing decreases.
Less of the stronger wind from above reaches the water.
On an inland river, where the wind is already strongly affected by trees, buildings, banks and local heating, that reduction can be particularly noticeable.
But a vigorous shower can do almost the opposite, bringing descending air to the surface and producing strong gusts and rapid shifts.
That is why the useful sailing lesson is not:
Rain means less wind.
It is:
A shower means something is changing — start looking around.
The Most Important Instrument May Be Your Eyes
Modern sailing can involve excellent instruments.
Wind indicators, GPS, weather forecasts and detailed radar imagery can all be useful.
But there is still an extraordinary amount of information available simply by looking.
Watch the water.
Watch the boats ahead.
Watch the trees.
Watch the rain.
Watch the clouds.
And ask yourself:
What is the wind doing over there — and when is it going to reach me?
Because when rain approaches, the important question is not simply:
"Am I going to get wet?"
It is:
"What is this shower about to do to my wind?"
And if you can answer that question even slightly earlier than the boats around you, you are no longer merely reacting to the weather.
You are beginning to sail it.
Coming up Next
A ten-degree wind shift can be worth tens of metres — without your boat travelling any faster.
Why does the same wind shift lift one boat but head another, and what do sailors mean by “tack on a header”?
Learning to read the wind is the next step beyond simply sailing the boat.
Return to pmrsailing.uk https://pmrsailing.uk/sailing-lessons/How-to-sail-better.html
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