Red sky in the morning, sailor take warning.

[Gargleblaster]

We had a beautiful red sky this morning while I was walking the dog. It got me to thinking - I have seen lots of red skies in the morning at sea and have never had a particular problem with the weather following one. I have had lots of problems with the weather when there has been no red sky. I can understand why the shepherd should delight in a red sky at night but not why a sailor should take warning from a red sky in the morning. Can anyone enlighten me?

 

[Evadne]

Basically, our weather moves from west to east so if you can see the sun rise and it is (redly) shining on clouds, they are coming our way. If you can see the sun set, then the clouds are either overhead or exiting to the east and the weather is clearing up. I think.

Or for today's generation:
Red sky at night, barn's alight
Drowned sheep in the morning, global wwarming.


http://www.theweatherprediction.com/habyhints/139/ (wonderful thing, Google). /forums/images/graemlins/smile.gif

 

[Rustyknight]

I have a book called "Weatherwise" which compares some of the old style weather lores, and gives them a reliability rating.

For the red sky one, it gives an excellant rating.

[ QUOTE ]
Given a lurid red sunrise, always forecast the probability of wind and rain later in the day. There are six possible permutations all to do with a bright red sunrise and with wind behaviour at the time:-

1 With a veering wind: short outbreaks of rain, temporary lull in the wind followed by clearer skies, showery outbreaks and wind squalls. Note that if the morning sky perceptably lowers and becomes ever more gloomier, a major deterioration is possible.

2 With backing wind: rain imminent (probably only a few minutes away, strengthening winds- probably F5-7, maybe even stronger.

3 With westerly wind; rain probable within ten to fifteen hours on average, sometimes much sooner dependant on the amount of red in the sky: the angrier and redder the sunrise, the closer the rain and wind are likely to be. Wind will increase and back accompanied by a fall in air pressure: barometer falling 1-2 millibars in three hours indicates probable future wind strengths of F4-6: barometer falling 3 millibars or more in three hours presages stronger, maybe gale force, winds

4 With southerly wind: sky will become overcast within about four hours (maybe sooner) bringing continuous moderate rain and backing, increasing wind within about five hours on average.

5 With easterly wind: mainly cloudy, periods of rain and drizzle which could persist throughout the day. No significant increase in wind strenght.

6 With northerly wind: rain showers, increasing at first but dying away around noon. Wind will be gusty at first, falling during the afternnon as cloud cover decreases.

[/ QUOTE ]


So there you have it! /forums/images/graemlins/laugh.gif

 

[Cruiser2B]

It has more to do with the relative differences in refractive indices of dry and moist air. If the light is coming from a less refractive medium (drier air) to a more refractive medium (moister air) it will bend more, so that instead of seeing the usual blue component of the light, you'll see the red component. If the approaching air (in the West) is 'wetter' than the air in the east, the sunrise will be red - more moisture is a good indicator of bad weather, but not always so. Conversely, if the air to the West is drier, then that would indicate the weather will clear up and the sunset will be red. All 'active' weather is driven by moisture in the air. Moistness is not an absolute figure, but simply relative to the surrounding airmass.

Kevin

 

[Evadne]

Well, I don't think it's got anything to do with refraction, as the atmosphere isn't really homogeneous enough to act like that, more likely diffraction or scattering. According to the met office:
The sky appears red due to dust particles or dry air. As English weather systems move mostly from west to east, a red sunrise indicates dry weather moving away to the east, so rain should be expected soon. Conversely, a red sunset hints of dry weather to come from the west.
But I suspect you could think up lots of reasons why it happens, and all would have an element of truth in them.

 

[Cruiser2B]

[ QUOTE ]
As English weather systems move mostly from west to east, a red sunrise indicates dry weather moving away to the east, so rain should be expected soon. Conversely, a red sunset hints of dry weather to come from the west.


[/ QUOTE ]
Sounds a lot like what I said.
As for the atmosphere not being homogenous enough for refraction to occur, how do you explain rainbows then?

 

[Gargleblaster]

The result of our red sky this morning in deepest Buckinghamshire, at 1530 hours there has been negligible wind and occasional patches of rain. Of course maybe the warning to sailors only applies on the coast. Or mainly the warning is that as the result or our red sky this morning there was no wind today. I know a bit of rain has never worried me or caused me to feel warned. At least he shepherds can sleep soundly tonight with no prospect of frost, but I don't think they are going to get a red sky as there is too much cloud.

 

[Sinbad2222]

No it has nothing to do with refraction. It arises from the scattering of light from the billions of tiny particles in the atmosphere. These particles scatter blue light more than red, this is why the sky looks blue - because we are looking at the scattered blue light. It follows therefore that if the blue light is lost by sideways scattering then the effect on the direct light from the sun will be to make it look red.
At dawn this red direct light fom the sun in the east will give a reddish reflection off the clouds in the west which is where our weather tends to come from, so the clouds (and possibly rain) will arrive later in the day.
At night the sun sets in the west and, in the absence of clouds in the west, the clouds in the east will be bathed in the red light from the sun and (there are no clouds in the west) a good day should follow.

 

[Rustyknight]

Curiously enough, the Met Office has Strong wind warnings in force (F6-7) from St Davids Head in Wales, right round to the Wash and beyond....... with possible F8 in places.

Of course, this evenings forecast could change. /forums/images/graemlins/wink.gif

 

[Evadne]

Thankyou for the illuminating and accurate explanation. /forums/images/graemlins/smile.gif
Can I claim to have Lakesailored myself?

 

[Lakesailor]

I think you'll find that comes under Rule 7, Rogue Lakesailoring

http://www.lakelandimages.co.uk/lakesailor/rules/

 

[Rustyknight]

Good thing you names not Roger! /forums/images/graemlins/laugh.gif

 

[oldharry]

I always understood the evening red sky to indicate that there was no significant weather pattern to the west where the weather usually comes from, so its likely to remain settled, while a red morning sky indicates that cloud and unsettled weather is moving over the area, so may well become worse.

But it doesnt always work:

This:

and this:

were followed the next day by this:

and this:

... and yes the sky really was that colour - one of the worst duststorms in the Canaries in recent years, and which spread right across the Atlantic to the South American coast. And of course it came from the East, not from the west

 

[Sinbad2222]

The wind does not always come from the west of course, this is when the rule breaks down.
Ask most people what the prevailing wind in the British Isles is and they will say, correctly south west, but in fact statistics tell us that south westerlies occur only 35% of the time - it's still the prevailing wind though!

 

[Cruiser2B]

In the Canaries, aren't the prevailing winds Easterly? If so, then you should reverse the rule. Properly though the red sky is only indicative of relative moisture, not dust. Winds can be driven by other than frontal systems, such as catabatic winds like sciroccos.

Kevin

 

[Cruiser2B]

[ QUOTE ]
At dawn this red direct light fom the sun in the east will give a reddish reflection off the clouds in the west which is where our weather tends to come from, so the clouds (and possibly rain) will arrive later in the day.
At night the sun sets in the west and, in the absence of clouds in the west, the clouds in the east will be bathed in the red light from the sun and (there are no clouds in the west) a good day should follow.

[/ QUOTE ]

Err, the red sky in morning is in the East, and the red sky at night is in the West. Look at the photos above and the red sky is clearly around the sun, not on the clouds on the opposite side of the sky. Also the sun emits light over the entire spectrum, so "direct light from ths sun" being red is twaddle. Look up "refraction".

Kevin

 

[Sinbad2222]

I don't need to look up refraction I have a Masters degree in Physics.
Read my posting carefully. Yes, of course the direct light from the sun is white - I didn't say it was not. What I said was that that white light with blue subtracted from it (due to scattering not refraction) appears red. Have a read of any elementary Physics textbook or look up Wickipedia if you cannot grasp that.
Of course the red sky in the morning is in the east to us but it west as far as the sun is concerned. This is because the sun is further away from us than the clouds are - Got it?

 

[tcm]

Re: Red sky in the morning, Kent\'s on fire.

.

 

[Cruiser2B]

[ QUOTE ]
Of course the red sky in the morning is in the east to us but it west as far as the sun is concerned. This is because the sun is further away from us than the clouds are - Got it?

[/ QUOTE ]

Too bad you don't have a masters in English. The sun doesn't have a West, nor does it have an East. If the sun is to the east of us, from where we are standing on the earth, then the sky to the east of us is red. None of it is west; not west of us and not west of the sun - the sun doesn't have a west.

You claim that we see red, because the blue light is subtracted - that would only make sense if we consistently saw red skies at sunrise and sunset, as the depth of atmosphere does not vary day to day. Also if the blue light had been removed from the light, then the sky opposite the sun would also appear red (as the blue light is no longer there), but this is not the case. If you pull your head out of your elementary Physics text and look out the window, that would be evident.
As you are obviously referring to "Rayleigh scattering" you no doubt realize that it is defined by an equation using 'refractive index' as a constant. So Rayleigh scattering is a form of refraction.

If your 'scatterring theory' made sense then pictures of the earth taken from space would be blue, but in the pictures I've seen the clouds are white. Since the light passes through hundreds of kilometres of atmosphere (and billions of particles according to you) including the return trip after being reflected from the clouds, then why doesn't it scatter and show as blue?

 

[oldharry]

[ QUOTE ]
In the Canaries, aren't the prevailing winds Easterly? If so, then you should reverse the rule. Properly though the red sky is only indicative of relative moisture, not dust.
Kevin

[/ QUOTE ] Yes - winds generally north east, but dont try telling the locals the red sky wasnt dust....:

However, red light from a low sun can be caused by filtering effect of the presence of water vapour, clouds, pollution such as smoke, dust, or anything in the atmosphere which reduces the blue UV element of sunlight while allowing the redder colour elements through.