How to Predict the Weather without Instruments or Forecasts
Be that person everyone admires in nature
There is something majestic about a person who can forecast rain. I had a friend that could do it reliably — now and then, he would lift his head, sniff comically and announce that it would rain in an hour or so. And sure enough, a little over 60 minutes later, it would start raining.
He claimed he could smell the rain.
After doing a bit of research, I discovered that he wasn’t being eccentric, at least not when it came to smelling rain. It turns out that plants ‘dump waste’ when there is a low-pressure system inbound. That waste smells a little like compost or freshly cut grass.
This revelation prompted me to investigate other methods of predicting the weather without the help of modern technology. Partly because it’s interesting to see how we humans managed before the days of blue screens and grey suits, partly because I am insatiably curious, but mostly because I want to impress my son when we’re in the wild — nothing says “hero” like theatrically predicting the weather…and being right.
Forecasting the weather isn’t that hard either. Well, not when keeping predictions to the following 36 hours. Interestingly, even weather bureaus can’t predict beyond 15 days with decent accuracy.
It all boils down to pressure. So you want to find indicators for whether the pressure is high or low. The prevailing heuristic is “if pressure is high, let the good times fly; if pressure is low, life’s full of woe.” Credit to me for the rhyme.
But why is pressure so integral to the weather?
For those of you that are just here for the punchline, skip to “Forecast Indicators” below — no judgement. For those of you that have children with Nested-Why Syndrome, here’s why pressure systems are so important in weather prediction.
In the above image, the airflow (yes, that’s what the arrows indicate) moves slightly inward with low-pressure systems, and slightly outward with high-pressure systems. This causes excess air in a low-pressure system and a deficit in a high-pressure system. As you would expect, as air moves into a low-pressure system, it can’t go through the ground and is forced up where it’s a lot cooler. The cold then condenses the air moisture into droplets, which can lead to precipitation.
The next thing to know is that the weather comes in from the west. This fact makes the adage “red sky at night, sailor’s delight; red sky in the morning, sailor’s warning” true.
When the sun sets in a red sky, it means that there is a lot of dust in the atmosphere there (the west). The light is refracted by the dust and only red light, which has the longest wavelength, manages to get through the crowded air. The other colours have shorter wavelengths and disperse. This is an indicator of high air pressure and stable air in the west, which is moving east.
When the sun rises in a red sky, basically the opposite is true. The high-pressure system has passed and is already in the east. This could mean that a low-pressure system is following, which can bring rain.
Forecast Indicators
Right, so now we’ve just got to figure out how to tell if there is a low-pressure or high-pressure system about.
Wind
The wind is the movement of air from — you guessed it — a high-pressure system to a low-pressure system.
Quick side note: know how winds are named. It’s always based on the direction it’s coming from. Winds from the west are called westerly winds, and so forth. A great way to remember it is thinking about it as we do with people. If you’re from the West, you’re a Westerner.
Westerly winds mean that there is a high-pressure system in the west and a low-pressure system in the east. As mentioned, weather comes in from the west, so this likely means that the bad weather is already passed.
Easterly winds, however, mean that the low-pressure system is still in the west, along with the bad weather — all coming your way.
So all we have to do is figure out where the winds are coming from and we will have a good idea about the coming weather. Watch the direction of smoke, lick a finger and hold it up, or do like the Fly-Halves do and throw blade of grass in the air — any of these methods will tell you which way the wind blows.
Air
Low pressure causes plants to release their waste creating that fresh cut grass cross compost smell. If you’re near a swamp and smell sulphur, it’s swamp gases being released for the same reason.
High humidity also usually precedes a storm. Watch out for pinecones; if they open up, humidity is low, but if they’re closed, it’s high. Wood swells up when humidity is high, as will long hair — the reason people complain about frizzy hair at the coast is the humidity.
Animals
Of course, the entire animal kingdom was blessed with the ability to predict the weather, even insects, while we have to rely on them for clues. While there are many old wive’s tales as to why they know of impending disasters and extreme weather, it turns out they are just sensitive to pressure differences.
Cows will spread out if there is the promise of good weather but will huddle when bad weather is en route. The tighter the huddle, the worse the weather. They will also be restless in a barn, lie down in their pastures, or be stingy with their milk when bad weather is afoot.
Birds fly low when a storm is brewing because the low pressure hurts their ears. They will also sit on telephone, or electricity wires when pressure is dropping. Seagulls will stop swarming and relax on the beach, and sparrows will stop chirping. Birds will also generally wait out a storm to collect food, so if it’s raining and they’re still grabbing worms, you know it’s going to be a long storm. If you catch them flying in formation for migration, however, it means the weather is going to be good for the day — they don’t like long trips in bad weather.
And cats, well, they clean their ears when a storm is approaching. Those aloof little bastards.
Insects are also sensitive to pressure changes. Bees will stay near their hives and butterflies won’t venture when there’s rain coming on the day. Ants stay near their anthills and will typically make steeper mounds if there is rain due. Spiders will reinforce their webs — you can tell by the increase in the number of cross-sections, provided you count them normally and know what the baseline is. Yeah, me neither.
If you have crickets and a calculator, you’ll be able to tell the temperature, usually within a degree. Count the number of chirps in 14 seconds. If you’re looking for Fahrenheit, add 40. For Celcius, add 8, multiple it by 5 and divide by 9. For the first time, Celcius is the more complicated one.
Coffee cup
This is my favourite. After you pour a cup of coffee, monitor the bubbles. If the bubbles rise to the rim of the cup, it indicates a high-pressure system and good weather in-coming, and for the next 12 hours — all good to go hiking. If they gather in the middle, it indicates a low-pressure system and bad weather.
I tested this one this morning, noticed that my coffee had bubbles in the rim, and impressed my wife with a bold prediction that it would clear up later in the day without looking at the forecast.
Sky
We already know about the sailor’s warning and delight, but there are other tells…and rhymes.
“A rainbow in the morning gives you fair warning”. When the sun is in the east, and a shower is in the west, a rainbow can manifest. I can’t help myself.
A night with clear stars is a night with clear skies. It means that there is less moisture in the air and nothing to keep the warmth in. This indicates that it will be a cool night and a fresh morning.
Fog in the summer usually means a clear day. The air is too cool to evaporate water so it condenses instead. If the air is cool, there is likely no clouds.
My son has an insatiable love for the moon. So I had to include this one. A ring around the moon is caused by moonlight refracting off of the ice particles in the cirrostratus clouds — clouds that are high and sometimes transparent — which often precedes a warm front and can mean rain or snow in the next 36 hours.
“A ring around the sun or moon means rain or snow is coming soon”.
A double halo usually means strong winds in the coming storm.
Clouds
And then, of course, there are the clouds. Generally, clouds get lower as bad weather approaches, and go higher and spread as the weather clears.
But, if you’re like me and want to go into more detail…
Cirrocumulus
Description: long rows of puffs. Sometimes, they manifest in lines that look like scales, hence the term “Mackerel Sky” that you may have heard sailors or fisherman mention.
Forecast: fair but cold weather. A Mackerel Sky usually precedes strong winds.
“Mare’s tails and mackerel scales make tall ships take in their sails”. More about the “Mare’s tails” later.
Altocumulus
Description: high clouds caused by rising currents in the cloud that meet the unstable air above them.
Forecast: rain within 36 hours.
Cumulonimbus
Description: big towering clouds that go straight up into the air.
Forecast: thunder, lightning, and heavy rain.
Cirrus
Description: highest type of cloud and look like wispy feathers.
Forecast: fair weather when moving west to east. A lot of them can mean an approaching frontal system which brings cold weather. And if they’re low and look like a horse’s tail it means bad weather. A mare is a female horse.
“Mare’s tails and mackerel scales make tall ships take in their sails”.
Nimbostratus
Description: low-hanging, grey, sad clouds like you find in London.
Forecast: long term rain. And sadness.
Cumulus
Description: cotton-ball-like puffs of cloud.
Forecast: no immediate rain, but can cluster into rain clouds.
Cloud Colour
- Black: storm, with no strong winds.
- Brown: storm, with strong winds.
- Gray: light, usually long-term, shower.
- Green: hail.
And that’s about it. I know this is a longer article, but the intention is to create a resource that you (and I) can easily refer back to. The thinking is to give it a quick once over before you go hiking or any other venture into the great outdoors, memorise the salient points, and impress your company.
For now, though, we’re in lockdown. And the forecast remains grey.
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