A Climber’s Guide to Field Meteorology

Cerro Escuela

The Northern Patagonian Ice Field, as seen from the summit of Cerro Escuela (Photo by Barrett Dickey)

Deep within the vast, purgatorial dominion of the Northern Patagonian Ice Field, weather is a matter of the utmost importance. Having spent the better part of three months on that godless plateau over three separate expeditions, I learned the art of weather prediction at the School of Hard Knocks.

Truth be told, we had it pretty easy due to the daily weather reports that would reach us via the magic of satellite technology. Each day, at the appointed hour, the team would nurture a fragile wisp of hope as a cryptic series of alphanumeric characters was received. Our hope was generally unwarranted.

If you’re not in possession of a sat phone, much less a permanently staffed basecamp from which such helpful dispatches might be sent, how can you remain forewarned of unfavourable weather whilst on expedition? The answer is to make field observations and here I present a few simple ideas to instantly upgrade your status from “wet chump” to “amateur meteorologist”.

Wrap your head around Global Weather Patterns

Let’s start with a disclaimer – I am merely a humble climber, not a meteorologist. Given that I haven’t spent years at university studying this discipline, what follows is a luddites understanding of weather patterns. For most of us, this should prove sufficient. I’m always open to further illumination from anyone with the qualification to provide it.

To the untrained eye, weather can appear to be chaotic and random, but pay attention and you’ll soon discern some method in the madness. Of course, some geographical locations are harder to predict than others – one gets the feeling that meteorologists in Scotland rarely get it wrong with a prediction of “wet with a chance of fookin’ shite”, whereas the complex effects of various mountain ranges can make Alaskan forecasts a bit of a crapshoot.

But what is weather, and why does it occur? On a very basic level, weather is simply the interactions of disparate air masses. Two main things make these air masses move – the Coriolis Effect and pressure differentials.

The Coriolis Effect is three things:

  1. The force of the Earth’s rotation
  2. A really useful fact for pub trivia, and
  3. A potentially decent band name

It seems counter-intuitive, but the rotation of the Earth causes air to be deflected in opposite ways in the two hemispheres. You can see this in action yourself. Take a cup or a can or a loaf of bread or whatever and rotate it in one direction. Look at it from the top down, then whilst still rotating in the same direction, look at it from the bottom up. It turns the opposite way, right? SCIENCE! This is why cyclones spin the opposite way from hurricanes, and it also gives rise to prevailing winds – trade winds and westerlies.

Anyways, it gets a bit more complex than that. Basically, uneven heating of the Earth’s surface causes pressure gradients. Air from high pressure areas naturally moves toward low pressure areas. High pressure systems are associated with fine, dry weather whereas low pressure systems are associated with unstable conditions and precipitation. Isolated pockets of high and low pressure move about all over the shop, but certain latitudes tend to feature one or the other predominantly – that is why when you look at a map of the world, you can pick out roughly lateral bands of desert (around the 30 degree mark) and forests (at 60 degrees and the equator) circling the globe.

Simple, right? Not really. Not even close. I’ve deliberately left a lot of information out of this explanation, but with these two concepts alone, we can glean a decent understanding of why global patterns occur on a macro scale – most notably, we can infer a wet or dry climate and the direction of prevailing winds.

Get some Local Knowledge

Forearmed with the above information, you can take a (very rough) guess as to what sort of climate you’ll experience depending on which part of the world you’re in. But that’s painting it in very broad strokes, and doesn’t consider a whole raft of other variables that can affect what type of weather you can expect – seasonal variation and geographical influences (e.g. mountains) not least of these.

The best information you can get your grubby mitts on will come from the locals – they’ve seen it all, year after year. Take my home town of Brisbane, for example. Ask anyone what you can expect out of the weather in the summer months, and they’ll tell you the same thing – a hot, muggy day with a thunderstorm at 4pm, sometimes with hail. This phenomenon is so predictable you can set your watch by it. If a storm cell is green when it comes over the Great Divide, get your car undercover and expect your social media to go apeshit.

Every region has its own specific pattern, so take some time to pick the brains of the locals, especially those whose career revolves around the weather – farmers, pilots, firefighters, rangers and mountain guides all tend to be comprehensive weather almanacs. Which direction does the wind come from on the Kahiltna Glacier? What month does the rainy season start in the Cordillera Blanca? What’s the coldest month in the Canadian Rockies? The locals know all this and more, and besides, the weather is one of those bullshit icebreaker/small talk topics, so it’s an easy conversation to get started.

Wind Directions

A base camp on the Kahiltna Glacier (Source: RMI Expeditions)

When I attempted the West Buttress of Denali in 2015, our team noticed something strange at Ski Hill – all the tents seemed to be on the wrong side of the accompanying wind walls. Maybe they knew something we didn’t, we mused, and decided to ask the ranger on duty, whom we’ll call Danger Dave.

“Which way does the wind come from here?” I asked.

“From up glacier, from the west,” said Danger Dave.

“Ok, that’s what we thought. Why have all the other groups put their tents on the wrong side of the walls?”

“Because they’re all morons.”

That was a fair call, because the signs were there for all to read – the dominant wind direction was westerly, and these winds would be funnelled down the glacier toward the camp. In addition, the tell-tale arrows of sastrugi were abundant. When the katabatic winds began to blow everyone else back toward Talkeetna, we were snug behind our modest snow wall.

Understanding the global weather patterns can help you guess where the winds are likely to come from, but there are other local signs too.  As mentioned above, sastrugi often form as small arrows on snow and ice, pointing toward the direction from which the winds come. Trees can often grow with a lean where strong winds are prevalent, with the notable examples of Patagonia and the West Coast of New Zealand coming to my mind.

But some regions have extremely variable winds, and weather reports or simple observations will prove useful. Once you know where the wind is coming from, you can set your camp accordingly and guess what type of conditions it might bring – for example, in Peru, is it coming from the arid west, bringing warm, dry conditions? Or is it coming from the east, bringing all the moisture from the Amazon? The type of conditions the next few days might have in store can often be guessed from this one simple clue.

Cloud Patterns

High winds will often bring specific cloud patterns, and these can also be used to predict the incoming weather. That said, it’s not an exact science, and I’d say the reliability of this observation alone is about the same as Shane Watson’s batting was. But it’s part of the puzzle, and when taken with other signs, can help you make somewhat informed decisions.

These Mare’s Tails were observed at Mt Arapiles and were followed my moderate precip.

The first thing you will see are high, wispy cirrus clouds known as Mare’s Tails. These look like the thin strokes of an artist’s brush, and they signify strong winds high in the atmosphere. Sometimes, they are followed by a patchy overcast that has the appearance of cotton balls. Sailors called this phenomenon Mackeral Sky, because apparently it looks like fish scales, but you should take with a grain of salt any comparison that was made by the same folks who thought that dugongs looked like smoking hot half-fish ladies. In any case, if you see these cloud formations in sequence, it’s usually a pretty decent indicator that precipitation can be expected within 48 hours. Or, according to ye olde wisdom of the sea, “Mare’s Tails and Mackeral Scales make small ships carry low sails”.

This Mackeral Sky was observed just south of Santiago de Chile. It was followed by cool, overcast conditions but no precip.

The last thing you want to see are lenticular clouds, which look like UFO motherships hovering over mountain peaks. These are created by strong winds blasting over the summit, condensing into cloud, and then continuing on their merry way on the other side. If you see these, battern down the hatches, because shit’s about to get real.

This mahoosive lenticular was observed at The Keyhole at the edge of the Northern Patagonian Ice Field. Shit did indeed get real.

Barometer Readings

I don’t have a fancy Suunto watch, so I don’t usually use this observation, but it’s certainly pretty useful. Try to get one of the models which display a graph rather than a number alone. A barometric pressure reading is pretty much useless on its own, but in the context of a graph, it can be revealing. A slow but constant pressure decrease should make you alert but not alarmed, whereas a rapid decrease might see you manning the nearest nuclear bunker. Don’t forget that air pressure naturally decreases as you gain altitude.

Summary

Once again, I’m no professional weather man and I don’t do “Waistcoat Wednesday” like that pelican on the ABC. But I have found these tips useful in predicting weather in the field, and I hope you can put some of these tools to use during your adventures as well.

Ryan Siacci, Esq.
September 2018

Thoughts? Opinions? Cries of dissent?