Mountain Weather: When to Go for the Summit
by Alasdair Turner
AAI Instructor and Guide
The answer to the question of whether or not to leave camp for the summit can sometimes be obvious, such as on a morning that greets us with high winds that knock us off our feet or with a flash of lightning that allows us to momentarily see our partner's face while still motionless inside a sleeping bag. However, it is much more difficult in less extreme scenarios. What should you do if you wake to a clear morning with high clouds and a light wind? Or what if on a windless morning, dense fog envelops the tent?
The weather must always be taken into account when leaving for a summit attempt. Unfortunately, weather changes, and in the mountains it often changes faster than we can react, causing potentially dangerous situations. By using a combination of simple weather knowledge, familiarity with local weather, and flexible schedules and routes, we not only increase our safety when going to the summit, but increase the chances that we will get there. (It goes without saying but I'll mention it as a side note anyway that awareness of weather must be combined with solid navigation skills, knowledge of self-rescue, and well-founded decision-making abilities to ensure the safest climbing trip possible.)
Weather patterns are completely different from one mountain range to another. Some ranges always give good warning of impending poor weather; others give none. It is beyond the scope of this article to try to explain weather patterns or list the different types of weather that are possible in the mountains. There are many good books on the market that offer pictures of different cloud types and give explanations of what they might suggest for short-term weather. Start by picking up one of these books and becoming familiar with what different types of clouds can signal. Without being able to identify some types of clouds, it can be difficult to predict short-term weather patterns.
Cumulus clouds rise over Camp Muir on Mt. Rainier, just two hours before a major thunderstorm hit the area.
Being prepared is one of the most important parts of any climbing trip. Your planning process should include acquiring a current weather report. In addition to getting the latest weather forecast before I leave for a trip, I always carry a small mp3 player with a built-in radio and use it every day for updates on the weather.
One important thing to remember about weather forecasts is that often they are created for population centers and don't necessarily describe the weather anticipated for your climbing location in the mountains. Accurate weather reports for mountain ranges often can be difficult to obtain. If you can only get one for lowlands nearby, keep in mind that when a moving air mass is confronted by mountains, it is lifted up and cooled in the process. If clear air cools to its saturation point - clouds form, and if cloud masses cool - rain may fall. Cloudy but dry weather in the lowlands may translate to wet weather in the mountains when it arrives.
In addition to my mp3 player, I also like to carry a barometer (or barometric altimeter), such as the Suunto Vector. Changing barometric pressure can signal changing weather. Rises in pressure and high pressure systems tend to bring more stable, dryer air. Drops in pressure and low pressure systems often signal a trend towards moist, cooler air. In the northern hemisphere, high pressure systems move in a clockwise direction and low pressure systems move in a counter-clockwise direction. Bear this in mind if you are looking at satellite imagery as part of your pre-trip weather planning process. Which direction a particular system is moving and where it is at in relation to a coast, body of water, etc. will make a big difference in what sort of weather - precipitation in particular - may be headed your way.
Remember, altimeters measure altitude by reading the barometric pressure. An increase in your altimeter signifies a drop in barometric pressure. For example, waking up the morning of a summit climb and finding that your barometric altimeter has you 200 feet closer to the summit than when you went to sleep is a sign that the pressure dropped during the night. It is always a good idea to keep track of barometric pressure changes over the course of a trip. Also, you must remember to recalibrate your altimeter regularly at known elevations! GPS units measure altitude by either barometric pressure OR by satellite triangulation, so make sure you know how your GPS measures altitude and read it accordingly (with adjustments for barometric pressure changes if necessary).
Often, high winds aloft can be a sign of more serious weather moving in soon. Lenticular clouds forming on a mountain top signal that wind is pushing moist air over the top of the peak. Snow plumes coming off a high ridge are also a way to tell if it is windy above your position or on the other side of a ridgeline or terrain feature.
Lenticular clouds near the summit of Mt. Baker, indicating a moisture system moving in.
Even if you have armed yourself with the knowledge and tools suggested above, the decision to leave for the summit is still not always an easy one. The first thing I consider in questionable weather is the commitment of the route. If the weather does turn bad, how difficult will it be to get down? If the route is very difficult to descend, consider taking a different route or waiting for the weather to improve.
Mountaineering is not a sport for people with non-flexible schedules. Earlier this summer on a planned climb of the North Ridge of Mt. Baker, I got several weather reports predicting incoming bad weather and observed a drop in pressure overnight. I woke up to perfect blue skies, light winds, and very warm temperatures. Although this would seem to suggest we leave for the summit and do the planned route, we chose not to climb the North Ridge due to the weather forecast. Instead, we headed for the standard route. Once we got to the summit the weather very quickly changed, and we descended in near whiteout conditions. If we had decided to do the North Ridge, we would have had no choice but to continue up in very poor, potentially dangerous conditions.
Questionable weather does notalwaysdeteriorate. I nearly always get up on time and am ready to go even when I got o bed with doubts about the weather. Oftentimes, there is no reason a climbing party can't complete the non-technical, early sections of a climb in poor weather with the hopes that the weather will improve. Several years ago in the Southern Picket range of the North Cascades, I woke up to what appeared to be very poor weather conditions. With the knowledge that we would likely have to turn around, we continued to the base of the technical climbing anyways. Once there, we were still not sure if the weather was going to improve or deteriorate. We sat down for a half hour and waited to see what the weather would do. It slowly improved, so we decided to go for the top. The views from the top that day were, and still are, some of my most memorable in all my trips to the Cascades.
Walking the summit ridge of McMillan Spire in the Southern Pickets in a very short weather window between storms.
Mountain weather is notoriously difficult to predict, and even with no signs of bad weather, climbers must always keep it in the back of their minds. As with many other things in climbing, the more you know, the safer you are likely to be, and by arming yourself with the knowledge mentioned in this article and always carrying a barometer and radio, you will increase your chances of getting to the summit. Additionally, becoming interested in and observant of how weather patterns affect the specific mountain range in which you climb can be your best tool against getting caught in a storm unexpectedly.
Finally, be sure you are always thinking about a contingency plan, your descent options, and the commitment factor while you are climbing so that you limit the risk of getting stuck in an unpredicted storm, unprepared and unaware. A major part of alpine climbing is limiting your exposure to the objective dangers, such as storms and foul weather. Going to the mountains prepared for any and all conditions and with an appropriate level of knowledge and decision-making ability for your objective, is the most effective way to limit those risks.
Recommended Reading on Mountain Weather