We all have access to detailed and generally very accurate weather forecasts before we head to the mountains. How to best use this information to decide if you're going to leave town or not?
When on a climb, the decision to continue up or head down is often a difficult, subjective and emotional choice. How can you add some objectivity into the process?
The decision / weather matrix below I first saw on the excellent mini-route descriptions published by the Mt. Rainier climbing rangers / National Park Service. (Anyone climbing the more popular routes on Rainier should definitely have a look at these descriptions, you can read more about them at this post.)
And, as mentioned again below, “The matrix was created with input from guides and rangers, and represents cumulative knowledge of thousands of ascents” so this is a well tested tool.
It's pretty simple. Ideally in town before you leave, look at four different weather variables in three different categories, assign them a number, and add everything up. You’ll come up with a point value between 4 and 12. Then, plug that into the bottom graphic, and you’ll land in one of three categories appropriate for your team’s skill level - green, yellow, or red. Use that to guide your decision.
Ideally this happens in town before you leave. If the weather is unexpectedly changing quickly on your climb, you can use this while en route.
Is this a set-in-stone rule for every time on every mountain? Probably not. But, it is a useful tool to add some objectivity into an often difficult process.
(Personally, I know I'm not going to remember all this, so I made a few color photocopies on waterproof paper and have one in the first aid kit and a PDF saved onto my phone. Heck, I may even tape one inside my helmet.)
Here’s a link to a PDF so you can easily print one yourself.
Here’s a description of the weather matrix directly from the climbing guide:
“To assist in making a decision if one should climb based on the weather forecast, we have created this matrix. This Go/ No Go Matrix only takes weather into account for a given team experience level. Other factors such as avalanche conditions, equipment issues, other team dynamics, etc., need to be evaluated as well. The actual number output from the matrix can be a rough guide, but the important part of the exercise is to discuss conditions with your team and arrive at a consensus as to what the experience level of your team is and determine how prepared you are to deal with the forecasted weather. As always, one should choose to turn back if the weather looks to be deteriorating. The matrix was created with input from guides and rangers, and represents cumulative knowledge of thousands of ascents.
Start by going down the gray column on the left. First assess the wind component at either 1, 2, or 3. Then proceed to the precipitation component, add 1,2, or 4 to your running total. Continue down the list, summing all the factors from the four rows. Then place your score in the evaluator tool relative to your team’s experience level. You can see from the below matrix that precipitation and visibility can be showstoppers, certainly on a summit climb, but even for a trip to Camp Muir.
On the lower mountain below 10,000 feet, these weather factors can often be mitigated by equipment and exceptional experience, however, there are far narrower margins of error on the upper mountain for everyone. With weather and navigational concerns, it can become all but impossible to reconnoiter your way and survive.”