Mountain Weather Forecasting

Mountain Weather Forecasting

Mountain Weather

When heading into the mountains, there are many factors which will affect your trip – training, logistics, planning, skills, and more. While we can prepare in advance to control many of these factors, we cannot predict nor change the weather! What’s more, mountain weather is a fickle beast and can constantly surprise even the most prepared climbers. Below we’re going to dive into the basics of what to look for and some of the weather forecast resources we use.

Long-Term Forecasting

While it can be nice to start researching the weather well before your planned climb, remember that weather forecasts will only start to gain precision as you get within days of the start date. It is nearly impossible to access a forecast more than 10 days out. So, if you’re looking at the weather months or weeks ahead, try to look for general trends for the area – monthly highs and lows, average precipitation amounts, and days with or without rain can all be helpful indicators of what weather you might experience.

Below are two weather data sets from North Cascades National Park:

North Cascades average temperatures

North Cascades precipitation data by month.

So: January and December are cold, wet times to climb, camp, or ski in the North Cascades. There will be sunny days, no doubt, but these months will feature more challenging weather patterns for the typical climber. In July and August, we see the driest and warmest conditions for the region.

Short-Term Forecasting

As you get within a few days of your trip, you can use more tools to assess the weather. It can be helpful to look for temperature, chance of precipitation, freezing levels, and large weather system trends. Using a forecasting model for a specific area can be very informative.

For instance, when looking at the weather for an upcoming trip to Mt. Rainier, we often use the Mount Rainier Recreational Forecast. Data from this forecast comes from a weather station on the mountain, and does a good job showing us the specific trends we expect to see. Is the weather getting warmer or colder while we’re climbing? Are wind speeds increasing or decreasing? Here’s a snapshot:

Recreational forecast snippet for Mount Rainier National Park.

You’ll be able to find several things in this forecast. First, a general synopsis or picture of the weather. Next, you can see three days of information on cloud cover, chances of rain/snow, and freezing level. The freezing level tells us the rough elevation where rain becomes snow. Note that snow can fall about 1000 feet below predicted levels, however! This helps us assess snow safety, ease of travel conditions , visibility, and temperature impacts. Farther down the forecast, we can see temperatures for different elevation bands (Summit, Camp Muir, etc.) and the associated wind speed and direction for those same elevations. Remember that while the temperature on Monday at the summit may be 26°F, with a northwest wind speed of 25mph, it will feel significantly colder than just a bit below freezing. This forecast does not show windchill nor adjust for the impact of hypoxia (low oxygen) on the human body.

Another critical note when reading a forecast such as this one is that we are seeing day and night 12-hour average temperature predictions, not actual “high” and “low” temps like you would see with a normal forecast. When air temperatures do not change significantly between day and night, they exhibit a small diurnal range and these averages are more accurate. When temperatures change significantly between day and night, they have a large diurnal range, and thus the predicted night time temperature masks the actual low temperature we can expect to experience. Sometimes, this masking effect can throw off the actual low temperature by as much as 15°F!

But what if you are heading to an area lacking a specific weather monitoring station and forecast? There are still good ways to get the information you need. One website we use for mountains other than Rainier is Mountain Forecast. On this website, you can search for a specific mountain, and thus pull data from nearby weather stations in order to give you a forecast. Below you’ll see an example of the

Mountain Forecast screenshot.

Mountain Forecast display.

You can see a general synopsis at the top of the display for 0-3 and 3-6 days out. Below that, you can see information on cloud cover, wind speed and direction, temperature, and freezing left. On the left side of the page, you can toggle through different elevation bands in order to get a more specific sense of weather at various camp locations, summits, etc. One key limitation to Mountain Forecast, however, is that it gives algorithm-based information pulled from broad weather models. A professional forecaster’s weather forecast for the summit of Mount Baker would likely vary from Windy’s algorithm-based prediction, because weather data always requires some level of interpretation. This is especially true with more active weather patterns or events, like storm systems. Focus on trends, not specifics, when using broad forecast services like Mountain Forecast.

A final tool, which has a steeper learning curve, is Windy. This tool offers an incredible array of information, including comparative weather models and pressure lines. Below you can see a small snapshot of the Pacific Northwest, which shows a low-pressure system off-shore. Low-pressure generally means wetter but warmer weather.

Example low pressure visualization from Windy.

What does it all mean?

You have access to a wealth of knowledge if you look through these different resources and analyze what the weather may do during your trip. Keep in mind that weather forecasts are only guesses, but that they are very useful for informing our choices and ensuring we are best prepared for the mountains. Look at the freezing level – do we need single or double boots? An extra warm layer? Look at how much precipitation is forecast – should I bring a lightweight hardshell, or something more burly and “bombproof”? It is even useful to know that the weather is supposed to be nice. Make sure to pack plenty of sunscreen, sunglasses, and a sun hoody!

Experience will help you make these decisions. However, planning beforehand and then assessing how you felt in the gear you brought will grow your confidence in the relationship between weather and gear needs. So, check the weather (from multiple resources), prepare, and get out there!



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