What's this cold, wet, white stuff that's piling up all around us? Ah, yes. I remember. It happened last year at this time, too. Winter recreating and climbing on Mt. Rainier can be really enjoyable. However, a thorough weather forecast is very important.
Here are some thoughts on the weather and Forecast Resources.
To most people, weather is something you look up at from ground level. To climbers, pilots, and other people who get outdoors, the weather can be above you AND below you. You're often IN those clouds that others are looking up at in the city. What to the sea level viewer is a cloud is fog to you!
It's VERY important to have a good weather forecast when you climb Mt. Rainier. The weather rules the day and will rule your climb, especially this time of year. The weather has proven itself to be one of the biggest contributing factors to situations requiring rescues.
Here are some of the websites that I religiously check before my climb, and before I register climbers. In general, you should be particularly concerned about clouds, precip., temperature, and winds.
Mt. Rainier Recreational Forecast
For a good and quick weather briefing, start off with the Mt. Rainier Recreational Forecast. It's specific to Mt. Rainier and put out by the forecasters at the National Weather Service forecast office in Seattle. This usually gives the freezing levels, too.
UW Atmospheric Sciences GFS Forecast Models
Instead of portraying atmospheric information on a horizontal plane, the following site loops at 3 hour intervals and shows a vertical slice of the atmosphere from the Mt. Rainier area in a southwest direction. On the left are pressure-altitudes. Although the altitude at which a specific pressure is encountered will vary depending on current atmospheric conditions, at "standard" pressure, 1013 mb is sea level, and 1000 mb is roughly 360', 900 mb is about 3,240', 800 mb about 6,400', 700 mb about 9,500', and 600 mb is about 13,800'. Consider that Paradise is at about 5,500', Muir at 10,000' and the summit at 14,411' and you will be able to see at what elevations the clouds are forecast to be! Pay particular attention to humidities, as Mt. Rainier tends to intensify already high humidities and produce clouds.
Temperature-Winds Aloft Forecast
Next up is the temperature-winds aloft forecast from the FAA interpreted by usairnet. This is usually for pilots, but climbers would be wise to pay attention to it. Remember, these are theoretical forecasted wind speeds and directions. You can adjust the forecast period at the top of the page. I have found from personal experience that the winds are often greater than forecast and temperatures are warmer.
Another good site to assess regional winds aloft is the wind profiler showing wind speed and direction at Sand Point (Seattle).
Here is a primer in reading this data: Wind is shown in the vertical from sea level to 3,500 meters (about 11,500') given on the Y axis. Data is posted each hour on the X axis with the most recent readings on the left side of the diagram. Time is UTC which is 8 hours later than PST, so 02/18 isn't February 18 but rather February 2 at 1800 hours, or 1200 PST. North is represented by the top of the diagram, south by the bottom, etc. For example, if a line is coming from the left and ending at the vertical time line, that is a west wind (270 degrees). Each full barb on the shaft of a vector represents ten knots, each half barb is 5 knots, and a solid triangle is 50 knots, so a "barb and a half" is about 15knots. Ten knots is about 11.5 mph. Of course local winds may vary, but wind at 10,000' is going to be quite consistent with simultaneous wind elsewhere at that altitude in the region, whether measured at Sand Point or on Mt. Rainier.]
NWAC Mountain Weather Forecast Page
In the winter, the Northwest Weather and Avalanche Center produces the best weather forecast discussion because it is specifically geared toward recreational purposes in the mountains! You can also, of course, read the avalanche forecast here, too.
Camp Muir Live Weather Telemetry
Paradise Live Weather Telemetry
Also, with love from the Northwest Weather and Avalanche Center, I help maintain a weather station at Camp Muir. This is always fun to check. Although the wind instruments often rime up and cease to function, the temps. are usually pretty accurate.
Paradise Experimental Weather Forecast
And finally, here's a page I find extremely useful. It's an "experimental" forecast interpretation based on Paradise.
Get a weather radio, if you can, for getting updates up on the mountain. NOAA weather radio broadcasts decent mountain weather forecasts on 162.425MHz, 162.45MHz, 162.475MHz, and 162.55MHz.
Hope that helps!