Weather observations and the coming storm
With reference to the post I wrote on coastal weather patterns, this weeks storm is an illustration of a winter front. However, the public forecasts and the rainfall warning are clearly geared toward the sea-level public. So where does a backcountry enthusiast go to get information on the weather and the snow? The information sources for a backcountry enthusiast are wide and varied. The weather resources page at the CAA contains some of the links.
My opinion is, don’t waste your time on the various advanced weather plots, satellite, radar and infrared animations of various levels unless you’ve studied meteorology; almost everyone who tells you they understand them is lying - they are nice for pretty pictures and for one-upping your friends on what a weather geek you are, but they are very complex and beyond the scope of what can be expected from a backcountry recreationalist. If you insist on trying to read the satellite imagery, at least read the CAA’s tutorial; they also point out the problem with untrained users attempting this.
Taking a page from Malcolm Gladwell’s book Blink, the amount of information you need to make your backcountry travel decisions is surprisingly small. Rather than complicating things with enormous reams of information that is hard to interpret, rely on experts to boil it down for you, and rely on your own observations in the field to make decisions based on what is actually happening.
Weather information takes two primary forms; observations, which include webcams, satellite, and snow pits; and forecasts, including weather forecasts, and avalanche bulletins which attempt to forecast snow conditions over a wide area. Your observations of weather and snow also fit into these two categories – the immediate observations of current conditions, and your predictions of what will happen in the next 4, 8 and 16 hours.
Get your weather information as close to the source as possible; Environment Canada has the sensor network and the meteorologists who provide most of the weather data and interpretation for other web sites, most of which re-hash the data. Supplement this with weather information as close to the geographic locale you are visiting; with wide differences in altitude, and distance from the coast, comes differences in freezing levels and winds, so an overview forecast is often not enough, since Environment Canada’s main customers are the general public and industries that are not as concerned with mountain weather as you are
Similarly, get snow information as an overview from the CAA, and supplement that with information as close to the area you’re going as possible. The most reliable sources for mountain conditions in the are the CAA, the various ski hills, parks (both Provincial and Federal), where avalanche experts observe the weather and the snow, and often publish their results.
There are other, less reliable sources such as internet forums that provide more anecdotal information; be wary of these since many providers are working very hard to use jargon in order to seem as “plugged in” as possible. In addition, these forums are convoluted, unorganized and difficult to use; at best they contain reliable data using standardized language that is easy to understand, at worst they are full of partially understood terms, poorly recorded observations, and argumentative one-upmanship with little actual use other than to boost participant’s egos..
For Coastal BC, I find it very useful to get a synopsis of the weather systems and when they are expected to make landfall. Day to day weather forecasts more concerned with the sea-level public and whether or not it will rain; the synopsis tells you what systems are approaching the coast. From a high-level, each system approaches, makes landfall, and moves on. The timing of the movement of these systems, where they track, and how much precipitation they deliver, is where the uncertainty of a forecast lies. Knowing what systems are expected rather than the specific probabilities of precipitation is more useful because one you are in the mountains you’re more than likely cut off from the source of information. Observing when a system has passed can tell you weather it’s moved through faster or slower than usual.
A ridge of high pressure over the British Columbia interior will continue to give strong to gale force outflow winds for the mainland inlets tonight through tomorrow.
The first of two frontal systems that is currently over the offshore waters will continue to spread gale force southeasterlies offshore and to most of the northern and central waters tonight. Storm force southeasterlies will continue along the west coast of Vancouver Island, Western Queen Charlotte Sound and the southern half of West Coast Charlottes tonight.
Winds will ease slightly overnight before a second frontal system arrives Tuesday morning spreading gale force southeasterlies again to the previously mentioned regions. Gale force southeasterlies will also develop over the northern strait of Georgia and Eastern Juan de Fuca strait late Tuesday afternoon.
It’s a good overview, but notice it says nothing about freezing levels, or amounts of precipitation; mariners are not concerned as much with rain and snow as they are with wind and visibility.
The rainfall warning for today’s storm reads :
40 to 70 mm of rain is expected for metro Vancouver, Howe Sound and Sunshine Coast through Tuesday. 80 to 110 mm of rain is expected for West Vancouver Island through Tuesday.
This is a warning that significant rainfall is expected or occurring in these regions. Monitor weather conditions..Listen for updated statements.
A nearly stationary frontal system will spread rain into the South Coast of British Columbia tonight through Tuesday. 40 to 60 mm of rain is expected for metro Vancouver, Howe Sound, and Sunshine Coast through Tuesday. Rainfall up to 70 mm is possible for parts of metro Vancouver near the north shore mountains through Tuesday.
Strong southeast winds up to 90 km/h will develop along the front over west coast Vancouver Island Tuesday. Southeast winds up to 80 km/h will develop over the exposed coastal sections of East Vancouver Island Tuesday.
The strong winds are expected to ease late Tuesday night into early Wednesday while the rainfall will continue to affect the south coast through Wednesday.
Notice the language used in this text and all weather texts is very standard and clear, with all terms used being simple, easy to understand and having a clear interpretation. Also note that although rainfall amounts are forecast, the freezing levels are not.
The short term text forecast for the south coast of BC reads:
Rainfall warning in effect.
Tonight..Cloudy with 40 percent chance of showers this evening. Periods of rain beginning late this evening. Amount 10 mm. Becoming windy near midnight. Temperature steady near 7.
Tuesday..Rain at times heavy. Amount 10 to 20 mm except 30 mm near the North Shore. Windy. High 10.
Tuesday night..Rain at times heavy. Amount 10 to 20 mm except 30 mm near the North Shore. Windy. Temperature steady near 8.
Rainfall warning in effect.
Tonight..Cloudy. 40 percent chance of showers early this evening. Periods of rain beginning this evening. Amount 10 mm. Windy. Low plus 4.
Tuesday..Rain at times heavy. Amount 20 to 30 mm. Windy. High plus 4.
Tuesday night..Rain at times heavy. Amount 20 to 30 mm. Windy.
Temperature steady near plus 4.
Tonight..Cloudy. 60 percent chance of flurries late this evening and overnight then wet snow beginning. Temperature steady near zero.
Tuesday..Wet snow changing to rain near noon. High plus 3.
Tuesday night..Rain or wet snow. Temperature steady near plus 1.
Again, this is a forecast for sea-level. Useful for wind and precipitation, but not for snow and freezing levels, which are essential for mountain travelers. So where to find the freezing levels?
There is a “high elevation (seasonal) forecast” which is geared toward driving. This might be useful for information on the Coquihalla Summit area, or the road you are using the access the backcountry, but little else.
The CAA Avalanche Bulletin has the freezing level information built-in, often in addition to the weather synopsis, and more, in their weather forecast section:
Tuesday and Wednesday: Inland areas are expected to get 20-30cm of new snow each day, while coastal areas could get twice that. Freezing levels around 1500m for Tuesday and 1000m for Wednesday. Moderate to strong southeasterly mountaintop winds easing Wednesday evening.
Thursday: Cloudy with a few lingering flurries, bringing another 3-5cm inland and 10-15 to the coast. Freezing levels near 800m and moderate southeasterly mountaintop winds.
You can also find an alpine forecast at Whistler’s site. This forecast used to be a specific product offered by Environment Canada; now it appears to have been provided by a contractor called Mountain Weather Services. Mount Seymour used to have a similar page tailored for the North Shore; now their alpine weather links to a site that doesn’t show the provenance of their information.
Now we have our information. I have to say that most of what we need is in the avalanche Bulletin, as the CAA does an excellent job of bringing in the weather components.
Observe that the freezing levels are forecast to drop throughout the storm from 1500m to 800m, getting lower toward the end of the storm, with precipitation also easing off at the same time. The storm is coming in warm, and cools at the end. The hazard is highest near the end of the storm when the maximum amount of snow has fallen, but the snowpack has not had time to settle. This corresponds with an avalanche hazard of High for the alpine and treeline, where snow will be falling at the height of the storm. As Thursday rolls around the storm will have mostly passed, and the avalanche cycle should have cleared the High hazard.
However, noting the synopsis we read in the Marine forecast, there are in fact two frontal systems. What we have to watch for, if we head out, is a delay in the approach of the second system. This would mean that the snow falling tonight would settle tomorrow, and the second system could extend the period of high hazard to Wednesday. We also have to watch for a change in wind direction since an outflow condition is specifically mentioned.
With regard to changing weather with changing locales, it’s important to notice how different the avalanche bulletin for the North Shore is. There is less hazard (considerable trending to low) since the mountains there are maximum 1300m high, and most of the snow will fall above that elevation in the beginning of the storm, the hazard is much reduced. This is not to say that that hazard is negligible; as I’ve written before, the rainfall which will no doubt fall to the peaks of all of the north shore mountains will freeze in the evenings, and provide a very hard surface if there is clear weather after this storm.
Also note that even though many will argue this point, the North Shore mountains do not contain alpine terrain as defined by the Avalanche association;
Treeline ratings are applicable to the transition area between densely forested areas below and alpine regions with few or no trees above, also known as sub-alpine. Trees are generally smaller and are found in non-contiguous stands separated by open, wind-exposed areas. The treeline zone is a relatively narrow band compared to below treeline and alpine.
Alpine ratings are applicable to areas above the treeline. Small, isolated trees may be found at the low end of this elevation band but they quickly give way to large expanses of open slopes leading to ridges and peaks. This entire band is highly exposed to the effects of wind.
The very peak of some of the North Shore mountains may be considered just peeking into the alpine region.
- Subscribe to the CAA bulletins via RSS,
- Peruse the archive of past bulletins
- use the CAA’s trip planning tool
- take the CAA’s inline avalanche course
- Another recommended Satellite imagery tutorial
- Marine Synopsys from Environment Canada
- Whistler/Blackcomb Avalanche Bulletin
- North Shore Avalanche Bulletin
- South Coast Avalanche Bulletin
What weather sources can you recommend? Comment below.