Weather

Warm, dry weather conditions dominate in the Desolation Sound area during May through September. Mean temperatures are 72F (22C) to 78F (25C) and rainfall averages are: May 1.5"; June 1.4"; July 1.1"; August 1.7"; September 1.8". Fog is uncommon in the Strait of Georgia in the summer months.

Weather in Desolation Sound is quite consistent June through September, mild temperatures with winds rarely in excess of 25 knots. However, Southeasterlies can arrive with little warning. They will not last long (usually a system will pass in 24 hours) and do not necessarily bring rain. Check the VHF weather broadcast daily, but also remember that if systems decide to move quickly they can be hard to forecast. CHECK THE SKY TOO.

** 24 hour weather broadcasts are available on VHF WX Channel #1 for our area (also on broadcast channel #21) **

Vancouver, BC, Canada

  Jan Feb Mar Apr May Jun
Avg. High
42 F
46 F
49 F
54 F
61 F
66 F
Avg. Low
32 F
34 F
36 F
40 F
46 F
51 F
Mean
37 F
41 F
43 F
48 F
54 F
59 F
Avg. Precip.
5.90 in
4.90 in
4.30 in
3.00 in
2.40 in
1.80 in
             
  Jul Aug Sep Oct Nov Dec
Avg. High
71 F
71 F
65 F
56 F
48 F
43 F
Avg. Low
54 F
55 F
50 F
43 F
37 F
33 F
Mean
63 F
63 F
58 F
50 F
43 F
38 F
Avg. Precip.
1.40 in
1.50 in
2.50 in
4.50 in
6.70 in
7.00 in

Summers are hottest in BC's interior, particularly in the south where temperatures frequently surpass 30C (86F). Nearer the coast, temperatures range from 22 to 28C (72 to 83F). Recommended clothing for both regions in summer is the same: shorts, short-sleeved shirts and light dresses in daytime and sweaters and trousers in the evenings. 

Summer Weather

In the summer months (May to September) the frequency and severity of the storms are much reduced. Low pressure areas usually remain offshore as the Pacific High strengthens and moves further north. This northward shift causes the main storm track to shift into the northern Gulf of Alaska and across northern British Columbia. South of this track, minor frontal systems, upper troughs and thunderstorms produce most of the weather. In August and September, weeks can pass between weather systems.

Summer fronts

During the summer months, fronts tend to approach the coast from the northwest across the Gulf of Alaska.Over the northern coastal areas, the front is usually accompanied by a narrow band of cloud and light rainfall. Southeast winds will tend to increase along the coast just ahead of the front, then shift into the northwest with its passage. As the front continues southward and presses further into the Pacific High, the rain area often disappears and the clouds begin to dissipate.

As the front moves inland, it is weakened by subsidence to the lee of the Coast Mountains.

Thermal Troughs

The usual summer pressure pattern has a high pressure area over the eastern Pacific and troughs of low pressure in the southern interior of BC This trough forms due to prolonged heating and is referred to as a thermal trough. The effect of this trough is to create a light, disorganized wind pattern as air flows toward the hottest locations. Along the coast, light winds in the morning are replaced by strengthening inflow winds during the afternoon and evening in most inlets and valleys, as the cool coastal air is drawn towards the interior. Locations in BC with marked inflow winds are the Strait of Juan de Fuca, Portland Inlet, Howe Sound, through the Hope area and up the Fraser Canyon.

On occasion, during the summer the thermal trough will move out from the interior and onto the coast.When it does, it normally lies over Georgia Strait causing subsident outflow winds from the interior which gives clear skies and light winds along the coast.

After a few days, the thermal trough will shift back into the interior causing westerly winds of 20 to 30 knots through Juan de Fuca Strait and into southern Georgia Strait. Sea fog and stratus will accompany these winds and may extend as far as Vancouver Airport and Boundary Bay. In the strongest cases, the fog will lift into stratus and spread up the Fraser Valley to Hope.

Cold Lows

A cold low is a large, nearly circular area of the atmosphere in which temperatures get colder toward the centre of the low, both at the surface and aloft.While a surface low pressure centre is usually present beneath the cold low, its true character is most evident on upper charts. The significance of cold lows is that they produce large areas of cloud and precipitation, tend to persist in one location for prolonged periods of time and are difficult to predict.

Cold lows can occur at any time of the year, but the most frequent occurrence, know as "cold low season," is from the end of May to mid-July. At this time, pools of cold air break away from the Aleutian Low and move southeastwards to take up a nearly stationary position off the British Columbia or Washington coast. Once established, the cold low will generate a series of upper cold fronts which will rotate across southern British Columbia. The overall effect is to produce a widespread area of cool, unstable air in which bands of cloud, showers and thundershowers occur. Along the deformation zone to the northeast of the cold low, the enhanced vertical lift will thicken the cloud cover and can produce widespread precipitation. In many cases, the deformation zone is where widespread and prolonged thunderstorm activity occurs. Eventually, a strong system will approach from the west and will have sufficient strength to force the cold low inland, usually in the form of a strong upper trough. A favourite track is across the northern United States, but alternate tracks are across southern British Columbia or even northeastward along a line from Seattle to Fort St. John. As it crosses the area, widespread cloud, showers, thundershowers, or even steady rain can occur for a period of 24 to 48 hours. Normally, while the original cold low is moving off, the next one is already moving across the Gulf of Alaska on its way to take up residence off the coast.

TIDES

The Flood and Ebb tides meet in Desolation Sound coming north from the bottom of Vancouver Island and south from the top of the Island. The result is almost no current in the Sound. The most you will see is 1.5 knots. As you will see, however, there is a tremendous vertical drop, up to 18 feet. Great care must be taken when navigating and anchoring.

About Tidal Rapids

Most tidal rapids can be run with safety from 30 minutes before slack water until 30 minutes after slack water. Some can be run as much as an hour before or after. If the difference between high water and low water is small, certain rapids may be safe for an entire tide. But if the difference is large, those same rapids may be dangerous at any time other than a very few minutes on either side of slack water.

In major rapids, it is common for the current to increase until it no longer is a smooth, laminar sweep, and becomes a boiling, crashing, upwelling maelstrom that looks exactly like a fast-falling whitewater mountain stream. White water is full of air, and less buoyant than green water. Boats float lower. Rudders lose effectiveness and propellers lose bite. When diminished buoyancy and lessened control are combined with strong currents, standing waves, deep whirlpools and boils of upwelling water, very quickly you can have a recipe for disaster. This is why good boats are lost in tidal rapids.

While the time and duration of slack water varies with the individual rapids, each rapids is quite consistent within itself. By long observation, relationships have been established. For example, slack water at Malibu Rapids, at the entrance to Princess Louisa Inlet, occurs 35 minutes after low water at Point Atkinson, and 25 minutes after high water at Point Atkinson. Other rapids, such as Deception Pass, Seymour Narrows, Yuculta Rapids and Dent Rapids, have their own current tables that predict the times of turn and maximum current. Mariners experienced in these waters have those tables and live by them.

We have enormous respect for tidal current rapids, and will not run a major rapids except during the narrow window of time that surrounds slack water. We study the current tables and make our travel plans with any rapids topmost in our minds. This book reflects our cautious approach. We discuss the various rapids frankly and without sugar-coating, and hope our readers will take our cautions seriously.

Robert Hale