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Look out for Fog
 It was a great boating Summer, after a rocky start in June and early July. However, now we begin the Fall and Winter boating season, which has its own attractions.
Those crystal clear, still days on the uncrowded local waters are balm for the harried soul. However, they can also "re-harry" your soul with little mercy if some simple precautions are not observed in your planning for a day or weekend trip.
Remember that once we hit November, Environment Canada does not issue Small Craft Warnings. Understand what the weather is really doing, and pay attention to the actual and forecast winds in conjunction with the tides. Also recognize that weather system changes can occur rather more quickly with less forecast reliability than during the summer. Watch for building pressure gradients particularly with big Highs in the cold interior and an offshore Low, as very strong outflow winds can ruin your whole day. Monitor your barometer for significant drops in pressure, and head for home.
OK, so back to that ideal clear, still, bright winter day, and the trip to False Creek, Snug, or Gibsons for the obligatory $300.00 hamburger. The possibility of fog is one of the concerns which should be uppermost in your mind. Apart from checking the marine forecast and actual weather, check to see whether fog had formed overnight, and then dissipated before you arrived at the marina. This would have been radiation fog, formed when the temperature dropped to the dew point overnight. Bear in mind that the air mass picks up moisture and condensation nucleii under stable conditions, and the period of clear weather is reduced each day the stable conditions prevail. If you try and use all the daylight to stay out, you may find as the heat of the day wanes late in the afternoon and the temperature drops, the dew point will have climbed and fog will reform before you are back at the dock. This time will be earlier each day.
Best preparation is to check the previous evening's temperature/dewpoint spread, and today's forecast spread on the Weather Channel or the Text Forecast at
www.weatheroffice.ec.gc.ca. Better yet is to select "Aviation Weather" on this website, select the METAR/TAF box, select "plain language" and insert CYVR (Vancouver airport) in the "get the bulletins" box. This will give you the last three hours of actual temperature/dewpoint and limits to visibility, and a forecast for the next 24 hours, which will include the time when any fog is likely to form and the visibility in that fog. Just remember that this information is for the airport, and other local conditions may vary so be conservative.
Fog can materialize from another source. In clear conditions, and with a light southerly wind which brings relatively warm and moist air up the Strait, advection fog can form as this air is cooled by the cold water. This can be a real bummer, as this fog will not necessarily dissipate with daytime sun, and could stay in place until the next frontal system comes through. You may have seen such a fog bank as it moves in to cover English Bay and insinuate itself through First Narrows. If you are in Snug when that happens, you may have an extended holiday, or a ferry and bus trip home!
P/Cdr John Northey AP
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