Vertical Visibility

VV (Vertical Visibility)

Even San Diego, California sees fog. In fact, the entire coast of California can me mired in advection fog - from San Francisco to the Baja Peninsula. When a warm moist airmass moves over the cold upwelling coastal waters fog will form. The west coast people like the term "marine layer" to describe it. 

Even San Diego, California sees fog. In fact, the entire coast of California can me mired in advection fog - from San Francisco to the Baja Peninsula. When a warm moist airmass moves over the cold upwelling coastal waters fog will form. The west coast people like the term "marine layer" to describe it. 

During a recent class teaching Air Canada new hires, I was asked whether VV (vertical visibility) constitutes a ceiling. I replied with an unequivocal, “Yes!”

During the good ole days, much discussion transpired on this when a low layered cloud, such as fog or snow was observed as –X (partially obscured) or X (obscured). This changed years ago with the term “VV” (vertical visibility). Back then, you would have heard the acronym WOXOF (indefinitely obscured at zero feet and visibility zero statute miles). The forecast, written as COXOF (ceiling forecast of zero hundred feet and visibility zero), would always get a few snickers as it sounded like “cocks off.”

Here is the ruling from Environment Canada’s MANOBS.16.3.9.4 Vertical visibility (VV) shall be reported when the sky is obscured and information on vertical visibility is available. The existence of a vertical visibility will constitute an obscured ceiling. Vertical visibility shall be reported to the nearest 100 feet from the surface. Following are two examples:

METAR CYDF 182100Z 25005KT 1/4SM +SN VV002 M02/M02 A2926 RMK SN8 SLP911

Translation: Deer Lake, Newfoundland is getting hammered in snow with the laser ceilometer seeing about 200 to 250 feet into the snow. As a FYI, if you want to guess the accumulation, invert the prevailing visibility of 1/4SM to get 4 cm/hour accumulation.

The vertical visibility in Kingston, Ontario is observed as 250 feet in fog by a ceilometer. The observer rounds it to VV002. METAR CYGK 241800Z 23005KT 1/4SM FG VV002 09/09 A2936 RMK FG8 SLP963

For obscuring phenomena forecasted in a TAF, the cloud group is replaced with the vertical visibility group. (MANAIR 2.6.11) It basically means how far up into the grey, unlit, opaque, featureless cloud a person will see. Of course, this is a different story when a pilot looks down with lights acting as a depth provider. That VV003 in snow may sometimes mean you will see the ground at 700 feet or higher. The weather guy thinks from the ground up. You as a pilot will observe differently from above. Transport Canada and lawyers may think even differently. LOL