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I contacted a flight briefer this morning in the San Francisco Bay Area in California. At the time, ceilings at my airport (Palo Alto) had just hit 1000 ft, so the field was (barely) VFR. It is a very common pattern in this area for the ceiling to burn off, become broken, scattered, and then disappear.

The briefer told me there was an Airmet Sierra for IFR conditions and mountain obscuration in force, and that VFR flight was not recommended. When I talked with an instructor at the club, we talked about the specific location of the clouds and decided the whole area would soon be VFR.

Question: should I fly if conditions are clearly VFR but the flight briefer is telling me “VFR flight not recommended”? How should I think through the risk assessment here?

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    $\begingroup$ the SF Bay area gets a marine layer (stratus) many days out of the year that can stretch as far as the East Bay Hills and beyond. Most days, as the sun heats up, the marine layer burns off or retreats towards the coast. Briefers for that area will always say VFR Not Recommended, but if pilots abided by that, nobody would be able to fly for much of the year. $\endgroup$
    – rbp
    Feb 26, 2015 at 23:56
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    $\begingroup$ ...The thing to be careful of in the Bay Area is when the air starts to cool again in the late afternoon -- sometimes as early as 4PM -- the marine layer comes back in, and you can be out of luck trying to gett back in VFR. I've had to come back in IFR (sometimes hard to get a popup) and cancel underneath the layer and fly to my destination airport, and I've also scud run, but only because I know the safe way back in and the safe altitudes (eg the Sunol Pass). en.wikipedia.org/wiki/San_Francisco_fog $\endgroup$
    – rbp
    Feb 26, 2015 at 23:56

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"VFR Flight Not Recommended" is a judgement call made by the flight briefer. It means, as you noted from the AIM, that the briefer doesn't think flying around VFR is a smart idea based on what they're seeing.

The usual reasons for a briefer using this phrase are:

  • The weather is currently below VFR minimums somewhere along your intended route.
  • The weather is currently "Marginal VFR" somewhere along your intended route.
  • The weather is forecast to be marginal VFR or below somewhere along your intended route.
  • Some other adverse condition (like mountain obscuration) exists along your route or in the area you intend to fly.

The briefer's recommendation is just that: a recommendation -- it is not binding. How you evaluate the flight to make a Go/No-Go decision when the briefer provides this recommendation is your choice as pilot in command. You will need to consider why the briefer is telling you VFR flight is not recommended, and apply your own knowledge and judgment.

A couple of examples:

  • If the briefer is telling you this because Airmet Sierra is active for mountain obscuration and you intend to fly through some mountain passes prudence suggests that proceeding VFR into mountains that may be obscured by clouds would be a Bad Idea.

  • If the briefer is telling you this because the weather is currently marginal VFR, but it's forecast to improve and you only plan to shoot a few touch-and-go landings at your home airport you might proceed with the flight anyway.

For evaluating the huge swath of conditions in between those two extremes consider your familiarity with the area (typical weather patterns, topography, obstacles, etc.) and the conditions of flight (especially day-vs-night). Thomas P. Turner's site has a nice set of guidelines which I happen to broadly agree with, but each flight needs to be carefully evaluated to determine if you believe you can complete it safely under the conditions reported to you by the briefer.

The safest approach is obviously to cancel the flight (or complete it under instrument flight rules) if you have any doubt.

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    $\begingroup$ Additionally, the briefer may or may not be geographically located in the same place as the pilot calling the briefer. So the briefer is looking at satellite pictures, and other reported information that may not be up-to-the-minute current, and he is making the recommendation based on that. If you're at the airport, you have the benefit of looking out the window and in the direction you're going to fly. $\endgroup$
    – Canuk
    Jul 31, 2014 at 22:20
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Quoting AIM 7-1-4:

2. VFR Flight Not Recommended. When VFR flight is proposed and sky conditions or visibilities are present or forecast, surface or aloft, that, in the briefer's judgment, would make flight under VFR doubtful, the briefer will describe the conditions, describe the affected locations, and use the phrase "VFR flight not recommended." This recommendation is advisory in nature. The final decision as to whether the flight can be conducted safely rests solely with the pilot. Upon receiving a "VFR flight not recommended" statement, the non-IFR rated pilot will need to make a "go or no go" decision. This decision should be based on weighing the current and forecast weather conditions against the pilot's experience and ratings. The aircraft's equipment, capabilities and limitations should also be considered.

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A 1000 feet ceiling means you can only climb to 500 feet AGL to stay VFR. Maintain that altitude, which on the coast is close to 500' MSL, proceeding inland the ground is climbing rapidly towards you. Rapid deceleration upon contact with the ground might be fatal. VFR not recommended.

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