Advection Fog Wind Question

[Crashnburn]

I'm working my way through Rod Machdo's Private Pilot Handbook and Workbook, and there's a question about advection fog. Specifically, wind speed. The book says winds up to 15 knots tend to mix and deepen advection fog, and the workbook says 5 knots.

I've done some poking around but didn't find anything specific about wind speeds.

Does anyone here know what the wind speed should be?

Thanks

 

[BillTIZ]

18.1.1.1.2 Advection Fog
Advection fog (see Figure 18-5 and Figure 18-6) forms when moist air moves over a colder surface and the subsequent cooling of that air to below its dewpoint. It is most common along coastal areas, but often moves deep into continental areas. At sea, it is called sea fog. Advection fog deepens as wind speed increases up to about 15 kt. Wind much stronger than 15 kt lifts the fog into a layer of low stratus or stratocumulus clouds.

FAA-H-8083-28 Aviation Weather Handbook

 

[flyingron]

I always like the student advection fog where warm, moist knowledge flows over the student's cool dry brain.

Much as I love Rod, his material is riddled with little errors like this, but I don't think it much matters as they're not going to quiz you on 5 vs 15 on the test.
15 knots is a generally accepted value as being the top end of fog formation. 5-10 is prime to cause advection fog.

 

[Racerx]

I wouldn't get too worried about the minutiae of wind speeds. Just know what advection fog is and when/where you'll see it. Warm air over cool surface.

 

[Crashnburn]

Thank you, all.

Edit. I’m really surprised at the maximum wind speed for mixing. 15 knots is pretty stiff.