Yesterday I was planning on taking off just a little while before sun set to get in a few take offs and landing, then as it got darker and darker to end up doing a few nights take offs and landings.

What this was going to involve was taking off and landing during the daylight hours then continue flying thru “civil twilight”, where it’s the light we see after the sun is below the horizon and can last anywhere between last 20-35 minutes after sunset. Nigh flying is defined as that performed between the end of evening civil twilight and the beginning of morning civil twilight.

With that said, only take offs and landing’s an hour after sunset or before sunrise count toward maintaining nighttime currency. And if you intended to take a passenger with you to view the sunset from above it’s important to note that to be current for night landings with passengers, a pilot must have done at least 3 full stop landings between the times of one hour after sunset and one hour before sunrise within the last 90 days. Whew!

A least that was my intent, but Mother Nature had other ideas.

Fog – Fog is a natural weather conditions that can cause visibility to become zero. First it is important to understand that fog is basically a cloud on the ground.

Did you know that there are 8 types of fog?

Mist and Fog are the terms used to describe low visibility caused by water droplets suspended in the air. Fog is effectively surface cloud and has a significant impact on the conduct of flying operations, particularly landing and take-off. Different types of fog are defined according to how they are formed.

(BTW: The only difference between mist and fog is visibility. It is called fog when visibility is .6 mile or less and called mist when visibility remains above 0.6 mile. In driving term’s, it tends to be referred to as fog when visibility is about 330 feet or less.)

Steam Fog: This type of fog is commonly seen in the Great Lakes but can be seen on any lake. This forms during the fall season. As summer ends, water temperatures don’t cool right away but air temperature does. As a mass of dry, cold air moves over a warmer lake the warm lake conducts warm, moist air into the air mass above. This transport between the lake and air evens out. This corresponds to the second law of thermodynamics and this law state “any two bodies that come into contact, the system will become equilibrium state.” Steam fog does not become very deep but enough to block some of the sunlight.

Radiation Fog: This fog forms when all solar energy exits the earth and allows the temperature to meet up with the dew point. The best condition to have radiation fog is when it had rained the previous night. This makes it easier for the air to become saturated and form fog. However, the winds must be light less than 15 mph to prevent moist and dry from mixing.

Precipitation Fog: This is fog that forms when rain is falling through cold air. This is common with a warm front, but it can occur with cold fronts as well only if it’s not moving too fast. Cold air, dry at the surface while rain is falling through it evaporates and causes the dew point to rise. This saturation forms fog.

Advection Fog: This type of fog forms from surface contact of horizontal winds. This fog can occur with windy conditions. Warm air, moist air blows in from the south and if there is snow or cool moisture on the ground it will meet the warm, moist winds. This contact between the air and ground will cause the air blowing in to become cool. Then dew point rises and creates high humidity and forms fog.

Upslope Fog: This fog forms adiabatically. Adiabatically is the process that causes sinking air to warm and rising air to cool. As moist winds blow toward a mountain, it up glides and this causes the air to rise and cool. The cooling of the air from rising causes to meet up with the dew point temperature. Fog forms on top of the mountains.

Valley Fog: Valley fog forms in the valley when the soil is moist from previous rainfall. As the skies clear solar energy exits earth and allow the temperature to cool near or at the dew point. This form deep fog, so dense it’s sometimes called tule fog.

Freezing Fog: Freezing fog occurs when the temperature falls at 32°F (0°C) or below. This fog produces drizzle, and these tiny droplets freeze when they meet an object. But at the same time there is sublimation going on.

Ice Fog: This type of fog is only seen in the polar and artic regions. Temperatures at 14 F (-10°C) is too cold for the air to contain super-cooled water droplets so it forms small, tiny ice crystals.

Trivia Comment: Did you know that If you were to fill an Olympic sized swimming pool with fog and then somehow condense it, you would be left with around just over 2 pints of water?

So, what does that have to do with my story of not flying last evening?

You’ve heard it again and again… Flying in foggy conditions provides challenges to pilots that are only experienced a few times a year. Flying Visual Flight Rules (VFR) into Instrument Meteorological Conditions (IMC), meaning cloud layers below 1,000 feet above ground level (AGL) and/or visibility less than 3 miles, especially if you’re a non-instrument rated pilot and not  current. So, this was my reason not to go flying last evening.