# Adverse Wind & Fog 15&16

Font Size: Larger /Smaller

Chapter 15

• Types
• Crosswinds
• Gusts
• Tailwinds
• Variable wind
• Sudden wind shift
• The book says you’re most at risk during takeoff and landing
• It also says little planes are affected most

Crosswind

• This wind blows from one side or the other
• Breaks off the landing gear
• Gust
• This is where the wind speeds up suddenly (10kts or more)
• Breaks or bends the spar
• Tailwind
• This wind blows up your tail
• Runs you off the end of the runway or into the trees on takeoff
• A 10% increase in landing speed will result in at least a 21% greater landing distance
• Variable wind/Wind shift
• This is when the wind is variable and is shifty
• Wind shear
• This one is trickier than the rest, it pretends it’s your friend then whammy

• For x-wind use the sin of the angle between the wind and the runway
• Wind 280@20 runway 36
• 360-280=80
• Sin(80)=.984807753 x 20=19.69kts
• For the headwind use the cos of the angle between the wind and the runway
• Wind 280@20 runway 36
• 360-280=80
• Cos(80)=.1736481777 x 20=3.47kts

CHAPTER 16

Obstructions to Visibility

Weather Related Accidents

Categorical Outlooks

• AIM 7-1-7 defines 4 categories:
• LIFR Ceilings less than 500 vis less than 1 mile
• IFR Ceiling 500 to less than1000 vis 1 to less than 3 miles
• MVFR Ceiling 1000 to less than 3000 vis 3 to 5 miles
• VFR Ceiling greater than 3000 vis greater than 5 miles

Visibility

• There are 3 types of visibility:
• In flight
• Slant range
• Surface
• Surface vis in Metars is given in SM
• Flight vis is reported in SM as well
• VFR pilots on average loose control after about 3 minutes

Restrictions to Visibility

• Fog
• Haze and smoke
• Dust and blowing dust
• Volcanic ash
• Blowing sand
• Blowing snow
• Precipitation

FOG

• Defined as surfaced based clouds of water or ice crystals
• Fog is the most common cause of vis less than 3 miles
• Fog can form rapidly dropping vis to less than a mile in a few minutes
• Fog is one of the most hardest weather phenomenon to predict

Fog

• Small temp/dew point is needed
• This usually occurs just after sunrise due to small temp/dew point spread
• 3º and closing usually get fog
• condensation nuclei must be present
• 5/8 to 6 miles is mist BR
• Less than 5/8 of a mile is classified as fog

FOG FORMATION

• 1. Cool air to the dew point
• 2. Add moisture near the ground

Fog Formation Mechanisms

• Warm moist air in contact with cooler ground or water
• Upslope flow causing adiabatic cooling
• Evaporational cooling releasing latent heat
• Surface dew point increasing to temp due to evaporation
• Air flowing over a moist surface (swamp, lake, ocean, rain soaked ground ect.)
• Warm rain falling through colder air
• Combination of any of the above

Types of Fog

• 3. Upslope fog
• 4. Precipitation-induced fog/Frontal fog
• 5. Ice fog
• 6. Steam fog

• Usually relatively shallow
• Also known as Ground Fog
• Clear sky, little or no wind, small temp dew point spread
• Warm moist air over low flat areas
• However it may form in valleys as well
• Areas of cold air drainage lend to formation
• This type of fog forms almost exclusively at night or daybreak
• Look for this fog in the am after an evening/night rain and clearing sky
• Or in winter when it gets warm enough to melt snow cover

• Terrestrial radiation cools the air close  the ground
• Wind of 5 kts or less mix the layers of cool air and deepen the fog
• Calm wind results in transfer through conduction alone resulting in thinner fog
• A wind of +5 kts mixes the moist layers close to the ground with dryer air above preventing formation
• Usually only forms over land because of the terrestrial radiation
• Usually dissipates quickly if the sun comes out or a wind +5 kts picks up
• If high overcast persists it will take longer for the temp/dew point spread to increase

• At night a more complicated process is at work
• The top of the fog more readily emits IR radiation skyward
• Fog droplets absorb some of this IR radiation and reradiate back to the surface
• The ground cools more slowly as a result
• This shifts the max cooling rate to the top of the fog bank
• This results in the fog becoming thicker and lowering vis further

Landing Problems

• On approach this is what you see
• In the flare this is what you see

• Moist air moves over colder ground or water
• This fog is associated with horizontal air mass movement or advection
• The surface over which it moves causes the change in temp
• This is referred to as advective cooling
• Examples of this occurrence is mild humid air moving over snow covered ground

• It also commonly occurs along the coastal areas where warm moist air moves off the ocean over colder land
• Deepens with winds up to 15 kts
• Depends on the wind to exist (5-15 kts)
• More than 15 kts tends to lift it into low stratus
• Moves in rapidly with the wind day or night and more persistent than radiation fog

• A characteristic of the coastal areas of southern California in summertime is advection fog
• It forms as warm, dry air from over the land is moved over the much cooler ocean.
• The cold water chills the air to dew point, resulting in low clouds and fog.

UPSLOPE FOG

• Moist stable air cooled adiabatically as it moves up sloping terrain
• Depends on wind to exist (5-15 kts)
• Mixing of the layers as air is forced up can deepen the fog
• Very dense and can exist at high altitudes along the upsloping terrain
• Unlike radiation fog it may form under overcast skies
• Once the winds stops the fog dissipates

UPSLOPE FOG

• Terrain temp will modify the cooling rate
• Very persistent
• Covers a wide area
• Obscures hills and mountains
• If a downslope wind develops fog will dissipate
• This fog is found along the west slope of the Cascades, east slope of the Rockies and east slope of the Appalachian mountains

PRECIPITATION INDUCED FOG FRONTAL FOG

• Warm rain or drizzle falling through cool air
• Evaporation from the precip saturates the cool air and “poof” fog
• Associated with warm fronts mostly
• May also form along cold fronts and stationary fronts
• Little or no wind
• Extra hazards to look for are icing, turbulence and thunderstorms

PRECIPITATION INDUCED FOG FRONTAL FOG

• Very persistant
• Covers a wide area
• Mostly occurs with warm or stationary fronts
• Fog forms on the cool air side of the front
• Formation ends when the precip stops
• The fog may persist for several hours after precip stops however

FRONTAL FOG

• This is an example of frontal fog, forming in southern Indiana as a warm front was encroaching.
• Warm and humid air was moving north, and running into cooler air.
• Frontal fog is a result of contact cooling between two dissimilar air masses
• While referred to as Frontal Fog it is really a form of Advection Fog

ICE FOG

• Occurs when temp is below freezing and the vapor sublimates directly into ice crystals
• Conditions are similar as they are for formation of radiation fog
• -25º F or colder so usually found in arctic region or colder winter spots

STEAM FOG

• Also known as Arctic Sea Smoke
• Extremely cold and dry air flows over warmer water
• Evaporation and heating from the water causes a rise in humidity
• Heating from below creates instability
• Additionally vapor pressure is high next to the water surface but low in the dry air above
• This sets up a vapor pressure gradient
• This causes streamers to rise up giving the appearance of steam
• Also occurs after a rain on a wet highway
• Low stratus clouds
• hard to predict bases

STEAM FOG

• Most types of fog form in stable atmospheric conditions.
• The exception is steam fog, shown in this picture of Maligne Lake, Alberta, Canada, just after sunrise in late summer.
• The land cools off overnight while the water retains heat from the summer day.
• As the cooled air slips over the lake, heat and moisture are added from below, resulting in a fog that twists and writhes– hence the term “steam fog”.

STEAM FOG

• This type of fog may be persistent
• The larger the lake the more persistent and the more widespread
• Low level convection must be present for formation

MIST

• Visibility from 5/8 to less than 7 statute miles
• Lower Relative Humidity than fog at about 95-99%
• Generally not as restrictive to visibility

HAZE AND SMOKE

• Haze – dry particles not classified as dust or something else
• Occurs in stable air
• Usually only a few 1000 feet thick but may extend as high as 15,000 feet
• Often associated with an inversion which gives it a definite top
• Haze may lead to the illusion that something is farther away than it really is
• Smoke forest fires, industrial areas
• Both can be bad under a temp inversion
• Can cause visual illusions as well

BLOWING PHENOMENA

• Precip- drizzle, rain, snow
• Snow however may present additional problems
• May cause white out conditions or
• Flat light

Flat Light

• Flat light is an optical illusion, also known as “sector or partial white out.”
• It is not as severe as “white out” but the condition causes pilots to lose their depth-of-field and contrast in vision.
• Flat light conditions are usually accompanied by overcast skies inhibiting any good visual clues.
• Such conditions can occur anywhere in the world, primarily in snow covered areas but can occur in dust, sand, mud flats, or on glassy water.
• Flat light can completely obscure features of the terrain, creating an inability to distinguish distances and closure rates.
• As a result of this reflected light, it can give pilots the illusion of ascending or descending when actually flying level.
• However, with good judgment and proper training and planning, it is possible to safely operate an aircraft in flat light conditions.

White Out

• As defined in meteorological terms, white out is when a person becomes engulfed in a uniformly white glow.
• The glow is a result of being surrounded by blowing snow, dust, sand, mud or water.
• There are no shadows, no horizon or clouds and all depth-of-field and orientation are lost.
• A white out situation is severe in that there aren’t any visual references.
• Flying is not recommended in any white out situation.
• Flat light conditions can lead to a white out environment quite rapidly, and both atmospheric conditions are insidious: they sneak up on you as your visual references slowly begin to disappear.
• White out has been the cause of several aviation accidents in snow-covered areas

Self Induced White Out

• This effect typically occurs when a helicopter takes off or lands on a snow-covered area.
• The rotor down wash picks up particles and re-circulates them through the rotor system.
• The effect can vary in intensity depending upon the amount of light on the surface.
• This phenomenon can happen on the sunniest, brightest day with good contrast everywhere.
• However, when it happens, there can be a complete loss of visual clues.
• If the pilot has not prepared for this immediate loss of visibility, the results can be disastrous.

BLOWING PHENOMENA

• The Haboob was covered in the wind chapter
• Blowing dust, sand
• Winds need to be at least 15kts to pick up your common variety dust
• Settles out at the rate of 1,000ft/hour
• Usually 3,000 to 6,000 AGL but can extend upwards to 15,000

VOLCANIC ASH

VOLCANIC ASH

VOLCANIC ASH

VOLCANIC ASH

OBSCURATION

• Surface based phenomena
• Classified in 8ths and vertical visibility
• Restricted slant range vis
• Ceiling may be noted but once below it horizontal vis may be severely restricted

