Weather Hazards

Chapter 9, Section B

Thunderstorms

• Conditions– Unstable air

– Lifting action

– High moisture content

• Stages– Cumulus stage Mature stage

– Dissipating stage

Hazards

• Embedded thunderstorms may be obscured by cloud layers

• Wind shear can be found on all sides as well as directly under it

• Greatest intensity during mature stage, which is signaled by precipitation at the surface

Types of Thunderstorms

• Airmass thunderstorms are usually isolated or scattered over a large area

• Frontal thunderstorms associated with frontal activity

• Squall line is a narrow band of active thunderstorms normally containing severe weather

Hazards

• Lightning is always associated with thunderstorms

• Hail is often associated with cumulonimbus clouds but can be found in clear area several miles from the cloud

• Funnel clouds - tornado or waterspout

Thunderstorm Avoidance

• Use weather radar to avoid thunderstorms

• Avoid echoes by at least 20 miles - Do not fly between if less than 40 miles apart

• Weather radar does not pick up fog or clouds

Turbulence

• Low-level Turbulence below 15,000 feet consists of– Mechanical Turbulence

– Convective Turbulence

– Frontal Turbulence

– Wake Turbulence

Mechanical Turbulence

• Wind forms eddies as it blows around hanger, stands of trees or other obstructions

Convective Turbulence

• Thermal Turbulence is a daytime phenomena which occurs over land in fair weather

• Capping stable layer begins at the top of the convective layer. It can be identified by a layer of cumulus clouds, haze or dust

Frontal Turbulence

• Occurs in the narrow zone just ahead of a fast-moving cold front

Wake Turbulence

• Wingtip vortices occurs when an airplane generates lift

• They can exceed the roll rate of an aircraft

• Greatest when an aircraft is heavy, slow and clean

Wingtip Vortices

• Tend to sink below the flight path of the generating aircraft

• Most hazardous during light, quartering tailwinds

• Land beyond where a large aircraft has touched down

Wingtip Vortices

• Lift off before the point a large aircraft departing in from of you lifted off climb out above his flight path or turn upwind

• Helicopters in forward flight produce wingtip vortices like circulation of air

Clear Air Turbulence

• Turbulence above 15,000 feet AGL not associated with cumuliform cloudiness is reported as CAT

• CAT is common in a upper trough on the polar side of the jet stream

Jet Stream

• A curving jet stream associated with a deep low pressure trough can be expected to cause great turbulence

• Jet stream can sometime be identified by long streaks of cirrus clouds

Mountain Wave Turbulence

• Greatest turbulence occurs approaching the lee side of a mountain range in strong headwinds

• Standing lenticular and rotor clouds indicate the possibility of strong turbulence

Reporting Turbulence

• Light - slight erratic changes in altitude or attitude

• Moderate - aircraft remains in positive control

• Severe - large abrupt changes in altitude and attitude and may be momentarily out of control

Wind Shear

• Sudden, drastic shift in wind speed and/or direction over a short distance

• May be associated with a strong low-level temperature inversion, a jet stream, a thunderstorm or a frontal zone

Microbursts

• Intense, localized downdrafts seldom lasting longer than 15 minutes

• Downdrafts can be as strong as 6,000 feet per minute

• Performance changes drastically as an aircraft flies through a microburst

Low-Level Wind Shear Systems

• LLWAS - system of anemometers compares wind speed at several locations around the airport

• Terminal Doppler Weather Radar provide a clearer, more detailed picture of a thunderstorm

• Visual - Virga

Restrictions to Visibility

• Fog, haze, smoke, smog and dust

• Fog requires moisture and condensation nuclei

• Industrial areas produce much fog since they have more condensation nuclei

Fog

• Radiation Fog - ground fog - forms over fairly flat land on clear, calm nights

• Advection fog- forms near coastal areas when moist air moves over colder ground or water

Fog• Upslope fog forms when moist stable air

is forced up a sloping land mass• Steam fog occurs as cool air moves over

warmer water• Precipitation-induced fog forms when

warm rain falls through a layer of cooler air near the surface

Fog

• Ice fog occurs in cold weather when the temperature is much below freezing and water vapor sublimates directly as ice crystals

Icing

• Freezing rain is most likely to have the highest rate of accumulation

• Ice, snow or frost having the thickness and roughness of sandpaper and reduce lift by 30% and increase drag by 40%

Cold Weather Operations

• Preheat the cabin as well as the engine, but not at KSU

• Warm crankcase breather lines since they may be clogged by ice from vapors that have condensed and subsequently frozen

338. I27 COM

Fog produced by frontal activity is a result of saturation due to

A. evaporation of precipitation.

B. adiabatic cooling.

C. nocturnal cooling.

338. I27 COM

Fog produced by frontal activity is a result of saturation due to

A. evaporation of precipitation.

363. I31 COM

A situation most conducive to the formation of advection fog is

A. a light breeze moving colder air over a water surface.

B. an air mass moving inland from the coastline during the winter.

C. a warm, moist air mass settling over a cool surface under no-wind conditions.

363. I31 COM

A situation most conducive to the formation of advection fog is

B. an air mass moving inland from the coastline during the winter.

364. I31 COM

Advection fog has drifted over a coastal airport during the day. What may tend to dissipate or lift this fog into low stratus clouds?

A. Wind 15 knots or stronger.

B. Nighttime cooling.

C. Surface radiation.

364. I31 COM

Advection fog has drifted over a coastal airport during the day. What may tend to dissipate or lift this fog into low stratus clouds?

A. Wind 15 knots or stronger.

365. I31 COM

In what ways do advection fog, radiation fog, and steam fog differ in their formation or location?

A. Steam fog forms from moist air moving over a colder surface; advection fog requires cold air over a warmer surface; radiation fog is produced by radiational cooling of the ground.

B. Advection fog deepens as windspeed increases up to 20 knots; steam fog requires calm or very light wind; radiation fog forms when the ground or water cools the air by radiation.

C. Radiation fog is restricted to land areas; advection fog is most common along coastal areas; steam fog forms over a water surface.

365. I31 COM

In what ways do advection fog, radiation fog, and steam fog differ in their formation or location?

C. Radiation fog is restricted to land areas; advection fog is most common along coastal areas; steam fog forms over a water surface.

366. I31 COM

With respect to advection fog, which statement is true?

A. It can appear suddenly during day or night, and it is more persistent than radiation fog.

B. It forms almost exclusively at night or near daybreak.

C. It is slow to develop, and dissipates quite rapidly.

366. I31 COM

With respect to advection fog, which statement is true?

A. It can appear suddenly during day or night, and it is more persistent than radiation fog.