Frontal cloud and precipitation patterns of most fronts are not recognizable above 15,000 feet. However, temperature and pressure gradients often extend into the troposphere. Winds usually shift 90° from one side of the front to the other. Speeds of warm fronts are usually 15 knots, and cold fronts move about 20 knots.

The polar front is the zone separating the warm tropical air masses and the cold polar air masses.

The four major properties that distinguish a front are the changing temperature, varying dew points, wind shifts and pressure gradients.

The five major factors that influence weather are the slope of the front, the spread of the frontal movement, the degree of stability of the lifted air, the amount of moisture available, and the temperature and moisture gradient.

A cold front is the leading edge of an advancing cold air mass. A cold front overtakes and uplifts the warm air mass creating violent unstable conditions, cumulonimbus clouds, thunderstorms and severe turbulence. Ahead of the front, the SW winds increase, the barometric pressure decreases and altocumulus clouds appear on the horizon. The cumulonimbus clouds move in and develop rain or snow showers, increasing in intensity as the front approaches. As the front passes, the pressure rises sharply, the wind shifts to the NE and the clouds clear rapidly. The temperature and the dew point decrease, and colder drier weather begins. Cold fronts generally move southeast at 20 knots.

A squall line is a nonfrontal line of violent thunderstorms. They usually develop 50 to 300 miles ahead of the cold front and run parallel to it. Squalls contain severe weather conditions such as thunderstorms, heavy rain, lighting, icing, heavy turbulence and hail or tornadoes. Squall lines are considered to be frontal weather.

A warm front is the leading edge of the advancing warm air mass that is overtaking and replacing a colder air mass. A warm front typically moves slower (15 knots) in a NE direction and tends to glide over the top of the colder air. The front is gradual and characterized by a sequence of clouds, beginning with cirrus, cirrostratus, then altostratus, nimbostratus, and then the low-lying stratus, with rain and fog. With the passage of a warm front, the winds change from the SE to the SW, and are followed by an increase of pressure and temperature.

A front that has no movement from one air mass toward the other. It is characterized by a pressure gradient and by a 180° shift in winds. The weather patterns of a stationary front are often very similar to the weather patterns of a warm front, but are usually less intense.

Occluded fronts occur when three fronts meet. It occurs when a cold front overtakes a warm front that is behind a cold front. The type of occlusion that develops depends on which front remains in contact with the earth. Occluded fronts generally align themselves to the north and south and move to the northeast at the speed of the front that is near the earth. The weather associated with the occlusion will be a combination of both types of frontal-weather. A cold front is an occlusion where the colder of the two cold fronts is the one overtaking the warm front. A warm front occlusion is an occlusion where the warmer of the two cold fronts is overtaking the warm front, and rising over the other cold front.

An upper front is a cold front aloft that moves over an even colder air lying in the lower layers of the atmosphere.

Inactive fronts do not create clouds or precipitation. This occurs when the fronts are too dry to form clouds. The front only has a shift in wind direction and pressure.

Lifting action, unstable air, high moisture content, and a cloud building through the freezing level.

Extreme turbulence, hail, microbursts, icing, lightning, and tornadoes.

A microburst is an intense highly localized downward atmospheric flow that emanates from a convective cloud, usually in the mid-afternoon of summer months.

Microbursts usually begin at the base of a cloud and spread out to areas over a two-mile expanse. They usually last 5 to 10 minutes and may develop in groups. The winds can be as low as 20 knots or exceed 200 knots. They may create vortex rings, or swirling areas of winds along the ground. Dry microbursts may occur under higher clouds that are providing no precipitation. High wind shear is associated with these phenomena.

An intense rotating column of air that protrudes from a cumulonimbus cloud in the shape of a funnel, rotating over the earth’s surface for anywhere from a few feet to hundreds of miles, travelling from 25 to 40 mph. Tornadoes are a little known about phenomenon and are very destructive. To form, they must have warm moist air near the earth’s surface, cold and dry air in the middle of the atmosphere, strong upper level winds, and the presence of Cumulonimbus clouds. The possible indications for the onset of a tornado are pronounced wind shear, rapidly moving cold front or squall line, strong convergence, marked convective instability, an abrupt change in moisture content and marked convection.

Radar can help to detect thunderstorm activity by bouncing radar waves off of the down falling precipitation to measure intensity.

Avoid them if possible and do not venture closer than 20 miles of mature storm clouds or anvils. If not possible, attempt to fly around the storm. If not possible, try to fly over the top, If not possible fly below the storm. If not possible fly through the lower 1/3 of the storm.

Vertical air movements resulting from convective currents develop in air that is heated by contact with a warm surface. This heating from below occurs when either cold air is moved over a warmer surface, or the ground is strongly heated by solar radiation.

The upper limits of the convective currents are often marked by haze lines or by the tops of cumulus clouds that form when the air is moist.

Movement of wind over an obstacle creates wakes or eddies on either side of the obstacle that can extend for miles beyond the surface that caused the turbulence.

When the air is stable, large waves form on the lee side of the mountain peaks and extend up into the stratosphere for up to 100 miles and downwind for up to 150 miles. Mountain wave turbulence is caused by the oscillation of the wind as it tries to return to the level that it was before it was lifted. Rotor clouds form at a lower level and are generally found at the same height as the mountain ridge. The cap cloud obscures both sides of the mountain peak. The lenticular clouds are stationary and above the height of the mountaintop.

Frontal turbulence is caused by lifting of warm air by a frontal surface leading to instability and/or wind shear between the warm and cold air masses.

Turbulent wind shear flight conditions are frequently found in the vicinity of the jet stream where large shears in both the horizontal and vertical planes are found as well as in association with land and sea breezes, fronts, inversions and thunderstorms.

Choose a cruising altitude away from the jet stream, avoid areas of rapidly shifting wind direction, and observe pilot and weather reports prior to flight.

It increases weight and drag, decreases lift and thrust and decreases performance. It disrupts the smooth flow of air over airfoils, decreasing lift and thrust and increasing drag and stall speed.

Liquid found at air temperatures below freezing. Usually found in clouds between 0 ° C an –15 ° C.

Climb to colder temperatures until encountering dry snow or descend to an altitude where temperatures are well above freezing.

Outside air temperature below freezing, aircraft skin temperature below freezing and visible moisture.

0 ° C or colder. The most sever icing is encountered between 0 ° C and -10 ° C.

The size and number of water drops in a given volume of air, airfoil thickness, and airspeed. Larger airfoils, smaller drops and decreased airspeed reduce accumulation.

Deicing Boots and rubber bladders are installed on the leading edges of lift producing surfaces. They inflate/deflate in cycles, allowing ice to crack and peel off into the air stream. Anti-icing fluids are pumped through holes in the wing’s leading edge. Ground crews also use de-icing fluids.

Frozen precipitation or frost, wet aircraft coming out of hangers, water or slush splashed onto the aircraft, and ice or snow on the runways.

Pilot reports are necessary because weather personnel often can not observe icing.

Any collection of particles, such as haze, fog and smoke which reduce horizontal visibility to less than seven miles.

If the sky is totally hidden from view by a surface based phenomenon, the reported ceiling is determined by the vertical visibility upward as seen from the ground. When surface based obscuring phenomena present a slant range visibility problem they may also be classified as a ceiling.

Fog is a visible mix of small water particles that resides within 50 feet of the surface, is greater than 20 feet in depth and reduces vertical and horizontal visibility to less than 5/8 of a statute mile.

The horizontal motion of air next to the earth’s surface produces friction; friction causes the air near the ground to tumble, resulting in eddy currents. These currents mix the air sufficiently to cause a layer of air near the ground to reach a saturated state and produce fog or low clouds.