A Guide To Aviation Weather Richard D. Clark, Ph.D. Professor of Meteorology Student Assistants: Keith Liddick and Sam DeAlba Department of Earth Sciences Millersville University 16 NOV 2005
Outline Icing Turbulence Wind Shear Precipitation Obscurations to Visibility Weather data and Research
Icing Rime Ice Conditions for formation: Rime Ice is a bumpy, grainy looking layer of ice formed by super cooled clouds of -10 C or cooler. Rime Ice on the wing of a plane.
Rime Ice Icing It is supercooled water freezing very quickly. It is lighter than other ice, but there is a danger in losing air foil due to bumps on the ice.
Icing Clear Ice (Glaze Ice) Clear Ice is transparent. Conditions for formation: Large droplet size. Super cooled rain with temperatures between 0 C C to -4 C. Although it is smooth, the main threat is it s weight on the wings.
Icing Profile
Icing Profile
Turbulence Light Turbulence occurs: Near hilly and mountainous areas. In and near convective clouds. In and near thermals, downbursts, microbursts In wind shears near: Troughs or lows aloft. Boundary layer interfaces (K-H) Jet Stream. Tropopause.
Turbulence Turbulent effects on plane for: Light turbulence Reported as light chop, turbulence, or CAT (Clear Air Turbulence). Effects on the aircraft: Slight erratic changes in altitude and/or attitude (pitch, roll, yaw). Light turbulence or CAT. Rhythmic bumpiness that does not effect altitude or attitude. Light chop.
Turbulence Moderate Turbulence occurs: In mountainous areas with winds of 25 to 50 kts. In/near dissipating thunderstorms. In/near towering cumuliform clouds. In strong thermals. In the lower 5,000 ft of the troposphere when sfc winds are 30 kts or more. In fronts aloft. In moderate wind shear.
Turbulence Turbulent effects on plane for: Moderate turbulence Reported as moderate chop, turbulence, or CAT. Effects on aircraft: Causes noticeable changes in altitude and/or attitude, but pilots are able to maintain control at all times. Moderate CAT or turbulence. Similar to light chop, but more intense. Moderate chop.
Turbulence Severe Turbulence occurs: In Mountainous areas with winds above 50 kts. In/near growing and mature thunderstorms. Sometimes in towering cumuliform clouds. In troughs aloft. On the cold (cyclonic) side of a jet stream. In lows aloft with strong wind shear.
Idealized Jet Streak
Jet Streak
Turbulence Turbulent effects on plane for: Severe turbulence Reported as severe turbulence or CAT. Effects on air craft: Causes large, abrupt changes in altitude and/or attitude. Large variations in airspeed are also noticeable. Aircraft is momentarily out of control.
Turbulence Extreme Turbulence occurs: In mountain wave situations where well-developed rotors are present. In/near severe thunderstorms. The video above shows mountain turbulence.
Turbulence Turbulent effects on plane for: Extreme Turbulence Reported as extreme turbulence or CAT. Aircraft is violently tossed about and practically impossible to control. Structural damage is very possible.
Extreme Turbulence Profiler and Sounding
Extreme Turbulence PiReps
Wind Shear Wind shear Is usually associated with turbulence. It can be found in winter-time time lows and summer-time highs. Can cause and unwanted loss or gain of airspeed.
Wind Shear Upper Flight Levels: Near jet stream. Near jet streaks. The tropopause. Probable Locations: Lower flight levels: Frontal zones. Thunderstorms. Temperature inversions. Nocturnal cooling. Ground obstructions.
Precipitation : Precipitation Any form of water particles, whether solid or liquid, that fall from the atmosphere and reach the ground (but watch for virga). Code RA DZ SN SG UP GR GS PL IC Meaning Rain Drizzle Snow Snow Grains Unknown Precipitation Hail (1/4 inch in diameter or larger) Small Hail/Snow Pellets Ice Pellets Ice Crystals
Precipitation Precipitation UP is used only by automatic weather reporting systems to indicate that the system cannot identify the precipitation with and degree of proficiency. This usually occurs when rain and snow are falling at the same time. GS is used to indicate hail less than ¼ inch in diameter. For IC to be reported, visibility must be reduced by the ice crystals to 6 SM or less.
Obscurations to Visibility Obscurations to Visibility : Any phenomena in the atmosphere, other than precipitation, that reduce horizontal visibility. Code FG BR FU HZ PY SA DU VA Meaning Fog (visibility less than 5/8 SM) Fog (visibility 5/8 to 6 SM) Smoke Haze Spray Sand Dust Volcanic Ash
Obscurations to Visibility: FOG Obscurations to Visibility Radiation Fog Cool surface air, small dew point depression. Advection Fog Warm, moisture-laden air moves over cool surface. Steam Fog Warm water, convection, condensation. Upslope Fog Adiabatic cooling of moist air.
Any Questions?