Bumping along

Reference AIM MET 3.7 Turbulence Reporting Criteria

Intensity:

• light
• turbulence: momentary, slight changes in altitude/attitude
• chop: slight, rapid, rhythmic bumpiness without appreciable changes in altitude/attitude
• moderate
• turbulence: greater than light, aircraft remains in positive control, variations in IAS
• chop: greater than light, rapid bumps/jolts without appreciable changes in aircraft altitude/attitude
• severe
• large, abrupt changes in altitude/attitude
• large variations in IAS
• momentary loss of control

Frequency:

• occasional (<1/3 of the time)
• intermittent
• continuous (>2/3 of the time)

Report:

• location
• time
• intensity
• in or near cloud
• altitude
• type of aircraft
• duration (if applicable)

High level turbulence not associated with cumuliform clouds should be reported as CAT.

Wind

Reference ACWM Chapters 5 and 11

Wind is the result of changes in pressure gradient.

• flows from High to Low 
• steeper gradient = stronger wind

Coriolis Effect

• the deflection of wind caused by the Earth's rotation
• varies from zero at equator to maximum strength at poles

Curvature Effect

• when isobars are curved, air moves in an arc >> centrifugal force
• the pressure gradient around lows is generally stronger than around highs

Friction

• As you climb from the surface to 3000 feet, the wind veers (clockwise change in direction) and increases.
• As you descend from 3000 feet to the surface, the wind backs (counterclockwise change in direction) and decreases.
• We must also keep in mind that land and water create different amounts of friction.  There is less friction over water, so wind would blow at less of an angle across isobars and at faster speeds. 

Squalls and Gusts

• characteristics of turbulent flight conditions
• Gusts >> rapid peaks and lulls
• Squalls >> sudden increase lasting for a minute or more, then a decrease

Diurnal Effects

• surface winds are usually stronger and gustier during the day
• Sea Breeze during the day (higher pressure over water than land)
• Land Breeze at night

Topographical Effects

• hilly and mountainous terrain can contribute to mechanical turbulence
• Anabatic winds flow upslope during the day when mountain slops facing the sun are heated
• Katabatic winds flow downslope
• warm = Chinook wind, warms at DALR
• cold = glacier wind, cooling by underlying ice

Wind Shear

• increased performance (headwind) >> airspeed increases
• encountering increased performance on glideslope >> would have to reduce power to recapture glidepath, then increase power to maintain due to stronger headwind
• decreased performance (tailwind) >> airspeed decreases

Practical Meteorology

Practical Meteorology is all about applying all that meteorological theory to actual weather observations and forecasts.  There were a couple things I'd forgotten.   For example, with cloud layers, anything with 5/8 (broken) coverage or greater constitutes a ceiling.  This is not true if the it is a surface based layer, such as fog or snow.  In this case, the coverage must bee 8/8 to be considered a ceiling.  

Also, there are some charts that I don't use on a daily basis, because they cover much larger areas than I need on my regular runs between Montreal and Toronto.  When doing my practice questions, I was getting questions with regards to issuing and validity times wrong, so I knew it was time to consult the AIM.  

Prognosis = Forecast
Analysis = Observation

Reference AIM MET 3.2.1 Aviation Forecasts and Charts

Significant Weather Forecast - PROG Chart

• prepared 4 times daily, based on 00Z and 12Z data
• issued 12 hours prior to validity time (00, 06, 12, 18Z)
• specific flight level range (i.e. 700 - 400 MB = FL100 - FL240; also FL250-630)
• indicate surface positions of lows, highs, and any significant weather (thunderstorms, turbulence, mountain waves, etc)
• a forecast area of turbulence implies a 50% probability of encountering turbulence somewhere within the depicted area
• jet streams are depicted when the core speed is forecast to attain 80 knots or more

Upper Level Forecast - PROG Chart

• issued 4 times daily, 12 hours before the validity times of 00, 06, 12, 18Z
• applicable FL240, FL340, FL390, FL450
• depicts forecast wind and temperatures for the chart level

Reference AIM MET 3.2.3 Weather Charts

Surface Weather Chart

• observed at 00, 06, 12, 18Z
• issued 2-3 hours after observation
• pressure patterns from surface up to 3000 ft
• surface location of fronts, precipitation, obstructions to vision

Upper Level Chart - ANAL

• observed at 00 and 12Z
• issued over 3 hours after observation
• show reported atmospheric conditions at the pressure levels, such as wind speed/direction, temperatures, moisture content
• the contours or altitude gradient can be considered as the slope of the pressure surface