Weather #

Definitions:

• Squall: Sudden increase in strenght of wind for lunger duration than a gust
• Diurnal Variations: Nocturnal inversion develops when the sun sets and night falls. With no surface heating, turbulence dimishes
• Eddies: “Swirling” vortices caused by surface features of the earth (hills, mountains, valleys, trees, buildings, etc.)
• Veers: When wind changes direction clockwise
• Backs: When wind changes direction counter-clockwise
• Wind shear: The sudden “tearing” or “shearing” encountered along the edge of a zone in which there is a voilent change in wind speed or direction
• Jet stream: 3 sometimes 4 jet streams in north america, located between 20-40k feet. Move in an easterly direction
• CAT (Clear Air Turbulence): Occurs 15-30k feet. Severe turbulence that is created when contrasting cold and warm air masses meet. Random and transient, almost impossible to forecast. Most common is to avoid jet streams with strong winds at the core (150 knots)
• Condensation: Temp falls any lower after air is saturated, creates water droplets
• Deposition: Below freezing when saturation occurs, directly into ice crystals
• Sublimation: Visible water or ice crystals are heated, turn into invisible gas, water vapour. Therfore if fog or clouds are heated, they will disappear
• Visual Meteorological conditions (VMC): Indicate visibiility, distantance from cloud and ceiling are equal to or better than minima under which flight according to the VFR to be conducted.
• Instrument meteorological conditions (IMC): indicates visibility, distance from cloud and ceiling are below minima and flight can be conducted only under IFR.

Icing #

• Do not ever fly into icing conditions (especially clouds), unless your plane is equipped for it
• Occurs usually between 0c and -20c
• Temperature usually decreases -2c each 1,000 ft

ICAO Standard Atmosphere #

Important to memorize.

ICAO Standard Atmosphere assumes that:

• Air perfectly dry gas
• MSL pressure of 29.92 Hg
• MSL temperature of 15c
• Decrease of temeprature with height is 1.98c (round to 2) per 1,000ft
• Mercury drops 1 inch per 1,000ft increase

Calculating crosswind & headwind when landing #

Example:

• Wind 300 true at 12 kts gusting 19kts
• Wind 300 + 8 variation = 308 magnetic
• We round up or down to nearest number ending with zero = 310 magnetic
• Wind is 10 degrees off runway 30

After you know now it is 10 degrees off runway 30, you look at the chart to calculate that.

For example, see this:

Realistically, there is an easier / quicker way of calculating:

0-20degrees: 0% crosswind 20-40: 50% crosswind 40-50: 70% crosswind 50-70: 90% crosswind 70-90: 100% crosswind

If we use runway 23, winds 200, 14 knots wind speed:

1. Find difference: 230 - 200: 30
2. Convert difference: 30 difference becomes 30 degrees which would be a 50% crosswind.
3. Multiple percentage by wind speed: 7 knots

Mean Sea Level #

MSL at station A = Station pressure + Weight of the fictitious column of air between the station & mean sea level.

Isobars #

General:

• Drawn on a map with joining places having the same MSL pressure
• Drawn at four millibar intervals up and down starting at 1,000 millibars
• Lines never cross
• Form pressure patterns

How to read a map:

• Closely spaced isobars mean a steep pressure gradient and strong winds
• Widely spaced isobars mean a shallow pressure gradient and relatively light winds

Flying tips #

• High to low… look out below
• Low to high… only sky

Atmosphere #

• Troposphere: Lowest part of the atmosphere varies between 28k-54k ft depending on where near the equator. Most of where weather occurs due to presence of wayer vapour and strong vertical currents produced by the radiation of the sun
• Stratosphere: 50k ft depending on location. Water vapour almost non-existent, and air currents minimal
• Mesosphere: 275k ft Marked by decrease in temp that’s carried through. Most mteorites burn up here.
• Thermosphere
• Exosphere: Where pressure drops to little more than a vacuum

Standard Atmosphere #

Atmosphere being heated (CATS) #

• Convection: Air over warm surface rises, cooler air descends to take its place. Warm air rises as it is less dense than colder air surrounding it
• Advection: Horizontal movement of air by the wind. Cool air can become heated when it is blown over a warm surface
• Turbulence: Cause by friction between the air and ground creating eddies in an up and down motion
• Subsidence / Compression: Causes warm air to be pushed upward into the atmosphere

Atmosphere cooling (AREA): #

• Advection: Cause warm air mass to cool when it moves over cold surface
• Radiation cooling: At night, no longer receives solar radiation, however it continues to emit terrestrial radiation. Results in the cooling of the Earth’s surface
• Evaporation: State from liquid to a gas absorbs heat energy from the surrounding air, lowering its temperature
• Adiabatic Expansion: When atmospheric pressure surrounding a parcel of air decreases, parcel of air expands.

Latent heat #

• Point where a substance is ready to change state or phases without a corresponding temperature change
• Process of giving off or absorbing heat without changing temeprature is known as “latent heat transfer”
• Heat enegry that is “hidden” in water vapour
• For water vapour to evaporate, it must take heat away from the surrounding atmosphere
• Typically happens in the lower levels where terrestrial heat is absorbed
• If water vapour carrier to higher levels of atmosphere, eventually condense
• When it condenses, it releases the “hidden heat” and warm the surrounding air

Low & high pressure systems #

• Low pressure system: Counter clockwise (to remember… LEFT to RIGHT)
• High pressure: Clockwise

Inversions #

Day inversion #

• Exists when temperature of the air increases as altitude increases
• We can tell inversion exists as we can see the ‘pollution’ that is trapped beneath the warmer upper air
• Temp does not decrease at the standard rate

Night inversion #

Nocturnal inversions occur:

• When the earth cools the air above it leaving undistrubed warmer air aloft
• Warm air is forced aloft by descending cooler air

Clouds #

• Cumulus: Forms in rising air currents and evidence of unstable air conditions
• Stratus: Form in horizontal layers and usually form as layer of moist air cooled by its saturation point. Little turbulance in this.
• Nimbus: Clouds from which precipitation falls

Cloud formation #

• Result of air becoming saturated, causing water vapour to condense or sublimate when it encounters a neculi

• Air can become saturated by having its temperature lowered to the dew point or by having its dew point raises through the addition of water vapour

• Clouds can be cooled by convection, adiabatic expansion, advection and evaporation cooling

• Most cloud forms as result of aidabatic expansion due to rising air. When parcel of air rises, expands and cools latent heat exchange occurs

• If there is neucli present (dust, pollen, salt, etc.) the water vapour will condense onto it

High Clouds #

• Cirrus (Ci): Very high, thing wavy sprays of white cloud
• Cirrocumulus (Cc): Thin clouds, cotten flake-like. Gives little indication of future weather conditions
• Currostratus (Cs): Very thin high sheet cloud which the sun or moon is visible, producing halo effect. Freq. indication of approaching warm front or occlusion of deteriorating weather

Middle Clouds #

• Altocumulus (Ac): Layer patches rounded of cloud may lie in groups or lines. Indicate approach of a front, but usually they have little value of indication of future weather developments
• Altocumulus Castellanus (Acc): Altocumulus with a turreted appearance. Instability, turvulence and shower activity are characteristic
• Altostratus (As): Thick veil of grey cloud that generally covers the whole sky. Indicates near approach of warm front. Light rain or snow may fall from thick altostratus. icing may occur in this cloud.

Low Clouds #

• Stratus (St): Uniform layer of cloud resembling fog but not resting on ground. Drizzle often falls from stratus.
• Stratocumulus (Sc): Layer or series of patches of rounded masses or rolls of cloud. Very often thin with blue sky showing through peaks. COmmon in high pressure areas in winter and sometimes gives precipitation
• Nimbostratus (Ns); Low layer of uniform, dark grey cloud. When it gives precipitation, it is in the form of continuous rain or snow. Cloud may be more than 15,000ft thick.

Clouds of Vertical Development #

• Cumulus (Cu): Thick, rounded and lumpy representing cotton balls. Usually flat bases and the tops are rounded. Flight under these clouds usually bumpy
• Towering Cumulus (TCu): Cumulus clouds that build up into high towering bases. Rough air and heavy icing may occur in this cloud type.
• Cumulonimus (Cb): Heavy masses of cumulus clouds that extend well above freezing level. Summit often spread out to form an anvil shaped top that is characteristic of thunderstorm and showery conditions. Violent vertical currents exist within the cloud. Should be avoided due to its turvulence and heavy electrical / icing activity.

Determining Wind Speed #

Flight characteristics in stable vs unstable #

Frontal lifts #

• Mass of warm air advancing on colder mass, the warm air rises over the cold air on a slope. Warm frontal surface. Causes it to cool and clouds are formed, ranging from cirrus through altostratus to thick nimbostratus.

• Mass of cold air on a mass of warm air, cold air undercuts warm air and forces the warm to rise. Cold frontal surface. Clouds which form are heavy cumulus or cumulonimbus. Heavy rain, thunderstorms, turbulence and icing are associated with it.

Fronts #

• Warm front: Fast-ish moving. Pushes the “cold” air down / lots of rain / precipitation as the warm air “gets rid” of the cold air

• Cold front: Slower moving. If warm front has clouds, then possible thunderstorms. If stable / no clouds, then light precipitation.

• Stationary front: Sometimes there are parrallel winds and the fronts do not move

• Occluded front: When two cold airs “overtake” and “go around” and enclose warm air / warm front. The warm is is “pushed” up and out.

• Warm weather fronts generally are less pronounced than cold front changes and are very gradual. Weather at a warm front is usually more extensive and may cover thousands of square miles.

• The colder the air, the lower the tropopause
• Tropopause is higher hwn air is warm
• Coldest air mass lies at the lower level, the next coldest forms a shell over it and so forth until warmer air mass is reached
• Each air mass is normally topped by the Tropopause

Squall line #

A long line of squalls and thunderstorms is sometimes called a squall line. Usually associated with fast moving cold front that is undercutting an unstable arm air mass.

Cold Front Changes #

• Surface wind: Windshift may be quite abrupt

• Temperature: May drop sharply as front passes, but usually drops gradually

• Visibility: Usually improves after passage of cold front

• Pressure: Approach is accompanied by a decrease in pressure

• Turbulence: May be associated with cold front. Flight through will be rough.

• Precipitation: Usually narrow

• Pushed “under” the warm front

• Because of the vertical lifting, produces cumulus type clouds, better visibility, showery precipitation

• Cold front is narrow, changes happen rapidly and occur after the passage oft he front

• Steep frontal slope

• Clouds can occur about 50 miles ahead of the front

Passge of a cold front will result in the following:

• Winds will veer and may be gusty
• Temeprature drops
• Visiblity improves
• Precipitation is showery

Warm Front Changes #

• Wind: Wind will veer but a lot more gradual than cold front
• Temp: Gradual rise
• Visibility: Low ceiling and restricted visibility associated with warm fronts
• Turbulence: Cumulonimbus clouds frequently embedded in main cloud deck / these storms are responsible for severe turbulence.
• Precipitation: Usually starts between 8-12k feet.

• Usually a shallow frontal slope
• CLoud can extend more than 500nm
• Clous usually progress Ci, Cs, As, Ns.

Passage of warm front results in:

• Winds veer, but change gradual
• Temperature rises
• VIsiblity normally poor
• Precipitation will be continuous and may last for long periods

Pressures #

• Low pressure: Cyclones, depressions, lows: the air flows toward a low and is deflected to create a counterclockwise or cyclonic circulation

• High pressure: Deflected to the right and produces a clockwise circulation around an area of high pressure

• High pressure = good weather

• Low pressure = bad weather

Coriolis force #

• Air moving from a high pressure area to a low pressure area is deflected to the right in the Northern Hemisphere due to the criolis force, and as a result flows parallel to the isobars
• Southern hemisphere is goes left.

Convergence and Divergence #

• Convergence: flow of air into a region
• Divergence: flow of air out from a region

Mountain Wave #

• Lots of turbulence
• Wind shear varies dramatically
• Altimeter errors since increase in wind results in accompanying decrease in pressure
• Icing
• Vertical currents are very strong

Dewpoint #

• Basically, the air at which water vapour condenses into liquid.

• Smaller the spread between temperature and dewpoint, the more likelyhood for icing or cloud conditions to form.

• The temperature at which air must be cooled at constant pressure to become saturated is called the dewpoint.

• When the spread between temp and dewpoint is very small, air can be said to be nearly saturated and a slight drop in temp may cause condensation in the form of clouds, fog or precipitation.

• Fog or low clouds are likely to form when the temp is within 2c of the dewpoint

• Dewpoint is the temperature at a given pressure which air contains a given amount of moisture must be cooled to cause saturation

Adiabatic lapse rates #

• Dewpoint falls 0.5c per 1,000ft.
• Dry adiabatic lapse rate is considered to be 3c per 1,000ft (temp decreases)
• Saturated adiabatic lapse rate is considered to be 1.5c per 1,000ft (temp decreases)

Applying and understanding adiabatic lapse rate as you’ll be able to determine what altitude you might expect the bases of the clouds to be. You can also determine what altitude you might expect to encounter icing conditions.

Example:

• Surface temp is 15c, dewpoint is 5c. Surface elavation is 1,500ft. What height might the bases of the convective type clouds be expected to be?
• Temp in a rising column of unsaturated air decreases 3c per 1,00ft.
• Dewpoint is 0.5c per 1,000ft.
• In a rising column of unsaturated air, temp and dewpoint converge at a rate of about (3c - 0.5c) 2.5c per 1,000ft.
• The spread between dewpoint and temp is 10 (15 - 5).
• 10 / 2.5 is 4.
• Therefore the bases of the clouds can be expected to be at a height of approx 4,000ft AGL or 5,500ft ASL. The dewpoint at this altitude would be 3c.

Quicker method would be to calculate the bases of cumulus clouds is determine the spread between temp and dewpoint and multiply by 400.

Icing conditions:

• At what height might icing conditions be encountered?
• Saturated rising air, lapse rate averages about 1.5c per 1,000ft.
• Base of the cloud is at 5,500ft ASL at temp of 3c.
• Spread between dewpoint and freezing is 3c.
• 3 / 1.5 is 2.
• The freezing level would therefore be expected at 2,000ft above the bases of the clouds, or 7,500 ASL.

Relative humidity #

Ratio of the actual water vapour present in the air to the amount which the same volume of air would hold if it was saturated.

• Saturated air has 100% relative humidity
• Dry air has 0% relative humidity

When a given mass of air is heated and no new water vapour is added, the humidty of air decreases.

If it is cooled, the relative humidity increases.

DRY Adiabatic Lapse Rate (DALR) #

• Rate at which air cools as it rises due to expansion when the air is NOT saturated
• Air cools at 3c per 1000ft
• Then temp of air reaches dew point, air becomes saturated and cloud or fog form
• Dew point remains constant & does not change with height

SATURATED Adiabatic Lapse Rate (SALR) #

• Rate at which air cools as it rises due to expansion when the air IS saturated.
• As saturated air cools, water vapour condenses, changing from a vapour to a liquid
• Change of state releases latent heat to the air warming it & decreasing the lapse rate to 1.5c / 1000ft.
• As moisture is removed from the air by condensation, the dew point decreases with temperature.

Environmental Lapse Rate (ELR) #

• ELR is the actual lapse rate of the air surrounding the parcel of air which is rising
• Surrounding air must be cooler than the parcel of air else it would not rise

Absolute humidity #

• Expresses the weight of water vapour per unit volume of air. Usually in grains of water vapour per cubic foot of air

Density / Temperature #

• Warm air is less dense because molecules which compose it move about rapidly.
• Cold air is more dense because molecules move more slowly.

Lifting agents of air #

• Convection: Air heated through contact with earth’s surface
• Orographic lift: Air moving up in sloping terrain (mountainside)
• Frontal lift: When different air masses meet, warm air is forced aloft by advancing wedge of cold air
• Mechanical Turbulance: Friction between the air and ground disrupts the lower levels of air into a series of eddies
• Convergence: In low pressure area, the winds blow across the isobars into the centre of the low. Air accumulates in the center of the low and excess air forced to rise.

Masses of air #

• Continental Arctic / Continental Polar: Cold dry air masses which originate over the intesely cold ice and snow surface
• Maritime Arctic / Maritime Polar: Cold air masses form over the Arctic and acquire moisture as they move south over the cold waters of the North Atlanctic and North Pacific oceans
• Maritime Tropical: Because the continent of NA narrows down towards southern part, most of the tropical air focuses on the coast towards Mexico, SA.

METAR #

CYQG 171942Z 27019G27KT 9SM BKN023 BKN028 OVC034 03/M01 A2957 RMK SLP020:

• Station Identifier: CYQG

• Date and Time of Report: 171942Z (17th day of the month at 19:42 UTC)

• Wind: 270 degrees at 19 knots, gusting to 27 knots (27019G27KT)

• Visibility: 9 statute miles (9SM)

• Sky Conditions: Broken clouds at 2,300 feet above ground level (BKN023), broken clouds at 2,800 feet above ground level (BKN028), and overcast clouds at 3,400 feet above ground level (OVC034)

• Temperature and Dew Point: 3 degrees Celsius, with a dew point of -1 degree Celsius (03/M01)

• Altimeter Setting: 29.57 inches of mercury (A2957)

• Remarks: Sea Level Pressure is 1,020 hectopascals (SLP020)

• 060V130: Wind varying between 60 to 130 degrees

• 1/2SM: indicated prevailing visibility of 1/2 a statute mile

Present weather:

• VC used for vicinity
• Intensity is: (-) light, (no sign) moderate, (+) heavy.
• DS: Duststorm
• SS: Sandstorm
• FG: Fog
• SH: Shower
• PO: Dust or Sand Swirls
• BLDU: Blowing dust
• BLDSA: Blowing sand
• BLSN: Blowing snow
• FC: Funnel Clouds (Tornado / waterspout)

Descriptor:

• MI: Shallow
• BC: Patches
• DR: Drifting
• BL: Blowing
• SH: Shower
• TS: Thunderstorm
• PR: Partial
• FZ: Freezing

Weather phenomena:

• DZ: Drizzle
• RA: Rain
• SN: Snow
• SG: Snow grains
• PL: Ice pellets
• GR: Hail
• GS: Snow pellets
• IC: Ice crystals

Obscuration:

• HZ: Haze
• FU: Smoke
• SA: Sand
• DU: Dust
• FG: Fog
• BR: Mist
• VA: Volanic ash

Sky condition:

• CLR: Clear
• SKC: Sky clear
• FEW: Few clouds
• SCT: Scattered
• BKN: Broken
• OVC: Overcast

Obscured sky: VV is used. Example: VV010 is sky obscured @ 1k feet.

Temperature and dew point: By two digit groups and a slash.

Example: 15/10 indicates air temp of 15c, and dewpoint of 10c.

M indicates minus, example: M05/M10

Altimeter:

• 4 digits by the letter A. Example: A2992 is altimeter 29.92inches
• For hecopascals it’s Q. Example: Q1013 = 1030 hectopascals

Wind shear:

• WS RWY18: Windshear encountered on runway 18
• WS ALL RWY: All runways

Remarks:

• RMK indentifies information on cloud type and layer opacity (in oktas), seal level pressure (SLP) in hectopascals and any other signifiant information
• RMK SC3 CI0 SLP134 indicates 3/8 opacity of stratocumulus, 0 opacity of cirrus and sea level pressure of 1013.4 hPa.

METAR Sky Condition #

METAR reporting weather code is divided into 8 segments called oktas, sky conditions are:

• Clear: No clouds
• Few: 2 oktas or less of celestial dome covered by clouds
• Scattered: 3-4 oktas
• Broken: 5-7 oktas
• Overcast: 8 oktas

PIREP - Pilot Reports (PREP UUA/UA) #

KCMH UA /OV APE 230010/TM 1516/FL085/TP BE20/SK BKN065/WX FV03SM HZ FU/TA 20/TB LGT:

• KCMH - Closest weather reporting airport (Columbus Ohio)
• UA - Routine PIREP
• /OV APE 230010 - location one zero miles southwest of Appleton VOR
• /TM 1516 - time 1516 UTC
• /FL085 - altitude eight thousand five hundred
• /TP BE20 - aircraft type Beech 200 Super King Air
• /SK BKN065 - base of the broken cloud layer is six thousand five hundred
• /WX FV03SM HZ FU - flight visibility 3 miles with haze and smoke
• /TA 20 - air temperature 20 degrees Celsius
• /TB LGT - light turbulence

Notes:

• 01: Urgent
• 10: Normal

Aerodrome Forecast (TAF) #

• Report name
• Wind (35020G45KT)
• Low level wind shear (WS 015/20015KT)
• Prevailing visibility (3/4SM)
• Significant forecast weather (-RA BR TEMPO RA BR)
• Sky condition (SCT008 BKN015CB BKN250)
• Forecast change and time (24010KT P6SM SKC FM 091640 27015KT P6SM SKC)

Upper winds and temperature forecast #

Provides an estimate of upper wind conditions and temperatures at selected levels. Given in degrees true + wind.

Above example: For YVR @ 600ft it’s wind at 240 at 25knots with temperature at minus -07.

• Reads 9900 when winds less than 5kts. Meaning light and variable.

Reporting services #

• Aviation Weather Briefing Service (AWBS): 1-866-WX-BRIEF
• DUATS: Direct User Access Terminal System
• Pilot Automatic Telephone Weather Answering Service (PATWAS): Public telephone access
• AIRMET (WA): Aircraft in flight to notify pilots of potentially hazard weather conditions not requiring a SIGMET
• Environment Canada Bulletin Board Service: Bulleting board service to provide up to date information in a menu like service
• Internet: navcanada.ca
• PIREP: Pilot reports by pilots in flight of any unusual weather conditions

Wind #

• Relative wind is simply the wind that’s relative to you when you move (example, a flag ontop of a car that’s moving)
• Wind has zero effect of lift. Head wind or tail wind wont affect your actual lift..

Directions #

• Behind you = makes you moov faster
• Side = crab-like gait
• Front = slows you down, lose speed

Three aspects #

• Air is a soup / thick and in in constant motion
• Motion is relative
• You’re in the air: like walking through a moving train

Rough air / turbulance #

• Disturbance isn’t caused by change of air speed or weight, but a change in angle of attack. Example: flying into an updraft

Dealing with crosswind #

• Most of the time you side slip, other times you crab (major airliners, don’t have much wingtip room to do so..)

Wind Shear #

Sudden change of wind direction:

• A sudden LOSS of headwind will decrease performance shear. DECREASED airspeed = less lift
• A sudden INCREASE in headwind will result in an increased performance shear. INCREASED airspeed = more lift

Turbulence #

• Convective: Convection causes by alternatinv rising and sinking verticle columns of air. As is results from daytime heating, it will quickly dissipate after sunset. Above the convective cloud, the air is smooth.

• Mechanical: Caused when air is disturbed by surface friction or obstructions = Unstable air, rough terrain, and strong winds result in severe turbulence.

• Orographic: Caused by large obstaces like mountains, features, etc. May also result in formation of mountain wave.

• Wind Shear: Large changes in the *direction or speed of wind that can occur over short distances or heights.

• Reporting criteria: Light turbulence, light chop (rhythmic bumpiness), moderate turbulence, moderate chop, severe turbulence, extreme turbulence

Clean aircraft concept #

• Critical surfaces, include the wings, control surfaces, propellers, and horizontal and vertical stabilizers
• On the leading edge and upper surface of a wing, ice can reduce wing lift by as much as 30% and increase drag by 40%.

Turbulence #

• Convective: Convection causes by alternatinv rising and sinking verticle columns of air. As is results from daytime heating, it will quickly dissipate after sunset. Above the convective cloud, the air is smooth.
• Mechanical: Caused when air is disturbed by surface friction or obstructions = Unstable air, rough terrain, and strong winds result in severe turbulence.
• Orographic: Caused by large obstaces like mountains, features, etc. May also result in formation of mountain wave.
• Wind Shear: Large changes in the *direction or speed of wind that can occur over short distances or heights.
• Reporting criteria: Light turbulence, light chop (rhythmic bumpiness), moderate turbulence, moderate chop, severe turbulence, extreme turbulence

Thunderstorms #

• T with a warm front usually have stratus clouds.
• T with a cold front are more severe because of the rate of lifting.
• Air mass T’s form within a warm, moist air mass, are in no way associate with fronts
• Generally isolated or widely scattered over a large area

Air mass t’s may be classified as:

• Convective:

Normally due to heating from below in a moist, unstable, slow moving air mass.

• Orographic

Caused by orographic lift, normally obscrubed by stratus cloud on windward side.

• Nocturnal

Found in air mass in the mid-west. Occurs at night or early in morning in the central plains. Unusually moist air aloft. Trigger action initiating these storms is thought to be night-time radiation from this moist air layer.

On the leading edge and upper surface of a wing, can reduce wing lift by as much as 30% and increase drag by 40%.