Weather and pressure (density vs true altitude), Cloud base, freezing level, DALR, SALR, Surface heating

How to calculate Pressure Altitude
Ref: https://www.youtube.com/watch?v=KcisGhtIigE

Pressure Altitude definition:
The height above the standard datum plane. (Sea level, 15 degrees, 29.92 in mercury, 1.98 degrees per 1000 ft, 14.7)

Pressure Altitude Method 1:
Set altimeter to 29.92 and read pressure
Pressure altitude Method 2:
((29.92 - altimeter setting) * 1000)
add this to:
    Field elevation if you're trying to get PA on ground
    Flight elevation (set to altimeter setting?) if you're trying to get PA in air
Pressure altitude Method 3: (no need to memorize)
    hAlt = (1-(pSta/1013.25)^0.190284) x 145366.45

True altitude:
Setting the altimeter to altimeter setting approximates True altitude (actual altitude above sea level)

Trough: a line that juts out from a low pressure area

Ridge: Similar to trough but on a high pressure area, typically nice weather

Col: area between two low and two high pressure areas creating unstable weather. Fog in wintertime, showers and thunderstorms in the summer.

Heat an area of air up and the molecules will expand, this pushes air upward.  You would get higher pressure if the air was not able to expand upwards but due to expansion the pressure on the ground may not change with heat.  Higher temperatures means fewer molecules to bite, fewer for the air intake so worse takeoff properties.  So:

High temp = Poorer density altitude = worse takeoff properties.

Also high temps mean ASL (density alt) is higher than true altitude.  Low temps mean ASL (density alt) is lower than true altitude.

Heat in the atmosphere is moved around by:
Convection
    Upwards movement of heat (a thermal)
Advection
    Sideways movement of heat (like over lakes)
Conduction
    Heat from the sun is absorbed by the earth and then released by the earth.
Latent heat
    When things cool down (water) the heat gets released, often due to air rising.  Air cools as it expands
Compression
    Air warms up when compressed
Turbulent Mixing
    Flowing air gets randomly blocked (by buildings, trees, etc) and becomes turbulent.

Processes for cooling the atmosphere:
Radiation
    Infrared radiation goes out into space, unless there is cloud cover to slow it.
Advection
    A snow covered field, cold air moves to where warm air is and cools
Adiabatic cooling
    Rising air expands, which causes air to cool. Air forced up a mountain slope is an example.

Dry Adiabatic Rate (this is not dry air, it's air where we can not see the water vapour). It's 3º per 1000º ft.
Saturated Lapse Rate (when you can see the moisture in the air). It's 1.5º per 1000 ft
Environmental Lapse Rate is 2º per 1000 ft (technically not a constant value and changes with inversions, etc)

When calculating cloud base you use 3º - .5º (2.5º) per 1000 ft until the dew point, then you use 1.5º per 1000 to get cloud height. the -.5º is the effect of the dew point falling as altitude increases. Latent heat is being released causing this difference.

Cloud base example (for cumulus cloud type only)
Surface temp 10º, dew point 5º
1000 * (temp - dewpoint) / 2.5 = cloud base in AGL
1000 * (10 - 5) / 2.5 = 2000 ft AGL is the base of our cloud.

If 10º air becomes saturated at 6,000 ft then what is the temp at 10,000 and 4,000 ft?
    Weirdly this question expects you to assume the 10º air is at the saturation level of 6,000 ft, not at sea level.  So:
    (6,000 - 4,000) /1000 * 3 = 6º hotter at 4,000 so 10º+6 = 16º @ 4,000 ft.
    (10,000 - 6,000)/1000 * 1.5º = 6º colder at 10,000 so 10º - 6º = 4º @ 10,000 ft.

Cloud base / freezing level example (cumulus cloud type only)
Elevation 900 ft
Temp 24º at surface
Dewpoint 15º
Steps: Figure out Cloud base with 2.5º per 1000, then freezing level (0º) at 1.5º per 1000:
((24-15) / 2.5 * 1000 )+ 900 = 4,500 - cloud base
Since the dewpoint reduces by .5 per 1000 ft we have to calculate a new dew point for 3,600ft
15º - (.5 * (3600 / 1000)) = 13.2º dewpoint at 4,500
(13.2º / 1.5º * 1000) + 4,500 = 13,300- freezing level

Moisture Presentation - Slide 25

Moisture Presentation - Slide 28

For the TC exam if they state cumulus clouds then 2.5 is used as it gives a higher base, which is shown in the presentation. If stratus clouds or no cloud type is mentioned then use the 3 degrees. Since the question refers to a cloud type of stratus,

15 / 3 = 5 x 1 000 = 5 000 feet AGL this is showing getting the cloud base of the stratus clouds
5 000 / 1 000 x 0.5 = 2.5 here is finding the correction to get the new dew point (every 1 000 feet the dew point drops 0.5C)
(3 - 2.5) / 1.5 = 0.333 x 1 000 = 333 feet + 5 000 feet AGL = 5 333 feet AGL this is finding the freezing level using the new dew point (dew point - correction)
5 333 + 523 feet ASL = 5 856 feet ASL this is converting from AGL to ASL

The correct answer is: 5 856 feet ASL.

For WWFC:
Use 2.5º(SALR-.5) per 1000 to the base and then 1.5º(DALR) per thousand to 0º for the tops.

Windward side of mountain (wind is from this direction)
Leeward side of mountain (downslope side, wind gets pushed up the windward side and drops down the Leeward side) Sometimes Rain shadows are on the Leeward side, as in less rain occurs here due to Adiabatic / Katabatic processes with the mountain.
Mountains have the ability to decrease the amounts of cyclonic rainfall.

Inversions:
    Commonly caused by radiation cooling from the surface at night.
    Wind sheer often exists at strong temperature inversions (a drastic change in ground speed can happen and your airplane will sink rapidly.)
Isothermal Layer:
    When the temperature does not change much with height, very stable air.

Rain comes in a number of types, know these:
    Convergent and cyclonic rainfall
        Caused by warm and cold fronts colliding.
        Warm fronts tend to have steady rain
        Cold fronts tend to have showery rain
    Orographic or release rainfall
        Air rises up a mountain, rains on the from side and on the aft side the air is dry so you have warm winds.
    Convectional rainfall
        Mainly in the summer, warm ground causes air to rise forming Cumulonimbus clouds. Daily ground heating in the summer encourages this cycle. Rain cools the air when it falls.

Surface heating is caused by
    Radiation - reflection of the earth's rays
    Conduction - warm air contacting cold air
    Advection - horizontal movement of air
    Convection - unequal surface heating

Lifting processes that can cause instability
    Convection - happens due to unequal surface heating
    Convergence - excess air rises as pressure systems meet
    Mechanical Turbulence - surface friction
    Orographic Lift - air moving up hills / mountains (anabatic)
    Frontal Lift - advancing air being pushed up by cold air on the bottom

Subsidence - is when air sinks resulting in compression and warming of air.  It also can result in the dissipation of clouds, typically on the leeward side of mountains.  It is a layer of warm air aloft caused by sinking or air that doesn't go all the way to the ground.