u13 Flashcards
what is an airmass
characteristics
where is the best source region
airmass = body of air with same temperature and moisture in the horizontal
uniform temp/pressure = low wind variation
high P, large, flat area
t/f: since an airmass has uniform temperature and moisture, it doesn’t experience any weather phenomena
false it still has weather
weather in an airmass is determined by what 3 things
moisture
stability
cooling or heating processes present
which air masses are most common in canada (from north to south) and when do they form:
cA = winter
mA = summer and winter
mP = summer and winter
mT = summer
which air masses are uncommon to see in canada and why
cP: forms in southern canada and moves downwards to USA
cT: only few locations it can form in (arizona) and even if it tries to move upwards to canada it’s blocked by the rocky mountains
continental arctic airmass (cA)
- characteristics
- from where
- season it appears in canada and why doesn’t it show up year round
cold and dry
arctic circle
moves downwards to canada in winter
not summer because 24h daylight warms the arctic
maritime arctic airmass (mA)
- characteristics
- where does it appear in winter
- where does it appear in the summer
- what type of weather does it bring to the prairies
cold and moist
winter = along coast
summer = through middle of canada (from cA passing over numerous lakes in northern canada it becomes mA)
moist air from pactific passes over rockies (looses moisture) = brings dry air into prairies = clear and nice weather
maritime polar airmass (mP)
- characteristics
- from where
- what season
- type of weather it brings
cool and moist
along coast summer
summer and winter
cloudy and damp weather
maritime tropical airmass (mT)
- characteristics
- from where
- what season
- type of weather it brings
hot and moist
gulf of mexico
mostly summer but sometimes winter
hot humid days
when an airmass moves, it takes on the characteristics of the surface they pass over. that airmass gets modified from _________
below
what happens when cA airmass moves over a warm ocean?
cA gets heated from below + moisture added to it = lower levels of airmass warm and rise -> clouds = unstable
what happens when an mT airmass moves over nunavut?
warm, moist airmass moves over a cold surface = inversion = lower levels cool and form fog/stratus clouds = stable
at the tropopause, the temperature of the WARM airmass is ________ than a COLD airmass. why?
COLDER
warm airmass reaches higher troposphere heights = more adiabatic cooling
cold air masses move ______ than warm airmass
faster
weather at a front is determined by:
_______ of the warm airmass
_______ of the cold airmass
______ of the front
stability and moisture
speed
slope
name of a front is determined by the motion of _____ air
cold
at the front is a ______ pressure zone
low
cold front:
- slope
- speed
- depth
- order of clouds you see as a cold front passes over your town
- how long does it last
- cold front causes the wind to ______
steep (1.5%)
fast
50NM
CB, NS, AS, CI
fast front = short time for bad weather
wind Veers
warm front:
- slope
- speed
- order of clouds you see as a warm front passes over your town
- how long does it last
shallow (0.5%)
slow
CI, CS, AS, NS
slow moving front = weather lasts a long time
as the cold front passes over your town, what happens to the dew point and why
dew point DECREASES (the temp would have to fall lower in order to be saturated)
because as the cold front passes, CB created and lots of rain falls. so the air is getting drier = decrease dew point
as the warm front passes over your town, what happens to the dew point and why
dew point INCREASES (the air will be saturated at higher temperature)
because as the warm/moist front passes, water vapour is added to your air so the air will be saturated at higher temperature = increase dew point
ice pellets and freezing rain occur ________ of a winter warm front
right ahead
what is an occluded front (aka trowal)
explain the weather at a trowal (ahead and behind the trowal)
when a cold front catches up to a warm front and overtaking it and pushing it upwards (trough of warm air aloft)
ahead of the trowal = warm front weather
behind the trowal = cold front weather
what is a stationary front and what’s the weather like there
which direction does wind flow in relation to the front
unmoving front = prolonged clouds and precipitation
wind flows parallel to front
when flying through a stationary front directly perpendicular to it, how do i adjust my heading to account for wind
wind VEERS in a front (now coming from my right) so adjust heading right
frontogenesis vs frontolysis.
explain how the temperature gradient is affected during these processes, and what does that mean
frontogenesis = front being formed
- there’s a drastic temperature difference between the two air masses and a front is about to form
frontolysis = front dissipating
- temperature difference between the air masses is decreasing (one of the airmasses is being modified)
t/f. an upper front is an occlusion
false
an upper front is when frontal weather gets pushed aloft but it’s caused by terrain (warm front forced upwards by a mountain but cold air stays on surface)
when an upper warm front passes over a town, what changes would an observer on the ground feel?
wind
temperature
precipitation
surface wind = no change
surface temperature = no change
precipitation = will see
when an upper warm front passes over a town, what changes would a plane in the sky feel?
wind
temperature
precipitation
winds = veer
temperature = gets warmer
precipitation = will see
explain frontal fog/precipitation fog
a warm front makes rain = rain falls into cold air below = cold air gets saturated = fog forms
a fast moving cold front
- occurs when
- weather it causes
- what creates a protruding nose of cold air
summer
intense thunderstorms
surface friction creates protruding nose of cold air
explain how an upper cold front would form
- mA air forced over a mountain
- cA is on the other side of the mountain
- cA is colder/denser than mA, so the mA sits on top = upper cold front
explain how an upper warm front can form due to daytime heating
there’s a warm front on the surface
daytime heating -> the temperature difference between the warm and cold airmass doesn’t exist anymore at the surface
but there’s still a temp difference between the airmasses aloft, so aloft, the warm front still exists = “upper warm front”
what is the weather like at an occluded front in winter
in winter, freezing rain and severe icing because rain aloft of the occluded warm air falls through freezing temperatures near the cold surface
what are frontal waves and how are they formed
what are stable vs unstable frontal waves
frontal wave = wave like disturbances on stationary fronts. normally wind flows parallel to stationary front, but if upper winds shift or front starts to move then a wave will form
stable frontal waves don’t get worse
unstable frontal waves get so big that the cold front can catch up to the warm front and form a trowal
