NIFE Weather 6-2-2 Mechanics Flashcards
2.185
Explain and identify gradient winds with respect to the isobars around pressure systems in the Northern Hemisphere.
Above 2000’ AGL
Shown via isobars - from high to lows
High pressure results from:
- descending air
- Creates horizontal diverging force (PGF)
- flows clockwise
Low pressure results from:
- Ascending air
- Creates horizontal converging force (PGF)
- counter-clockwise
2.186
Explain and identify the surface wind direction with respect to the gradient winds in a pressure system in the Northern Hemisphere
Pressure Gradient Force and Coriolis force balance to create flows.
- Parallel to isobars.
- Clockwise around Highs.
- Counterclockwise around Lows.
Gradient winds.
- Found above 2,000 feet AGL.
Surface winds (below 2,000 feet AGL).
- Friction reduces wind speed.
- Coriolis force shifts wind direction toward isobars.
- New balance of forces.
- Wind blows across the isobars (45º).
2.187
Describe the jet stream
-A narrow band of strong winds 50kts or more that meanders vertically and horizontally around the hemisphere in wave-like patterns.
- Ave height: 30000ft
- 1000 to 3000 miles length
- 100 to 400 miles width
- 3000 to 7000 feet in depth
- Average 100-150 knots
- Flows West to East
2.188
Describe sea breezes
- Onshore wind, blowing from the sea (cold air over water replaces warm air on land)
- Day time
2.189
Describe land breezes
-At night cooler on land air moves over water producing wind moving offshore.
2.190
Define the term front
-An area of discontinuity that forms between two contrasting air masses when they are adjacent to each other
OR
-a border, boundary, or line between air masses
2.191
Describe the discontinuities used to locate and classify fronts
Temperature
- Warm
- Cold
Dew Point
- Determines air mass boundary
- larger contrast produces more severe weather
Pressure
- Falls ahead and rises after front passes
Wind
- Usually shifts 90* clockwise after front passes
2.192
Describe the characteristics of cold fronts
- Leading edge of an advancing cold air mass.
- Colder (denser) air mass is overtaking and wedging underneath a relatively warmer (less dense) air mass.
- Unstable conditions
- Moves SE at 20 knots
- Wind switch from SW to from NW
- Recognize by long line of cumulus clouds
2.192
Describe warm front
- Boundary of the advancing warm air mass that is overtaking and replacing a colder air mass.
- Warmer (less dense) air rides up and over the cold air mass
- Stable Conditions
- Moves NE at 15 Knots
- Winds from SE shift to from SW
- Recognize by straisform cloud and steady precip
2.192
Describe stationary fronts
- Frontal border between the air masses shows little or no movement
- Neither air mass is replacing the other
- Shown by alternating cold warm front symbols and colors
- 180* wind shift
2.192
Describe occluded front
- Forms when a faster moving cold front overtakes a slower moving warm front
- Either cold or warm depending on which stays in contact with surface
- Winds shift 180*
- Most severe weather location 100NM South to 300 NM North of intersection
2.193
Describe the characteristics of a squall line
- A line of violent thunderstorms occurring in low pressure trough
- Indicated by a dashed double dotted purple line.
- Develop 50-300 miles ahead of a cold front and roughly parallel to it.
- Worst in late afternoon/evening
- 90 degree wind shift from SW to NW
2.194
Explain the relationship between flight conditions and atmospheric stability
FATVIPWC Chart
2.195
Describe the three characteristics of precipitation
- Showers: Sudden beginning and ending/ cumuliform clouds
- Continuous: Steady, intensity changes gradually/Stratiform Clouds
- Intermittent: Stops and restarts at least once during the hour/associated with either cloud
2.196
Describe the cloud types
- Low: Surface to 6500’ AGL
- Middle: 6500’ to 20000’ AGL (alto-)
- High: above 20000’ AGL (cirro-/cirrus-)
Cumuliform
- lumpy, billowy cloud showing a definite pattern
- Moist/Unstable air with showery precipitation (like Florida)
Stratiform:
- Uniform base, horizontal sheet like layer
- Moist/Stable air, constant precipitation (like Seattle)
Special:
- Extensive vertical limits
- nimbo/nimbus
2.199
Describe the four methods of lifting
- Convergence: Two air masses force the air up
- Orographic: Terrain lifts the wind (i.e. mountains, buildings)
- Frontal: Cold fronts push warm air up
- Thermal: Sun heats surface air causing it to rise
2.2
Describe stability with respect to lifted air
Stability is determined by the temp of the surrounding air. If air returns to normal after lifting action, it is stable. If it continues to rise, it is unstable.
- Stable: colder air settles when lifting action is removed
- Unstable: Warmer air continues to rise after lifting action is removed
- Neutral: Air of the same temperature remains at the point of where the lifting action was removed
