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
