C. Weather Info Flashcards
What is atmospheric stability?
Is the property of ambient air that either enhances or suppresses vertical motion of air parcels and determines which type of clouds and precipitation a pilot will encounter.
What is a surface analysis chart?
Surface analysis charts are analyzed charts of surface weather observations. The chart depicts the distribution of several items including sea level pressure, the position of highs and lows, ridges, troughs, the location and character of fronts, and the various boundaries such as dry lines, outflow boundaries, sea-breeze fronts, and convergence lines.
The chart is produced eight times daily.
How does the air flow around high and low pressure systems in the N. hemisphere?
Low Pressure - inward, upward, and counterclockwise
High Pressure - outward, downward, and clockwise
What kind of weather can you expect in a low-pressure system? In a high-pressure system?
A low-pressure system is characterized by rising air, which is conductive to cloudiness, precipitation, and bad weather.
A high-pressure system is an area of descending air which tends to favor dissipation of cloudiness and good weather
What are the type of fronts?
Cold front - cold air replaces warm air.
Speed - 20-35 mph… steeper frontal slope… cold fronts typically have violent wx.
Warm front - warm air replaces cold air.
10-25 mph… low ceilings, poor visibility, and rain.
Stationary front - when cold and warm pushes against each other.
Occluded front - cold front catches warm front and are moving in same direction.
What are the general weather characteristics near a cold front and a warm front?
Cold Front - towering cumulus or cumulonimbus, heavy rain accompanied by lightning, thunder and/or hail; tornadoes possible; during passage, poor visibility, winds variable and gusting; temp/dew point and pressure drop rapidly.
Warm Front - stratiform clouds, drizzle, low ceilings, and poor visibility; variable winds; rise in temp.
What is a trough?
A trough, called a trough line, is an elongated area of relatively low atmospheric pressure.
What is a ridge?
A ridge, also called a ridge line, is an elongated area of relatively high atmospheric pressure.
What is the standard temp. and pressure?
15 C (59 F) 29.92 Hg
What are short-range surface prognostic charts?
Short-range prog charts provide a forecast of surface pressure systems, fronts and precipitation for a 2.5 day period. Conditions are divided into 5 forecast periods: 12, 18, 24, 48, and 60h.
Issued 4 times daily and can be used to obtain the progression of surface weather during the included periods
What are isobars?
An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure.
What is indicated by isobars being close together?
When isobars are spaced very close together, a steep pressure gradient exists which indicating higher wind speeds. A shallow pressure gradient usually means winds will be calmer.
What causes the winds aloft to flow parallel to the isobars?
The Coriolis force.
Why do surface winds generally flow across the isobars at an angle?
Surface friction
What is a METAR and what are the two types?
A METAR is an hourly surface observation of conditions observed at an airport.
There are two types of METAR reports.
METAR report every hour.
SPECI is an amended observation for weather.
What are TAFs?
A terminal aerodrome forecast is a weather forecast.
TAFs are issued at least four times a day, every six hours usually covering 24-30 hours.
What is AIRMET? (STZ)
PHAK 13
Airmens Meteorological Information
Issued every 6 hours
Potentially hazardous to light aircraft
Sierra: IFR, extensive mountain obscuration
Tango: turbulence, strong surface winds > 30 knots, non-convective low-level wind shear
Zulu: icing, and freezing levels
What is a SIGMET? (SSSDV)
PHAK 13-12/AIM 7-1-6
Significant Meteorological
Non convective weather potentially hazardous to all aircraft
Not associated with thunderstorms
Valid for 4 hours or 6 hours for hurricanes
Severe icing not associated with thunderstorms
Severe or extreme turbulence or CAT not associated with a t-storm
Sandstorms lowering surface visibilities to below 3 miles
Duststorms lowering surface visibilities to below 3 miles
Volcanic ash
Convective SIGMET?
6 thunderstorm reasons (SHLEPT)
AIM 7-1-6
Hazardous to all aircraft.
2 hours
Severe thunderstorms due to:
1. Surface winds greater than or equal to 50 knots
2. Hail at surface greater than or equal to 3/4 in. in diameter
3. Tornadoes
4. Embedded thunderstorms
5. Line of thunderstorms
6. precipitation affecting 40% or more of 3,000 sq.mi.
What factors must be present for a thunderstorm to form?
Water vapor
Unstable atmosphere
Upward drafts
What does dew point mean?
Dew point is the temperature to which a sample of air must be cooled to attain the state of saturation.
When temperature and dew point are close together, within 5 degrees, what can you expect?
Visible moisture in the form of clouds or fog.
Define LIFR, IFR, MVFR, VFR:
LIFR - Low IFR ceiling less than 500’ and/or visibility less than 1 miles
IFR - Ceiling 500’ to less than 1,000’ and visibility 1 to less than 3 miles
MVFR - ceiling 1,000-3,000’ and/or visibility 3-5 miles inclusive
VFR - ceiling greater than 3,000’ and visibility greater than 5miles including clear sky
At what rate does atmospheric pressure decrease with an increase in altitude?
1” Hq per 1,000 Feet
What factor primarily determines the type and vertical extent of clouds?
The stability of the atmosphere.
What is atmospheric stability?
The stability of the atmosphere depends on its ability to resist vertical motion.
List the effects of stable and unstable air on clouds, turbulence, precipitation and visibility:
Stable: Clouds: Stratiform Turbulence: Smooth Precipitation: Steady Visibility: Fair to Poor
Unstable Clouds: Cumuliform Turbulence: Rough Precipitation: Showery Visibility: Good
When significant precipitation is occurring at the surface, how thick can you expect the clouds to be?
Significant precipitation usually requires clouds to be at least 4,000 feet thick. The heavier the precipitation, the thicker the clouds are likely to be.
During your preflight planning, what type of meteorological information should you be aware of with respect to icing?
Location of fronts - A front’s location, type, speed, and direction of movement.
Cloud layers - The location of cloud bases and tops, which is valuable when determining if you will be able to climb above icing layers or descend beneath those layers into warmer air; reference PIREPs and area forecasts.
Freezing levels - Important when determining how to avoid icing and how to exit icing conditions if accidentally encountered.
Air temperature and pressure - Icing tends to be found in low-pressure areas and at temperatures at or around freezing.
What is the definition of the term freezing level and how can you determine where that level is?
The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0 degrees C.
What conditions are necessary for structural icing to occur?
Visible moisture and below freezing temp at the point moisture strikes the aircraft.
What are the main types of icing an aircraft may encounter in-flight?
Structural, induction, and instrument icing.
What types of structural icing may occur in flight?
Clear ice - forms after initial impact when the remaining liquid portion of the drop flow out over the A/C surface, gradually freezing as a smooth sheet of solid ice
Rime ice - forms when drops are small, such as those in stratified clouds or light drizzle. The liquid portion remains after initial impact freezes rapidly before the drop has time to spread out over the A/C surface
Mixed ice - forms when drops vary in size or when liquid drops are intermingled with snow or ice particles. The ice particles become imbedded in clear ice, building a very rough accumulation
What action is recommended if you inadvertently encounter icing conditions?
The first course of action should be to leave the area of visible moisture. This might mean descending to an altitude below the cloud bases, climbing to an altitude above the cloud tops, or turning to a different course. Turn on pitot heat.
Is frost considered to be hazardous to flight? Why?
Yes, because while frost does not change the basic aerodynamic shape of the wing, the roughness of its surface spoils the smooth flow of air, thus causing a slowing of airflow. This slowing of the air causes early airflow separation, resulting in a loss of lift.
What is a Graphical Forecast for Aviation (GFA)?
The GFA is intended to provide the necessary aviation weather information as a complete picture of the weather that may impact flight in the US. The webpage includes observational data, forecasts, and warnings that can be viewed from 14h in the past to 15h in the future, including thunderstorms, clouds, flight category, precipitation, icing, turbulence and wind.
What is a convective outlook chart?
The convective outlook chart depicts ares of forecast to have the potential for sever tornado, wind gust 50 kt or more, or hail 3/4” or greater and non-sever general convection and specific sever weather threats during the following 3 days. The chart defines areas of slight risk SLGT, moderate risk MDT, or high risk HIGHT of severe thunderstorms for a 24-h period beginning at 1200 UTC.
How do you read wind charts?
By the barbs, small bard indicates 5, big barb 10, triangle 50.
