Weather

Question 1

State the general characteristics in regard to the flow of air around high and low pressure systems in the Northern Hemisphere.

Answer 1

Low Pressure — inward, upward, and counterclockwise


High Pressure — outward, downward, and clockwise


Question 2

What is a “trough”?

Answer 2

A trough (also called a trough line) is an elongated area of relatively low atmospheric pressure. At the surface when air converges into a low, it cannot go outward against the pressure gradient, nor can it go downward into the ground; it must go upward. Therefore, a low or trough is an area of rising air. Rising air is conducive to cloudiness and precipitation; hence the general association of low pressure and bad weather.


Question 3

What is a “ridge”?

Answer 3

A ridge (also called a ridge line) is an elongated area of relatively high atmospheric pressure. Air moving out of a high or ridge depletes the quantity of air; therefore, these are areas of descending air. Descending air favors dissipation of cloudiness; hence the association of high pressure and good weather.


Question 4

What are the standard temperature and pressure values for sea level?

Answer 4

15°C and 29.92” Hg

Question 5

What are “isobars”?

Answer 5

An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure.


Question 6

If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information will this provide?

Answer 6

The spacing of isobars on these charts defines how steep or shallow a pressure gradient is. When isobars are spaced very close together, a steep pressure gradient exists which indicates higher wind speeds. A shallow pressure gradient (isobars not close together) usually means wind speeds will be less.

Question 7

What causes the winds aloft to flow parallel to the isobars?

Answer 7

The Coriolis force.

Question 8

Why do surface winds generally flow across the isobars at an angle?

Answer 8

Surface friction.

Question 9

At what rate does atmospheric pressure decrease with an increase in altitude?

Answer 9

1” Hg per 1,000 feet

Question 10

What does “dew point” mean?

Answer 10

Dew point is the temperature to which a sample of air must be cooled to attain the state of saturation.

Question 11

When temperature and dew point are close together (within 5°), what type of weather is likely?

Answer 11

Visible moisture in the form of clouds, dew, or fog. Also, these are ideal conditions for carburetor icing.

Question 12

What factor primarily determines the type and vertical extent of clouds?

Answer 12

The stability of the atmosphere.

Question 13

How do you determine the stability of the atmosphere?

Answer 13

Unstable air is indicated when temperature decreases uniformly and rapidly as you climb (approaching 3°C per 1,000 feet). If temperature remains unchanged or decreases only slightly with altitude, the air tends to be stable. Instability is likely when air near the surface is warm and moist. Surface heating, cooling aloft, converging or upslope winds, or an invading mass of colder air may lead to instability and cumuliform clouds.

Question 14

List the effects of stable and unstable air on clouds, turbulence, precipitation and visibility.

Answer 14

Stable. Unstable
Clouds Stratiform Cumuliform
Turbulence Smooth Rough
Precipitation Steady Showery
Visibility Fair to Poor Good

Question 15

At what altitude above the surface would the pilot expect the bases of cumuliform clouds if the surface temperature is 82° and the dew point is 62°?

Answer 15

You can estimate the height of cumuliform cloud bases using surface temperature/dewpoint spread. Unsaturated air in a convective current cools at about 5.4°F (3.0°C) per 1,000 feet; dew point decreases at about 1°F (5/9°C). Thus, in a convective current, temperature and dew point converge at about 4.4°F (2.5°C) per 1,000 feet. You can get a quick estimate of a convective cloud base in thousands of feet by rounding the values and dividing into the spread. When using Fahrenheit, divide by 4 and multiply by 1,000. This method of estimating is reliable only with instability, clouds and during the warmer part of the day.


82 – 62 = 20

20 ÷ 4 = 5

5 x 1,000 = 5,000 feet AGL


Question 16

During your preflight planning, what type of meteorological information should you be aware of with respect to icing?

Answer 16

a. Location of fronts — A front’s location, type, speed, and direction of movement.

b. 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.

c. Freezing level(s) — Important when determining how to avoid icing and how to exit icing conditions if accidentally encountered.

d. Air temperature and pressure — Icing tends to be found in low-pressure areas and at temperatures at or around freezing.

Question 17

What is the definition of the term freezing level and how can you determine where that level is?

Answer 17

The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0°C. It is possible to have multiple freezing layers when a temperature inversion occurs above the defined freezing level. A pilot can use current icing products (CIP) and forecast icing products (FIP), as well as the freezing level graphics chart to determine the approximate freezing level. Other potential sources of icing information are: area forecasts, PIREPs, AIRMETs, SIGMETs, surface analysis charts, low-level significant weather charts, and winds and temperatures aloft (for air temperature at altitude).

Question 18

What conditions are necessary for structural icing to occur?

Answer 18

Visible moisture and below freezing temperatures at the point moisture strikes the aircraft.

Question 19

Name the main types of icing an aircraft may encounter in-flight.

Answer 19

Structural, induction system, and instrument icing.

Question 20

Name the three types of structural icing that may occur in flight.

Answer 20

Clear ice — forms after initial impact when the remaining liquid portion of the drop flows out over the aircraft 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 remaining after initial impact freezes rapidly before the drop has time to spread out over aircraft 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.


Question 21

What action is recommended if you inadvertently encounter icing conditions?

Answer 21

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.

Question 22

Is frost considered to be hazardous to flight? Why?

Answer 22

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. Even a small amount of frost on airfoils may prevent an aircraft from becoming airborne at normal takeoff speed. It is also possible that, once airborne, an aircraft could have insufficient margin of airspeed above stall so that moderate gusts or turning flight could produce incipient or complete stalling.

Question 23

What factors must be present for a thunderstorm to form?

Answer 23

Sufficient water vapor
An unstable lapse rate
*An initial upward boost (lifting) to start the storm process in motion

Question 24

What are the three stages of a thunderstorm?

Answer 24

Cumulus stage — Updrafts cause raindrops to increase in size.

Mature stage — Rain at earth’s surface; it falls through or immediately beside the updrafts; lightning; perhaps roll clouds.

Dissipating stage — Downdrafts and rain begin to dissipate.

Question 25

What is a “temperature inversion”?

Answer 25

An inversion is an increase in temperature with height — a reversal of the normal decrease with height. An inversion aloft permits warm rain to fall through cold air below. Temperature in the cold air can be critical to icing. A ground-based inversion favors poor visibility by trapping fog, smoke, and other restrictions into low levels of the atmosphere. The air is stable, with little or no turbulence.

Question 26

Basic ways fog may form

Answer 26

1) Cooling air to the dew point.

2) Adding moisture to the air near the ground.

Question 27

Types of Fog

Answer 27

• Radiation fog
*Advection fog

* Upslope fog
Precipitation-induced fog
Ice fog

Question 28

What causes radiation fog to form?

Answer 28

The ground cools the adjacent air to the dew point on calm, clear nights.

Question 29

What is advection fog, and where is it most likely to form?

Answer 29

Advection fog results from the transport of warm humid air over a cold surface. A pilot can expect advection fog to form primarily along coastal areas during the winter. Unlike radiation fog, it may occur with winds, cloudy skies, over a wide geographic area, and at any time of the day or night.

Question 30

What is upslope fog?

Answer 30

Upslope fog forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. Once the upslope wind ceases, the fog dissipates. Upslope fog is often quite dense and extends to high altitudes.

Question 31

Define the term “wind shear,” and state the areas in which it is likely to occur.

Answer 31

The rate of change of wind velocity (direction and/or speed) per unit distance; conventionally expressed as vertical or horizontal wind shear. It may occur at any level in the atmosphere but three areas are of special concern:


a) Wind shear with a low-level temperature inversion.
b) Wind shear in a frontal zone or thunderstorm.
c) Clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.

Question 32

Why is wind shear an operational concern to pilots?

Answer 32

Wind shear is an operational concern because unexpected changes in wind speed and direction can be potentially very hazardous to aircraft operations at low altitudes on approach to and departing from airports.

Question 33

What types of weather information will you examine to determine if wind shear conditions might affect your flight?

Answer 33

a) Terminal forecasts — any mention of low level wind shear (LLWS) or the possibility of severe thunderstorms, heavy rain showers, hail, and wind gusts suggest the potential for LLWS and microbursts.

b) METARs — inspect for any indication of thunderstorms, rain showers, or blowing dust. Additional signs such as warming trends, gusty winds, cumulonimbus clouds, etc., should be noted.

c) Severe weather watch reports, SIGMETS, and convective SIGMETS — severe convective weather is a prime source for wind shear and microbursts.

d) LLWAS (low level windshear alert system) reports — installed at 110 airports in the U.S.; designed to detect wind shifts between outlying stations and a reference centerfield station. 

e) PIREPs — reports of sudden airspeed changes on departure or approach and landing corridors provide a real-time indication of the presence of wind shear.

Question 34

What is the primary means of obtaining a weather briefing?

Answer 34

The primary source is an individual briefing obtained from a briefer at the AFSS/FSS. These briefings, which are tailored to your specific flight, are available 24 hours a day through the use of the toll-free number (1-800-WX BRIEF).

Question 35

What are some examples of other sources of weather information?

Answer 35

a) Telephone Information Briefing Service (TIBS) (AFSS).

b) Weather and aeronautical information available from numerous private industry sources. 

c) Direct User Access Terminal System (DUATS) can be accessed by pilots with a current medical certificate toll-free in the 48 contiguous states via personal computer. 

d) In Alaska, Transcribed Weather Broadcast (TWEB) and telephone access to the TWEB (TEL-TWEB).

Question 36

Where can you find a listing of AFSS/FSS and weather information numbers?

Answer 36

Numbers for these services can be found in the Airport/Facility Directory under the “FAA and NWS Telephone Numbers” section. They are also listed in the U.S. Government section of the local telephone directory.

Question 37

What types of weather briefings are available from an AFSS/FSS briefer?

Answer 37

Standard Briefing — Request when you are planning a flight and you have not received a previous briefing or have not received preliminary information through mass dissemination media (TIBS, TWEB in Alaska only, etc.).

Abbreviated Briefing — Request when you need information to supplement mass disseminated data, update a previous briefing, or when you need only one or two items.

Outlook Briefing — Request whenever your proposed time of departure is six or more hours from the time of the briefing; for planning purposes only.

Inflight Briefing — Request when needed to update a preflight briefing.

Question 38

What pertinent information should a weather briefing include?

Answer 38

• Adverse Conditions

• VFR Flight Not Recommended

• Synopsis

• Current Conditions

• Enroute Forecast

• Destination Forecast

• Winds Aloft

• Notices to Airmen (NOTAMs)

• ATC Delay

• Pilots may obtain the following from FSS briefers upon request: information on special use airspace (SUA) and SUA-related airspace, including alert areas, MOAs, MTRs (IFR, VFR, VR, and SR training routes), warning areas, and ATC assigned airspace (ATCAA); a review of the printed NOTAM publication; approximate density altitude data; information on air traffic services and rules; customs/immigration procedures; ADIZ rules; search and rescue; LORAN-C and military NOTAMs; runway friction measurement value NOTAMs; GPS RAIM availability; and other assistance as required.

Question 39

What is EFAS?

Answer 39

En route Flight Advisory Service (EFAS) is a service specifically designed to provide enroute aircraft with timely and meaningful weather advisories pertinent to the type of flight intended, route of flight, and altitude. In conjunction with this service, EFAS is also a central collection and distribution point for pilot reported weather information (PIREPs). EFAS provides communications capabilities for aircraft flying at 5,000 feet above ground level to 17,500 feet MSL on a common frequency of 122.0 MHz. It is also known as “Flight Watch.”

Question 40

What is HIWAS?

Answer 40

Hazardous In-flight Weather Advisory Service (HIWAS) is a continuous broadcast of in-flight weather advisories including summarized Aviation Weather Warnings, SIGMETs, Convective SIGMETs, Center Weather Advisories, AIRMETs, and urgent PIREPs. HIWAS is an additional source of hazardous weather information which makes this data available on a continuous basis. Navaids with HIWAS capability are depicted on sectional carts with an “H” in the upper right corner of the identification box. Where implemented, HIWAS alerts are broadcast on all except emergency frequencies once upon receipt by ARTCC, terminal facilities, and AFSS/FSSs.

Question 41

What is a “flight information service” (FIS)?

Answer 41

FIS is a method of receiving aviation weather and other operational data in the cockpit that augments traditional pilot voice communication with FSS or ATC facilities. It is not intended to replace traditional pilot and controller/FSS preflight briefings or inflight voice communications.

Question 42

What is a METAR and what are the two types?

Answer 42

A METAR is an hourly surface observation of conditions observed at an airport. There are two types of METAR reports — a routine METAR report that is transmitted every hour and an aviation selected special weather report (SPECI). This is a special report that can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information.

Question 43

Describe the basic elements of a METAR.

Answer 43

• Type of reports (METAR or SPECI)
• ICAO station identifier
• Date and time of report
• Wind
• Visibility
Runway visual range (RVR), as required.
Weather phenomena
Sky condition
Temperature/dew point group
Altimeter
Remarks (RMK), as required

Question 44

Describe several types of weather observing programs available.

Answer 44

• Manual Observations
• AWOS
• ASOS/AWSS

Question 45

What is AWOS?

Answer 45

Automated Weather Observing System

Consists of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast local, minute-by-minute weather data directly to the pilot. Observations will include the prefix AUTO in data.


Question 46

What is ASOS/AWSS?

Answer 46

Automated Surface Observing System/Automated Weather Sensor System

The primary U.S. surface weather observing systems. AWSS is a follow-on program that provides the identical data as ASOS. Both systems provide continuous minute-by-minute observations that generate METARs and other aviation weather information. Transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID, and are receivable to a maximum of 25 NM from the station and a maximum altitude of 10,000 feet AGL. Observations made without human intervention will include the modifier “AUTO” in the report data.


Question 47

What are PIREPs (UA), and where are they usually found?

Answer 47

The two types of PIREPs (routine, or “UA,” and urgent, or “UUA”) contain information concerning weather as observed by pilots en route. Required elements for all PIREPs are message type, location, time (in UTC), flight level (altitudes are MSL), type of aircraft, and at least one weather element encountered (visibility in SM, distances in NM). A PIREP (abbreviation for “pilot reports”) is usually transmitted as an individual report but can be appended to a surface aviation weather report or placed into collectives.

Question 48

What are Radar Weather Reports (SD)?

Answer 48

A radar weather report (SD/ROB) contains information about precipitation observed by weather radar. It is a textual product derived from the WSR-88D NEXRAD radar without human intervention. Reports are transmitted hourly and contain the following: location ID, time, configuration (CELL, LN, and AREA), coverage, precipitation type and intensity, location, maximum tops, cell movement, and remarks. The resolution of an SD/ROB is very coarse, up to 80 minutes old, and should only be used if no other radar information is available.

Question 49

What are Terminal Aerodrome Forecasts (TAFs)?

Answer 49

A terminal aerodrome forecast (TAF) is a concise statement of the expected meteorological conditions significant to aviation for a specified time period within five statute miles (SM) of the center of the airport’s runway complex (terminal).

Question 50

Define “aviation area forecast.”

Answer 50

Abbreviated as “FA,” this is a forecast of specified weather phenomena covering a flight information region or other area designated by the meteorological authority. Pilots should use the area forecast (in conjunction with AIRMETs, SIGMETs, convective SIGMETs, CWAs, etc.), to determine forecast en route weather and to interpolate conditions at airports that do not have a terminal aerodrome forecast (TAF). FAs are issued 3 times daily for each of the 6 areas in the contiguous 48 states. FAs are also issued for the Gulf of Mexico, the Caribbean, Hawaii, and Alaska.

Question 51

What information is provided by an FA?

Answer 51

Area forecasts are issued for the conterminous U.S. and cover the airspace between the surface and 45,000 feet AMSL. They include:


a. Synopsis — brief discussion of the synoptic weather affecting the FA area during the 18-hour valid period.

b. Clouds and weather — description of the clouds and weather for the first 12-hour period for each state or group of states, including:


• Cloud amount (SCT, BKN or OVC) for clouds with bases higher than or equal to 1,000 feet AGL and below FL180,

• Cloud bases and tops (AMSL) associated with the above,

• Precipitation,

• Visibilities between 3 and 6 SM and obstruction(s) to visibility,

• Sustained surface winds 20 knots or greater.


c. 12 to 18-hour categorical outlook — IFR, marginal VFR (MVFR), or VFR, including expected precipitation and/or obstruction(s) to visibility.


Question 52

What are Inflight Aviation Weather Advisories (WST, WS, WA)?

Answer 52

Inflight aviation weather advisories are forecasts to advise en route aircraft of development of potentially hazardous weather in 3 types: the SIGMET, the convective SIGMET, and the AIRMET (text or graphical product). All heights are referenced MSL, except in the case of ceilings (CIG), which indicate AGL.

Question 53

What is a Convective SIGMET?

Answer 53

Convective SIGMETs (WST) implies severe or greater turbulence, severe icing and low-level wind shear. They may be issued for any convective situation which the forecaster feels is hazardous to all categories of aircraft. Convective SIGMET bulletins are issued for the Eastern (E), Central (C) and Western (W) United States (Convective SIGMETs are not issued for Alaska or Hawaii). Bulletins are issued hourly at H+55. Special bulletins are issued at any time as required and updated at H+55. The text of the bulletin consists of either an observation and a forecast, or just a forecast. The forecast is valid for up to 2 hours.


a. Severe thunderstorm due to:


• Surface winds greater than or equal to 50 knots.

• Hail at the surface greater than or equal to 3⁄4 inches in diameter.

• Tornadoes


b. Embedded thunderstorms

c. A line of thunderstorms

d. Thunderstorms producing greater than or equal to heavy precipitation that affects 40% or more of an area at least 3,000 square miles.


Question 54

What is a SIGMET (WS)?

Answer 54

A SIGMET (WS) advises of non-convective weather that is potentially hazardous to all aircraft. SIGMETs are issued for the six areas corresponding to the FA areas. The maximum forecast period is four hours. In the conterminous U.S., SIGMETs are issued when the following phenomena occur or are expected to occur:


a. Severe icing not associated with a thunderstorm;

b. Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms;

c. Duststorms or sandstorms lowering surface or inflight visibilities to below 3 miles;

d. Volcanic ash.

Question 55

What is an AIRMET (WA)?

Answer 55

Advisories of significant weather phenomena that describe conditions at intensities lower than those which require the issuance of SIGMETs, intended for use by all pilots in the preflight and enroute phase of flight to enhance safety. AIRMET information is available in two formats: text bulletins (WA) and graphics (G-AIRMET). They are issued on a scheduled basis every 6 hours beginning at 0245 UTC. Unscheduled updates and corrections are issued as necessary.


Each AIRMET Bulletin includes an outlook for conditions expected after the AIRMET valid period. AIRMETs contain details about IFR, extensive mountain obscuration, turbulence, strong surface winds, icing, and freezing levels.

Question 56

What are the different types of AIRMETs?

Answer 56

AIRMET Sierra: describes IFR conditions and/or extensive mountain obscurations.

AIRMET Tango: describes moderate turbulence, sustained surface winds of 30 knots or greater, and/or nonconvective low-level wind shear.

AIRMET Zulu: describes moderate icing and provides freezing level heights.

Question 57

Describe the winds and temperature aloft forecasts (FB).

Answer 57

Winds and temperature aloft forecasts are computer prepared forecasts of wind direction, wind speed, and temperature at specified times, altitudes, and locations. They are produced 4 times daily for specified locations in the continental United States, Hawaii, Alaska and coastal waters, and the western Pacific Ocean. Amendments are not issued to the forecasts. Wind forecasts are not issued for altitudes within 1,500 feet of a location’s elevation.

Question 58

What valuable information can be determined from Winds and Temperatures Aloft Forecasts (FB)?

Answer 58

Most favorable altitude — based on winds and direction of flight.

Areas of possible icing — by noting air temperatures of +2°C to -20°C. 

Temperature inversions.

Turbulence — by observing abrupt changes in wind direction and speed at different altitudes.

Question 59

What are Center Weather Advisories (CWA)?

Answer 59

A Center Weather Advisory (CWA) is an aviation warning for use by aircrews to anticipate and avoid adverse weather conditions in the en route and terminal environments. The CWA is not a flight planning product; instead it reflects current conditions expected at the time of issuance and/or is a short-range forecast for conditions expected to begin within 2 hours of issuance. CWAs are valid for a maximum of 2 hours. If conditions are expected to continue beyond the 2-hour valid period, a statement will be included in the CWA.

Question 60

Give some examples of current weather charts available at the FSS or NWSO used in flight planning.

Answer 60

Surface analysis chart
Weather depiction chart
Radar summary chart
Short-range surface prognostic chart
Significant weather prognostic chart
Convective outlook chart
*Constant pressure analysis chart

Question 61

What is a surface analysis chart?

Answer 61

This is a computer-prepared chart that covers the contiguous 48 states and adjacent areas. The chart is transmitted every three hours. The surface analysis chart provides a ready means of locating pressure systems and fronts. It also gives an overview of winds, temperatures and dew point temperatures at chart time. When using the chart, keep in mind that weather moves and conditions change. Using the surface analysis chart in conjunction with other information gives a more complete weather picture.

Question 62

What information does a weather depiction chart provide?

Answer 62

The weather depiction chart is computer-generated (with a weather observer’s analysis of fronts) from METAR reports. This chart gives a broad overview of the observed flying category conditions at the valid time of the chart. The chart begins at 01Z each day, is transmitted at three-hour intervals, and is valid at the time of the plotted data. The plotted data for each station area are: total sky cover, cloud height or ceiling, weather and obstructions to vision and visibilities. The weather depiction chart is an ideal place to begin in preparing for a weather briefing and flight planning. From this chart one can get a “bird’s-eye” view of areas of favorable and adverse weather conditions at chart time.

Question 63

Define the terms: LIFR, IFR, MVFR and VFR.

Answer 63

LIFR Low IFR — ceiling less than 500 feet and/or visibility less than 1 mile.

IFR Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.

MVFR Marginal VFR — ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive.

VFR Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.


Question 64

What are radar summary charts?

Answer 64

Computer-generated graphical display of a collection of automated radar weather reports (SDs). The chart displays areas of precipitation as well as information about type, intensity, configuration, coverage, echo top, and cell movement of precipitation. Severe weather watches are plotted if they are in effect when the chart is valid. The chart is available hourly with a valid time of 35 minutes past each hour.


This chart aids in preflight planning by identifying general areas and movement of precipitation and/or thunderstorms. Displays drops or ice particles of precipitation size only; it does not display clouds and fog. Therefore, since the absence of echoes does not guarantee clear weather, and cloud tops will most likely be higher than the tops of the precipitation echoes detected by radar, the radar summary chart must be used along with other charts, reports, and forecasts for best effectiveness.

Question 65

What are short-range surface prognostic charts?

Answer 65

Called “progs,” these charts portray forecasts of selected weather conditions at specified valid times (12, 24, 36, and 48 hour progs). Each valid time is the time at which the forecast conditions are expected to occur, made from a comprehensive set of observed weather conditions. The observed conditions are extended forward in time and become forecasts by considering atmospheric and environmental processes. Forecast information for the surface to 24,000 feet is provided by the low-level significant weather prog chart. Forecast information from above 24,000 to 60,000 feet is provided by the high-level significant weather prog chart.

Question 66

Describe a U.S. low-level significant weather prog chart.

Answer 66

It is a “Day One” forecast of significant weather for the conterminous U.S., pertaining to the layer from surface to FL240 (400 mb). With two forecast periods, 12 hours and 24 hours, the chart is composed of four panels. The two lower panels depict the 12- and 24‑hour surface progs, and the two upper panels depict the 12- and 24-hour significant weather progs. Issued four times a day at 00Z, 06Z, 12Z, and 18Z. Covered are forecast positions and characteristics of pressure systems, fronts, and precipitation. Much insight can be gained by evaluating the individual fields of pressure patterns, fronts, precipitation, weather flying categories, freezing levels, and turbulence displayed on the chart.

Question 67

Describe a mid-level significant weather (SIGWX) chart.

Answer 67

The mid-level significant weather chart provides a forecast and an overview of significant en route weather phenomena over a range of flight levels from 10,000 feet MSL to FL450, and associated surface weather features. The chart is a “snapshot” of weather expected at the specified valid time and depicts numerous weather elements that can be hazardous to aviation. The AWC issues the 24-hour mid-level significant weather chart four times daily.

Question 68

What is a convective outlook chart?

Answer 68

The convective outlook chart depicts areas forecast to have the potential for severe (tornado, wind gusts 50 knots or greater, or hail 3⁄4 inch diameter size or greater) and non-severe (general) convection and specific severe weather threats during the following three days. The chart defines areas of slight risk (SLGT), moderate risk (MDT) or high risk (HIGH) of severe thunderstorms for a 24-hour period beginning at 1200 UTC. The Day 1 and Day 2 Convective Outlooks also depict areas of general thunderstorms (GEN TSTMS), while the Day 1, Day 2, and Day 3 Convective Outlooks may use SEE TEXT for areas where convection may approach or slightly exceed severe criteria.

Question 69

What are constant pressure analysis charts?

Answer 69

Any surface of equal pressure in the atmosphere is a constant pressure surface. A constant pressure analysis chart is an upper air weather map where all information depicted is at the specified pressure of the chart. From these charts, a pilot can approximate the observed air temperature, wind, and temperature-dewpoint spread along a proposed route. They also depict highs, lows, troughs, and ridges aloft by the height contour patterns resembling isobars on a surface map. Twice daily, five constant pressure charts are issued from observed data obtained at 00Z and 12Z:


850 mb5,000 ft
700 mb10,000 ft
500 mb18,000 ft
300 mb30,000 ft
200 mb39,000 ft