Reference: PHAK Chapter 12 and 13, AC 00-45H Weather Services, AC 91-92

Learning Objective (Index)

• Learning Objective (Index)
• Homework
• Intro
• What Creates The Weather?
• Importance of the Weather in Aviation
• WEATHER SERVICES
• Flight Service Station (FSS)
• Weather Briefings 1-800-WX-BRIEF
• Standard Briefing
• Abbreviated Briefing
• Outlook Briefing
• Weather Briefing Format
• 1800WXBRIEF.COM
• Web Page for Weather Information
• Types Of Aviation Weather Products
• Observations
• Aviation Routine Weather Report (METAR)
• METAR Brakedown
• Reportable Contractions for Sky Conditions
• METAR Notation for Reporting Present Weather
• Special Weather Report (SPECI)
• Pilot Weather Report (PIREPs)
• Forecasts
• Terminal Aerodrome Forecast (TAF)
• Graphical Forecast of Aviation Overview (GFA)
• Coverage Area
• GFA Tutorial Video
• Airmen’s Meteorological Information (AIRMET)
• AIRMET Sierra
• AIRMET Tango
• AIRMET Zulu
• Significant Meteorological Information (SIGMET)
• Convective Significant Meteorological Information (Convective SIGMET)
• Graphical Airmen’s Meteorological Information (G-AIRMET)
• Winds and Temperature Aloft Forecast (FB)
• Analysis
• Surface Analysis Chart
• Low Level Significant Weather Chart
• WEATHER THEORY
• Atmosphere
• Atmosphere Composition
• Layers of the Atmosphere
• Circulation Pattern on a Static Environment
• Coriolis Force
• Standard Pressure and Temperature
• Standard Pressure at Sea Level
• Standard Temperature at Sea Level
• Pressure Systems & Atmospheric Stability
• High Pressure System - Stable Atmosphere - Anticyclonic Circulation
• Low Pressure System - Unstable Atmosphere - Cyclonic Circulation
• How understand the movement of the pressure systems can be favorable for the flight
• Adiabatic Process
• Adiabatic Lapse Rate
• Dry Adiabatic Lapse Rate
• Moist Adiabatic Lapse Rate
• Convective Current
• Sea Breeze - Day
• Land Breeze - Night
• Unequal Heating
• Man Made Obstructions
• Mountainous Areas
• Turbulence
• Clear Air Turbulence (CAT)
• Thermal Turbulence
• Mechanical Turbulence
• Wake Turbulence
• Windshear (silent danger to aviation)
• Low Level Windshear
• Microburst
• Intensity
• Humidity and Relative Humidity
• Temperature
• Dew Point
• Clouds
• Determining Cloud Bases
• Ceilings
• Fog
• Radiation Fog
• Advection Fog
• Upslope Fog
• Steam Fog
• Ice Fog
• Air Masses
• Fronts
• Fronts Depiction
• Cold Front
• Warm Front
• Stationary Front
• Occluded Front
• Thunderstorms
• Cumulus Stage
• Mature Stage
• Dissipating Stage
• Direction of Movement of a Thunderstorm
• Squall Lines
• Tornadoes
• Icing
• Clear Ice
• Rime Ice
• Mixed

Intro

What Creates The Weather?

Uneven heat of the earth and moisture

Importance of the Weather in Aviation

Tell your own story, mine was from KEYW to KTMB

WEATHER SERVICES

Is a group of products where pilots or who concern are able to look different type of information regarding weather

Flight Service Station (FSS)

• The FSS is the primary source for preflight weather information.
• A preflight weather briefing from an FSS can be obtained 24 hours a day by calling 1-800-WX BRIEF from anywhere in the United States and Puerto Rico.
• Telephone numbers for FSS can be found in the Chart Supplement U.S. (formerly Airport/Facility Directory) or in the United States Government section of the telephone book.
• The FSS also provides in-flight weather briefing services and weather advisories to flights within the FSS area of responsibility.

Weather Briefings 1-800-WX-BRIEF

Pilots should always contact FSS to get a weather briefing prior to any flight (especially cross country flights).

• There are three different types of briefing a pilot can request.
• Standard Briefing
• Abbreviated Briefing
• Outlook Briefing

Weather Briefing Format

Standard WX Briefing Format.pdf

drive.google.com

1800WXBRIEF.COM

Flight Service

www.1800wxbrief.com

Web Page for Weather Information

AWC - Aviation Weather Center

Aviation Weather Overview Turns off interactive maps on main pages and adds a link to the interactive maps on a secondary page. Turning off maps is recommended for slow browsers and network connections. Aviation Weather Center Mission Statement: The Aviation Weather Center delivers consistent, timely and accurate weather information for the world airspace system.

www.aviationweather.gov

Types Of Aviation Weather Products

1. Observations
2. Forecasts
3. Analyses

Observations

Aviation Routine Weather Report (METAR)

• Is an observation of current surface weather reported in a standard international format.

METAR Brakedown

Reportable Contractions for Sky Conditions

METAR Notation for Reporting Present Weather

Special Weather Report (SPECI)

⚠️

Issued: When Needed

🏁

Valid For: 1 hour

• A SPECI is an unscheduled report taken when any of the criteria given in Table 3-1, SPECI Criteria, are observed during the period between hourly reports.
• SPECIs contain all data elements found in a METAR.
• All SPECIs are issued as soon as possible when relevant criteria are observed.
• Whenever SPECI criteria are met at the time of the routine METAR, a METAR is issued.

Pilot Weather Report (PIREPs)

The Best Source of Weather Information

⚠️

Issued: After receiving a report from a pilot

• Provide valuable information regarding the conditions as they actually exist in the air.
• Pilots can confirm:
• Height of bases and tops of clouds
• Locations of wind shear, turbulence and inflight icing.
• If the ceiling is below 5,000 feet, or visibility is at or below five miles, ATC facilities are required to solicit PIREPs from pilots in the area.

‣

UUA urgent pilot report contain information about:

Forecasts

Terminal Aerodrome Forecast (TAF)

Forecast of expected weather for a 5SM radius around an airport

• When visibility more than 6 SM, no significant weather phenomena and no clouds below 5,000ft,
• Will be reported as CAVOK (Ceilings and Visibility OK)

Graphical Forecast of Aviation Overview (GFA)

Provide the necessary aviation weather information to give users a complete picture of the weather that may impact flight.

⚠️

Issued: Hourly to 18 hours in the future,

• Includes:
• Observational data
• Forecasts
• Warnings including:
• Thunderstorms
• Clouds
• Flight category
• Precipitation
• Icing
• Turbulence
• Wind.

Coverage Area

GFA Tutorial Video

Airmen’s Meteorological Information (AIRMET)

Potentially Hazardous Weather for General Aviation

Significant Meteorological Information (SIGMET)

Potentially Hazardous to all Aircraft

• Report Weather Forecast that include:
• Severe Icing not associated with thunderstorms (SEV TURB)
• Severe or Grater Turbulence or Clear Air Turbulence CAT not Associated with thunderstorms (SEV ICE)
• Dust storms or Sandstorms that lower surface or in-flight visibilities to below 3 miles (WDSPR DS)(WDSPR SS)
• Volcanic Ash (VA)

Convective Significant Meteorological Information (Convective SIGMET)

Issued for Hazardous Convective Weather that affects safety of every flight. Are SIGMETs associated with Thunderstorms

• Convective SIGMETs are issued for severe thunderstorms with:
• Surface winds greater than 50 knots
• Hail at the surface greater than or equal to 3⁄4 inch in diameter
• Tornadoes

Graphical Airmen’s Meteorological Information (G-AIRMET)

Winds and Temperature Aloft Forecast (FB)

Computer-prepared forecasts of wind direction, wind speed, and temperature at specified times, altitudes, and locations.

Analysis

Surface Analysis Chart

Shows most recent observation of what is going on at the VALID time. (location of frontal lines and types of fronts)

⚠️

Issued: every 3 hours, 8 times a day

🏁

Valid For: The time is issued

Low Level Significant Weather Chart

Is a forecast of aviation weather hazards, primarily intended to be used as a guidance product for briefing the VFR pilot.

• Show:
• Visibility
• Ceilings
• Turbulence
• Freezing levels

WEATHER THEORY

Atmosphere

Atmosphere Composition

Layers of the Atmosphere

• The mayor percentage of the weather is located in the troposphere
• The tropopause is the layer between the Troposphere and the Stratosphere
• Most Jet streams and clear air turbulence are located here

Circulation Pattern on a Static Environment

• Air circulates around the globe as seen in the diagram pictured. This is because, as warm air rises (around the equator) the molecules spread apart. As this air expands, it becomes less dense and lighter than the surrounding air. Then, as the air cools, the molecules pack together more closes becoming heavier and denser than warm air. As a result, cool, heavy air tends to sink and replace warmer rising air.

Coriolis Force

• This circulation pattern causes the air to break up into three distinct cells in both the Northern and Southern Hemispheres. In the Northern Hemisphere (due to the rotational velocity of the Earth) the air is deflected to the right. In the Southern Hemisphere the air is deflected to the left. This deflection is called Coriolis Force.

Standard Pressure and Temperature

Pressure Systems & Atmospheric Stability

How understand the movement of the pressure systems can be favorable for the flight

Adiabatic Process

• The adiabatic process takes place in all upward and downward moving air.

1. When air rises into an area of lower pressure, it expands to a larger volume.
2. As the molecules of air expand, the temperature of the air lowers.
3. As a result, when a parcel of air rises, pressure decreases, volume increases, and temperature decreases.
4. When air descends, the opposite is true.

• The rate at which temperature decreases with an increase in altitude is referred to as its lapse rate.

Adiabatic Lapse Rate

• Since water vapor is lighter than air, moisture decreases air density, causing it to rise. Since moist air cools at a slower rate than dry air, it is generally less stable since the moist air must rise higher before its temperature cools to that of the surrounding air.

Convective Current

• Convection is vertically moving air where wind is horizontally moving air.
• Uneven heating of the Earth’s surface or man made objects can create areas of convection.
• This convection causes the “bumpy”, light turbulent sometimes experienced when flying at lower altitudes during warmer weather.

Sea Breeze - Day

• Ground, Rocks and Sand absorb solar energy quickly
• Water, Trees, and other areas of vegetation tend to more slowly absorb heat

Land Breeze - Night

• Ground, Rocks and Sand get cooler quickly
• Water, Trees, and other areas of vegetation tend to more slowly cool down

Unequal Heating

Man Made Obstructions

Mountainous Areas

• While the wind flows smoothly up the windward side of the mountain and the upward currents help to carry an aircraft over the peak of the mountain, the wind on the leeward side does not act in a similar manner. As the air flows down the leeward side it follows the contour of the terrain and becomes increasingly turbulent.

Turbulence

Clear Air Turbulence (CAT)

We cannot see it

Cause by

• Jet Streams
• Change in direction of the wind

How to avoid?

• Fly higher or lower

Thermal Turbulence

We can see it

Cause by

• Rising warm air (Thermals)

Mechanical Turbulence

Caused By

• Trees
• Hangars
• Buildings
• Rocky Mountains

Wake Turbulence

Caused by

• Wing Tip Vortex

Windshear (silent danger to aviation)

AC 00-54 Pilot Windshear Guide

www.faa.gov

www.faa.gov

• Windshear is a sudden, drastic change in wind velocity or direction or both.
• Windshear can subject an aircraft to violent updrafts and downdrafts, as well as abrupt changes to the horizontal movement of the airplane.
• Can occur at any altitude

Low Level Windshear

• Low level windshear is especially hazardous due to the proximity of the aircraft to the surface. Pilots should avoid low level windshear whenever it is known or has been reported.

Microburst

• These are the most severe type of low level windshear.
• They are typically associated with convective precipitation into dry air at a cloud base.
• They are indicated by intense rain shafts at the base of the cloud.
• It is essential that pilots avoid microbursts.

Intensity

• Horizontal diameter of 1-2 miles and a nominal depth of 1,000 feet
• Microbursts have a lifespan of about 5-15 minutes.
• During that time they can produce downdrafts up to 6,000 FPM and headwind losses from 30-90 knots.

Humidity and Relative Humidity

• Humidity refers to the amount of water vapor present in the atmosphere at a given time.
• Relative humidity is the actual amount of moisture in the air compared to the total amount of moisture the air could hold at that temperature.
• For example, if the current relative humidity is 65 percent, the air is holding 65 percent of the total amount of moisture that it is capable of holding at that temperature and pressure.

Clouds

• Clouds are visible indicators and are often indicative of future weather.
• For clouds to form, there must be adequate water vapor and condensation nuclei, as well as a method by which the air can be cooled. When the air cools and reaches its saturation point, the invisible water vapor changes into a visible state.

• Cumulus—heaped or piled clouds
• Stratus—formed in layers
• Cirrus—ringlets, fibrous clouds, also high level clouds above 20,000 feet
• Castellanus—common base with separate vertical development, castle-like
• Lenticularus—lens-shaped, formed over mountains in strong winds
• Nimbus—rain-bearing clouds
• Fracto—ragged or broken
• Alto—middle level clouds existing at 5,000 to 20,000 feet

Determining Cloud Bases

• Divide the temperature dewpoint spread by the convergence rate of 4.4 °F (2.5C), and multiply by 1,000 to determine the approximate height of the cloud base.

Ceilings

• For aviation purposes, Ceiling is the lowest layer of clouds reported as being BROKEN or OVERCAST
• VFR or VMC:
• Ceilings: grater than 3,000 ft AGL
• Visibility: Grater than 5 SM
• Marginal VFR - MVFR
• Ceilings: Between 1,000ft - 3,000ft AGL
• Visibility: Between 3 SM - 5 SM
• IFR or IMC:
• Ceilings: Below 1,000ft
• Visibility: Less than 3 SM

Fog

Fog Safety Overview

Fog, particularly when dense, can be hazardous to drivers, mariners and aviators. Fog contributes to numerous travel accidents every year. Restrictions in visibility resulting from fog can also impact takeoff and landing procedures and requirements for pilots, and can be the cause of weather-related aviation delays.

www.weather.gov

• Fog is a very low cloud that is on the surface.
• It typically occurs when the temperature of air near the ground is cooled to the air’s dew point.
• At this point, water vapor in the air condenses and becomes visible in the form of fog.
• Fog is classified according to the manner in which it forms and is dependent upon the current temperature and the amount of water vapor in the air.

Radiation Fog

• After a clear of clouds, winds calm and cool night, the ground get really cold radiating that low temperature to the air that is moving over, decreasing the air temperature until reaching the dew point
• Usually in low areas like mountain valleys

Advection Fog

• Forms when a layer of warm, moist air moves over a cold surface and cools to its dewpoint.
• Wind is required for Advection Fog to develop – up to 15 knots. Above 15 knot winds the fog lifts and forms low stratus clouds.
• Usually found in the costal areas with sea breezes

Upslope Fog

• Forms when moist, stable air is forced up sloping land features like hills and mountain ranges.
• This type of fog also requires wind to develop.
• It may not burn off with the morning sun and can persist for days.
• Usually around sloping terrain like mountain ranges

Steam Fog

• Forms when cold, dry air moves over relatively warm water.
• As the water evaporates, it rises and resembles smoke.
• That’s why this type of fog is also referred to as “Sea Smoke.”
• Usually over cold water on winter

Ice Fog

• Forms in very cold weather when the temperature is much below freezing (-25F or colder).
• This occurs because the water vapor in the air is directly forming into ice crystals.
• Usually in Artic regions or in very cold temperatures

Air Masses

• Air masses are classified according to the regions where they originate. They are large bodies of air that take on the characteristics of the surrounding area or source region. A source region is typically an area in which the air remains relatively stagnant for a period of days or longer. During this time of stagnation, the air mass takes on the temperature and moisture characteristics of the source region.

Fronts

As an air mass moves across bodies of water and land, it eventually comes in contact with another air mass with different characteristics. The boundary layer between two types of air masses is known as a front. There are four types of fronts:

1. Warm
2. Cold
3. Stationary
4. Occluded

Fronts Depiction

Cold Front

• Move rapidly, typically 25 to 30 (Max 60) miles per hour
• Cumulonimbus and towering cumulus clouds
• Violent weather activities, storms, gusty winds, turbulence, hail or tornadoes

Warm Front

• Move slowly, typically 10 to 25 miles per hour
• Stratiform clouds
• Low ceilings, poor visibility and rain

Stationary Front

• When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days.
• The weather associated with a stationary front is typically a mixture that can be found in both warm and cold fronts.

Occluded Front

• An occluded front occurs when a fast- moving cold front catches up with a slow- moving warm front.
• As the occluded front approaches, warm front weather prevails but is immediately followed by cold front weather.

Thunderstorms

• 3 Factors must meet in order to create a thunderstorm
1. High Moisture
2. Unstable Air
3. Vertical Development
• Almost impossible to fly over thunderstorms in light aircraft because can get high up to 60.000 feet
• Flying under thunderstorms can subject aircraft to rain, hail, damaging lightning, and violent turbulence.
• A good rule of thumb is to circumnavigate thunderstorms identified as severe or giving an extreme radar echo by at least 20 NM since hail may fall for miles of the clouds
• If flying around a thunderstorm is not an option, stay on the ground until it passes.

Direction of Movement of a Thunderstorm

Squall Lines

• A squall line is a narrow band of active thunderstorms.
• Often it develops on or ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front.
• The line may be too long to detour easily and too wide and severe to penetrate.
• It often contains steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Tornadoes

• If the incoming air has any initial rotating motion, it often forms an extremely concentrated vortex from the surface well into the cloud.
• Meteorologists have estimated that wind in such a vortex can exceed 200 knots with pressure inside the vortex quite low.
• The strong winds gather dust and debris and the low pressure generates a funnel-shaped cloud extending downward from the cumulonimbus base.
• If the cloud does not reach the surface, it is a funnel cloud; if it touches a land surface, it is a tornado; and if it touches water, it is a “waterspout.”

Icing

• Icing can quickly affect aircraft in flight by disturbing the smooth airflow over the wings, propeller, and tail. It should be avoided whenever possible (even if the aircraft is approved for flight into known icing conditions).

Clear Ice

• Clear in color
• Develops from large water droplets
• Freezes as it runs back along the wing surface

Rime Ice

• Milky in color
• Develops from smaller water droplet
• Freeze on impact with the wing

Mixed

• This is a mixture of both Clear and Rime Ice