Chapter 3

Chapter 3 - Weather #

Introduction #

  • atmospheric pressure
  • wind and currents
  • uneven surface heating
  • visibility and cloud clearance
  • precipitation
  • Convective currents when warm air rising
  • Urban areas give off more heat & are more likely to have updrafts

Questions #

  • Current weather conditions are an important consideration when evaluating unmanned aircraft performance.
  • Every physical process is accompanied by or result of heat exchange
  • Unequal heating in earth’s surface causes variations in altimeter settings between weather reporting points
  • Development of thermals depends on solar heating
    • Which area would have the most thermal current? 5, 7 or 2?::2
  • Clouds, fog, or dew will always form when water vapor condenses

Wind #

  • winds can affect flight time and stability
  • winds can create updraft near buildings and downdraft from over the buildings
  • flying low may create rapidly changing wind

Air Masses & Fronts #

  • air takes on properties it rests on or moves over.
    • :air mass modification
  • cold front is leading edge of cold air
    • poor weather ahead & passes quickly & wind shift
  • warm front leading edge of warm air
    • more heavy effect on weather & move half as fast as cold
  • ridge: high pressure
  • trough: low pressure

Atmospheric Stability #

  • stable atmosphere is resistant to vertical motion
  • stable layers of air is associated with temperature inversion

Questions #

  • Stable air mass has showery precipitation characteristic
  • Moist unstable airmass has haze and smoke
  • stable air has poor visibility and steady precipitation
  • actual lapse rate determines stability of atmosphere
  • Warming from below decreases stability
  • unstable air mass approaching, thunderstorms and turbulent conditions are concern
  • Low level temperature inversion & high relative humidity = :: smooth air, poor visibility, fog haze or low clouds

Visibility & Clouds #

  • 3SM visibility from control station
  • sUAS is kept 500feet below clouds & 2000 feet horizontally

Thunderstorms #

  • three requimrents
    • sufficient water vapr
    • sufficient lapse rate
    • initial upward boost
  • virga is water that evaporates before it hits the ground and should be avoided
  • avoid 20sm from storms because of turbulent conditions
  • the mature stage is the greatest intensity
  • thunderstorms draw in air from the middle creating a vortex
  • microburst is a intense small scale downdraft

Questions #

  • continuous updraft is associated with cumulus stage of thunderstorms
  • Precipitation falling is a sign of the beginning of the mature stage of a thunderstorm
  • High humidity, a lifting force, and unstable conditions are necessary for the formation of clouds
  • Dissipating stage is mostly downdrafts
  • Squall line thunderstorms produce the most intense hazard to aircraft
  • Nonfrontal narrow band of active thunderstorms ahead of a cold front is called the squall line
  • Wind shear is a hazard associated with all thunderstorms
  • Lightning and thunder is associated with thunderstorms
  • static electricity is a hazard when flying near thunderstorms
  • Duration of microburst is less than 15 minutes from when it strikes the ground
  • Squall is most likely to form at any altitude

Icing #

  • icing occurs when water is supercooled
  • any indication of icing the pilot should recover the sUAS immediately
  • visible moisture is necessary for structural icing to form

Questions #

  • presence of ice pellets at surface is evidence that there is freezing rain at higher altitude.
  • visible moisture is required for structural icing to form
  • frost will occur with dewpoint of surface below freezing & dewpoint is above freezing

Fog #

  • fog comes from water added to air near surface
  • fog requires low temperature/dew point spread
  • fog is more prevalent around industrial areas
  • many types of fog:
    • radiation
    • advection
    • upslope
    • precipitation induced
    • steam
  • Pilot must recover when <3SM visibility occurs

Questions #

Density Altitude #

  • sUAS performance will decrease with high temperature, marginally with high humidity, low atmospheric pressure, and altitude increase

Questions #

Weather Briefing #

Weather Reports, Forecasts, & Charts #

  • (ASOS) Automated Surface Observing System - primary weather observing
    • processes weather, minute by minute, computer transmitted
  • (AWOS) - marked by (AUTO)
  • Metar Report Example
  • METAR is standard international format - scheduled
    • METAR KGG 161753Z AUTO 14021G26KT 3/4SM +TSRA BR BKN008 OVC012CB 18/17 A2970 RMK PRESFR - TYPE : METAR OR SPECI - STATION Identifier : KGG - DATE & TIME (SIX DIGITS) : 161753Z - 16 = Date - 1753 = Time - Z = Zulu Time - Modifier : AUTO or COR (Corrected) - Wind : 14021KT (five digits or 6 if greater than 99 knots) - 140 = Direction true win is blowing in tens of degree - or VBR = variable - G for gusting - V to separate extreme wind direction - Visibility : 3/4SM - R/ = runway visibility - Weather : qualifiers & phenomena : +TSRA - - = HEAY - TS = THUNDERSTORMS - RA = RAIN - Sky Condition : amount, height, & type in that order : height is in hundreds of feet - BKN008 : Broken 800 feet - OVC012CB : Overcast 1,200 feet - VV003 : Vertically visible 300 feet - - Temperature & Dew Point in order : 18/17 - In Celsius, M if minus (M18/M17) - Altimeter settings : A2970 - inches of mercury (Hg) 4 digit number always A infront - PRESRR - RISING RAPIDLY - PRESFR - FALLING RAPIDLY - Zulu time - Remarks : RMK comments
      You can copy and paste a Metar report into ChatGPT and tell it to describe each section of the Metar Report.
ChatGPT Metar Report

The given text is a METAR report, which is a standard format used for reporting weather observations at airports. Here’s a breakdown of each section:

KTPA: This is the ICAO station code for the airport where the observation was taken. In this case, it refers to Tampa International Airport.

202353Z: This section provides the date and time of the observation. “20” represents the day of the month (20th), “2353Z” indicates the time in Coordinated Universal Time (UTC) when the observation was made, which is 23:53 UTC.

VRBO3KT: This part describes the wind conditions. “VRB” means the wind direction is variable and is not predominantly coming from a specific direction. “03KT” represents the wind speed, which is 3 knots.

10SM: This section denotes the visibility, indicating that the visibility is 10 statute miles, which is the maximum value reported.

SCTO50CB: This segment provides information about cloud coverage and types. “SCT” stands for scattered clouds. “O50CB” means there are towering cumulonimbus clouds with their bases at or below 50,000 feet above ground level (AGL).

SCT100: This part indicates the presence of scattered clouds at an altitude of 10,000 feet above ground level (AGL).

BKN250: This section represents broken clouds at an altitude of 25,000 feet above ground level (AGL).

28/22: This segment provides the temperature and dew point information. “28” refers to the air temperature in degrees Celsius, and “22” represents the dew point temperature in degrees Celsius.

A2996: This part indicates the atmospheric pressure at sea level, expressed in inches of mercury (inHg). In this case, the pressure is 29.96 inHg.

RMK: This section indicates remarks or additional information following the observation.

AO2: This is an automated weather station with a precipitation discriminator.

LTG DSNT NE AND E: This remark signifies that lightning is observed distant to the northeast and east of the observation site.

SLP144: This segment provides the sea-level pressure, which is 1014.4 millibars (hPa).

CB NE MOV S: This remark indicates cumulonimbus clouds are present in the northeast and moving south.

CB DSNT N-S: This remark indicates cumulonimbus clouds are present in the distance from the north to the south.

TCU DSNT W: This remark denotes towering cumulus clouds are present in the distance towards the west.

60072 T02780217 10344 20244 53002: These are additional weather observations, including wind direction and speed, temperature, dew point, and atmospheric pressure.

$: The dollar sign represents the end of the METAR report.

Overall, the METAR report provides detailed information about the weather conditions at the specified airport at the time of the observation.

  • TAF - another weather report usually given 4 times a day (0000Z 0600Z 1200Z 1800Z)
    • TAF KPIR 111130Z 1112/1212 15012KT P6SM BKN090 TEMPO 1112/1114 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM120000 14012KT P6SM BKN080 OVC150 PROB30 1200/1204 3SM TSRA BKN030CB FM120400 1408KT P6SM SCT040 OVC080 TEMPO 1204/1208 3SM TSRA OVC030CB
    • Type of report : TAF or TAF AMD
    • ICAO Station identifier : KPIR
    • Date & time of origin : 111130Z
    • Valid period dates & times : 1112/1212 first two being day & 2nd two are hour
      • 11th hour 12
      • 12th hour 12
    • Forecast wind : 15012KT
      • 150 = wind in true north
      • 12KT = 12 knots
      • or 120KT = 120KT
    • Forecast visibility : P6SM
      • in statue miles (P6SM means over 6 miles)
    • Forecast significant weather : BKN090
      • same format as METAR
    • Forecast sky condition
    • Forecast Change Group : TEMPO
      • TEMPO = Temporary within 1 hour
      • FM = Rapid & significant change within hour
    • PROB30 = given percentage of thunderstorms and precipitation in the coming hours

Questions #

  • what is true of ASOS/AWOS :: ASOS locations perform weather observing functions necessary to generate METAR reports