Present Weather Flashcards
What is Present Weather?
Weather occurring at the time of observation on or over the aerodrome. Weather may be reported as ‘in the vicinity’ (VC) if it occurs within 8km of the aerodrome but not on the aerodrome itself.
What is the reporting order of weather phenomena?
Precipitation -> Obscuration -> Other
How many characters can the present weather group contain?
A maximum of 9 characters.
How many groups may be inserted to report the present weather?
Up to 3 groups can be inserted to report simultaneously occurring independent phenomena.
How are simultaneous but different forms of precipitation reported?
They should be reported as one single group in order of dominance (e.g RADZ).
Name the descriptor codes
- MI - Shallow (Marshmallow)
- BC - Patches (Batches)
- PR - Partial
- DR - Low Drifting
- BL - Blowing
- SH - Showers
- TS - Thunderstorm
- FZ - Freezing
Name the precipitation codes
- DZ - Drizzle
- RA - Rain
- SN - Snow
- SG - Snow Grains
- PL - Ice Pellets
- GR - Hail (Grail)
- GS - Small Hail/Snow Pellet (Grail Small)
Name the obscuration codes
- BR - Mist (Brist)
- FG - Fog
- FU - Smoke (Fumer)
- VA - Volcanic Ash
- DU - Dust
- SA - Sand
- HZ - Haze
Name the Other codes.
- PO - Dust/Sand Whirls or Dust Devil (O is a whirl)
- SQ - Squalls
- FC - Funnel cloud or water spout
- DS - Dust Storm
- SS - Sandstorm
What is BL?
Blowing. A descriptor used to indicate dust, sand or snow that has been raised by the wind to a height of 2m or more.
What is DZ?
Drizzle. Uniform precipitation of very fine drops of water that have a diameter of less than 0.5mm. Generally the heavier the drizzle, the lower the cloud base and the worse the visibility.
What is DU?
Dust. A widespread suspension of small particles of dust raised from the ground. As this is in obscuration, it is only reported when the vis is 5000m or less. Rarely reported in the UK.
What is PO?
Dust/Sand Whirls or Dust Devil. A near vertical and rapidly rotating column of air, forming a dust/sand whirl. Dust Devils are usually only a few metres in diameter and extend no higher than 200-300ft. Rarely reported in the UK.
What is FG?
Fog. A suspension of very small water droplets (or ice crystals) in air, when the visibility is less than 1000m in all directions and the relative humidity is 100%. The temperature and dewpoint are usually the same or very similar.
What is FZ?
Freezing. A descriptor used when it is necessary to indicate the water droplets in fog, drizzle or rain are in a supercooled state.
What is FC?
Funnel Cloud (Tornado). Rotating column of air, often a violent whirlwind, indicated by the presence of an inverted cone-shaped cloud. A funnel cloud that touches the surface is described as ‘well-developed’ and the ‘+’ descriptor is used. Rarely reported in the UK.
What is GR?
Hail (Grail). Balls of ice with a diameter 5mm or more, falling from deep cumuliform cloud that contains vigorous updrafts.
What is GS?
Small Hail (Grail Small). Balls of ice with a diameter 5mm or less, falling from deep cumuliform cloud that contains vigorous updrafts.
What is HZ?
Haze. A widespread amount of small dry particles in the air. As it is an obscuration it shall be reported when the visibility is 5000m or less and and the relative humidity is less than 95%. The difference between the temperature and dewpoint is usually more than 1 degree.
What is PL?
Ice Pellets. Frozen raindrops, falling from deep stratiform cloud usually having a diameter of 5mm or less. Ice Pellets may occur before or after Freezing Rain and indicate that supercooled precipitation may be present at higher levels.
What is DR?
Low Drifting. A descriptor used to indicate dust, sand or snow that has been raised by the wind to a height of less than 2m.
What is BR?
Mist (Brist). A suspension of water particles in the air reported when the visibility is between 1000m and 5000m and the relative humidity is 95% or more. The difference between the temperature and dewpoint is usually 1 degree or less.
What is PR?
Partial. A descriptor used only with Fog to indicate that Fog, 2m or more deep covers a substantial part of the aerodrome, while the rest is clear.
What is BC?
Patches (Batches). A descriptor used only with Fog to indicate that Fog, 2m or more deep is present at the aerodrome but in irregularly distributed patches.
What is RA?
Rain. A precipitation of water droplets with a diameter of 0.5mm or more. If the precipitation is falling from cumuliform clouds, then it is described as a shower.
• Light ‘-‘ rain is precipitation of low intensity such that puddles form only slowly, if at all.
• Moderate rain is is precipitation of moderate intensity such that puddles form rapidly and some spray is seen on hard surfaces.
• Heavy ‘+’ rain is precipitation of high intensity which makes a roaring noise on roofs and forms a misty spray on hard surfaces.
In the UK, rain is 80% light, 15% moderate and only 5% heavy.
What is SA?
Sand. In the UK typically only reported in combination with DR or BL to indicate sand picked up by the wind.
What is MI?
Shallow (Marshmallow). A descriptor used only with Fog to indicate that Fog, whether patchy or continuous, is present on the airfield and less than 2m deep. As a result, the reported visibility is 1000m or more.
What is SH?
Shower. A descriptor used to identify precipitation falling from cumuliform cloud. Showers are short-lived and often characterised by their sudden beginning and ending.
What is FU?
Smoke (Fumer). As it is an obscuration it should be reported when the visibility is 5000m or less. It can be reported when the visibility is less than 1000m and the relative humidity is 90% or less.
What is SN?
Snow. Solid precipitation of snowflakes. Light is up to 0.5cm/hr, heavy over 4cm/hr and moderate is inbetween.
What is SG?
Snow Grains. The frozen equivalent of drizzle falling from stratus cloud or fog.
What is SQ?
Squall. A Strong wind that increases suddenly by at least 16 knots, increasing to 22 knots or mote and sustained for at least one minute before dying away. Distinguished from a gust by its longer duration. Typically occuring along the line of a cold front.
What is TS?
Thunderstorm. Associated with cumulonimbus clouds. When thunder is heard with no precipitation falling on the aerodrome TS alone is reported in the METAR, or VCTS if the source is estimated to be within 8km of the aerodrome boundary. To report with precipitation, TS is used as the descriptor. TS shall be reported if thunder is heard within 10 minutes preceding the observation.
What is VC?
In the Vicinity. Certain phenomena are reported as in the vicinity if they occur within 8km of the aerodrome. Only BL, SA, SN, FC, PO, FG, SH and TS can be reported VC. For VCSH and VCTS the precipitation type is not specified.
What are the 5 conditions that must exist simultaneously in order to report CAVOK?
- Prevailing visibility of 10km or more
- No minimum visibility reported
- No cloud below 5000ft or below the highest minimum sector altitude, whichever is greater,
- No towering cumulus or cumulonimbus clouds present
- No significant weather phenomena on or in the vicinty of the aerodrome
