Upper air, radar & air-reports

What does an upper-air sounding measure?

A vertical profile is assembled over an ascent, not captured everywhere at one instant.

Sensors, telemetry and position

A radiosonde is an instrument package carried by an ascending balloon. It measures temperature and humidity, and pressure is measured or derived using the system’s height and atmospheric processing. Position tracking, commonly GNSS, gives movement from which horizontal wind speed and direction are derived. Measurements are transmitted by radio to a receiving station and quality-controlled into a profile.

Pressure generally decreases as the balloon rises. The balloon also drifts with the wind, so the higher measurements may be many kilometres from the release point and were observed later than the lower measurements. The profile is not an instantaneous vertical column fixed over the launch station. A routine network often samples near standard synoptic times, with additional soundings where arranged; it does not observe every valley or every convective change continuously.

The profiles initialise and verify numerical forecasts, identify stable layers and inversions, locate freezing levels and moist layers, and describe upper winds and tropopause structure. Humidity sensors can have response or icing limitations and radiation affects temperature sensing. Use launch time, path, data quality and neighbouring information before applying one sounding to a distant route.

Where are the moist layer, inversion and freezing level?

Start with the axes and the temperature/dew-point traces.

A simplified T–P diagram

Pressure is the vertical coordinate and decreases upwards; temperature is the horizontal coordinate. A simplified rectangular diagram is not necessarily a skew-T, and logarithmic pressure spacing is common in operational thermodynamic charts. Read the diagram’s own axes rather than assuming equal pressure intervals equal equal height intervals. Identify environmental temperature T, dew point Td and any plotted wind barbs.

A close T–Td spacing suggests high relative humidity and possible cloud; a wide spacing suggests drier air. It does not prove an exact cloud boundary because saturation reference, instrument response, resolution and local variability matter. An inversion is a layer in which environmental T increases as pressure falls upwards; an isothermal layer has little T change. Find all crossings of the 0 °C isotherm: a warm nose can give several freezing levels, with consequences for melting, refreezing and supercooled liquid.

Use the environmental slope and an appropriate parcel path to assess stability. A warm layer over a cold moist surface layer can cap convection and preserve low cloud. A sounding with steep lapse rates, low-level moisture and ascent can support deeper convection, but a profile alone does not provide the required trigger everywhere. Wind changes with level add shear; high wind on one level alone does not quantify turbulence.

Does a bright pixel mean a high cold cloud?

Visible reflectance, thermal emission and water-vapour absorption describe different features.

Observation platform and radiation

Meteorological satellites carry radiometers that measure radiation in selected spectral bands. Geostationary satellites remain over approximately the same equatorial longitude and provide frequent views of a large disc; viewing geometry deteriorates towards high latitudes and the limb. Low Earth/polar-orbiting satellites scan changing swaths, providing broad global coverage including polar regions, with different revisit and spatial-resolution characteristics. Neither supplies an uninterrupted detailed three-dimensional view everywhere.

Visible imagery mainly displays reflected sunlight: thick bright cloud often contrasts with darker sea, but snow, ice, sand and sun angle can confuse it. Texture and shadows help distinguish cloud forms in daylight. Conventional visible reflectance is unavailable at night; specialised low-light sensors are a separate capability. Infrared window imagery measures emitted radiance expressed as a brightness temperature and is useful day or night. High opaque tops are commonly colder than lower cloud, but thin cirrus, inversions and warm low cloud complicate a direct temperature-to-height inference.

Water-vapour channels are sensitive to moisture and temperature over a broad, channel-dependent atmospheric layer, often the middle/upper troposphere. They help locate dry intrusions, moist plumes and circulation patterns; a dark dry upper-air region does not guarantee a cloud-free or fog-free surface. Multispectral RGB products combine channels to distinguish features such as dust, ash, phase or low cloud, subject to product legends and limitations. Colours in an enhanced product are not necessarily natural visible colours.

How do cloud patterns help locate a front?

Infer a weather structure with other data rather than drawing a surface front on every bright boundary.

Cumuliform versus stratiform patterns

Stratiform cloud often makes broad smoother sheets or bands; cumuliform cloud commonly has cellular, lumpy or textured patterns, sometimes with shadows or anvils in visible imagery. Shallow convection may show open or closed cells behind a cold front, while deep convection produces cold expanding anvils. High cirrus can hide low cloud, and a smooth-looking anvil is not proof of stable harmless air underneath. Infrared temperature, visible texture and successive frames should be compared.

A mid-latitude frontal system may show an elongated cloud band, a broad warm-conveyor shield, a comma head and a dry intrusion. A warm front often has extensive layered cloud ahead of the surface boundary; a cold-frontal band may be narrower and convective, but actual structures vary. The surface front need not coincide with the outer edge of high cloud: the sloping surface and wind aloft displace cloud away from the ground boundary.

Locate cloud organisation and its evolution, then combine surface pressure, temperature/dew-point changes, wind, radar and analysis charts to assess the front and route conditions. Use the imagery timestamp and any animation interval. A cellular region can suggest showers and turbulence exposure, and a cold broad shield can conceal embedded convection; imagery alone does not establish cloud base, RVR, liquid-water amount or a clear gap at flight level.

How can satellite motion vectors reveal a jet?

A displacement becomes a useful wind only when the feature and representative height are known.

Atmospheric motion vectors

Atmospheric motion vectors are derived by tracking suitable cloud or water-vapour patterns through sequential images, dividing their displacement by elapsed time and assigning a representative pressure/height with radiative and atmospheric information. Direction and speed describe the motion attributed to that tracer; they are not a direct wind measurement at every point and every level.

High-level vectors can reveal a ribbon of strong flow, its curvature and jet-axis location when examined with their assigned levels and quality flags. A dense band of fast vectors around 250–300 hPa can support a jet diagnosis, while slow low-cloud vectors beneath it describe a different layer. Compare with upper-air analyses, water-vapour structure and forecast isotachs. Track changes in space and time, rather than treating a single fast vector as the whole jet.

Height-assignment error, thin or multilayer cloud, feature growth and tracking ambiguity can bias the result. A moisture pattern can evolve rather than move as a passive tracer. A jet may also occur where few suitable tracers exist; no vectors do not mean no wind. An AMV image helps locate the wind structure, but does not prove the position or severity of clear-air turbulence.

Interpret an original atmospheric-motion-vector field

Open page 2 of the linked NOAA Derived Motion Winds guide. In the archived 1802 UTC 12 February 2018 field, white/grey barbs represent 250–350 hPa tracers, blue/cyan 450–550 hPa, and red/pink 800–900 hPa. Read the layer key before comparing arrows. The concentrated upper-level flow follows the eastern United States towards the North Atlantic; it is the upper-jet signature, whereas the low-level circulation over the Atlantic belongs to a different layer.

Compare the upper and lower vectors at matching positions to identify vertical wind change, while preserving each tracer’s assigned level. The mid-level ridge over the northern Plains is another feature. Neither the density of barbs nor one colour alone gives a CAT severity. This is an archived retrieval display, not current wind or a forecast. The displacement model above isolates the calculation; the original field below its link supplies the spatial interpretation.

What does a strong radar echo actually indicate?

A radar image shows sampled backscatter, not a photographic cloud outline.

Range, reflectivity and velocity

A weather radar transmits electromagnetic pulses and receives backscatter from targets. The return delay gives distance, range = light speed × round-trip time / 2; antenna direction and elevation locate the sampled volume. Reflectivity describes returned power related to particle number, size, phase and dielectric properties. Strong reflectivity often marks heavy liquid precipitation or hail, but it is not a direct universal rainfall or turbulence intensity measurement.

A ground radar scans elevations to build products such as a low-elevation reflectivity image or a composite of maxima aloft. Doppler processing measures the component of scatterer motion towards or away from the radar, not the full horizontal wind vector at every pixel. Dual-polarisation information helps distinguish target properties and improve precipitation estimates. Product definitions and legends determine what a displayed colour means.

Read timestamp, scan type, range and units before interpreting cells, bands, holes or growth. Curvature/refraction and antenna elevation raise the beam above the surface with distance; the beam widens and can overshoot shallow precipitation or merge small cells. Terrain blockage, ground/sea clutter, anomalous propagation, bright-band enhancement near melting, attenuation and processing can create false echoes or conceal real precipitation. A composite maximum may show precipitation above an aircraft rather than at its level. Mosaics add latency and combine scans from different times; a gap is not a guaranteed current corridor.

Is a black region beyond a red echo clear?

Use the specific aircraft system’s modes, tilt and attenuation indications.

Airborne weather radar

Airborne weather radar uses the same pulse/backscatter principle with a stabilised antenna or electronic scanning system. Conventional precipitation modes mainly reveal liquid precipitation and suitably reflecting particles in the sampled volume. They do not directly outline all cloud, supercooled droplets, ice-crystal regions, volcanic ash or clear-air turbulence. Some systems have turbulence and predictive wind-shear functions with specified targets and operating ranges; these capabilities cannot be assumed for every radar or mode.

Tilt determines which heights are illuminated. An excessively high beam can pass through weakly reflecting upper ice or above a low cell, while low tilt can produce ground returns. The beam widens with range; the displayed return is not a sharply bounded point at the aircraft level. Automatic volumetric radars manage some scans differently, so interpret their altitude filters, gain and symbols through the aircraft documentation.

Heavy precipitation can attenuate the outgoing and returning energy, leaving a weak/black shadow behind a strong leading echo. A wet/contaminated radome, range, blocked sectors, settings and target phase also affect detection. Weak upper ice returns can coexist with dangerous convection or HIWC; a missing echo is not proof of no hazard. Compare successive scans, appropriate tilt/range views and attenuation warnings. Recognise severe gradients, organised lines and rapid growth as reasons to preserve avoidance space, not to seek a minimum-colour tunnel. Use aircraft/operator clearance criteria and coordinate a safe route early.

Interpret original airborne-radar displays

In figure 5 of the linked Airbus article, black wedge-shaped sectors extend beyond the stronger nearer returns. The display illustrates attenuation: energy may be insufficient to reveal what lies farther away. Treat those sectors as uncertain, rather than selecting them as clear passages.

In figure 10, this particular RDR-4000 depiction uses solid colours for returns within the selected flight-path envelope and stripes for secondary returns outside that envelope. Striped weather is not thereby absent or universally safe; changing the path can make it relevant. Interpret the mode and altitude context, then compare the vertical structure. These are manufacturer-specific examples, not a legend for every radar. The source article’s 2016 technology descriptions do not establish what equipment is installed on a present aircraft.

What belongs in a special air-report?

A report needs the event’s time, position and level, not just a description of discomfort.

Routine and event-driven reporting

A routine air-report supplies scheduled meteorological observations during en-route/climb phases through the applicable automatic/data-link arrangements, including wind and temperature and other available elements. It contributes direct samples to analysis and forecasting. A special air-report, identified as ARS in coded dissemination, is triggered by specified significant conditions; it is not delayed until the next routine observation time.

Under SERA, special and other non-routine observations apply during any flight phase. Where voice is used for a special report, give the aircraft identification, position, UTC time, level or level range and the condition prompting it, with relevant intensity and operational details. Use the standard reporting format and phraseology, not an invented weather code. Transmit at the observation time or as soon as practicable with aircraft control and immediate safety priorities maintained. When air-ground data link is unavailable or unsuitable, use the appropriate ATS voice channel for these event reports.

Routine automatic reporting arrangements do not remove the obligation to report a significant encounter. Conversely, do not import an old requirement for every aircraft to make routine meteorological voice reports at fixed intervals: the present routine data-link framework and published local arrangements must be distinguished from special/other non-routine reports. A pilot report is a point/path sample affected by aircraft type, speed, response and time, so include enough context for another aircraft or forecaster to apply it.

Does SERA require severe intensity for every phenomenon?

Read the qualifiers: they differ between turbulence, icing, waves and thunderstorms.

SERA triggers and other safety-relevant observations

The SERA special-observation list includes moderate or severe turbulence; moderate or severe icing; severe mountain wave; thunderstorms with or without hail when obscured, embedded, widespread or in squall lines; heavy duststorm or sandstorm; volcanic ash cloud; pre-eruption volcanic activity or an eruption; and runway braking action encountered which is not as good as reported. The thunderstorm qualifiers and the different intensity thresholds matter. It would be wrong to wait for severe icing before reporting a moderate encounter.

Other meteorological conditions, such as wind shear, which in the pilot-in-command’s opinion may affect safety or markedly affect the efficiency of other aircraft operations are also advised to the appropriate ATS unit as soon as practicable. A phenomenon need not appear as the exact name of a SIGMET to be operationally useful or reportable. ATS relays relevant reports to other aircraft, the meteorological service and, for inconsistent runway braking reports, the aerodrome operator as applicable.

Separate what was actually observed from an inference. Report the location and level range of icing, the encountered intensity, or the specific ash/volcanic evidence; do not claim a whole FIR has the same state. Braking action is an aircraft encounter assessment and is not a pilot’s new runway condition code for all runway thirds. A report that conditions are worse than the published information should trigger reassessment, not automatic reliance on the older value.

What changes when the observation time stays the same but the channel changes?

Compare the original NOAA/Aviation Weather Center images for 1636 UTC, 19 July 2019. These U.S. examples teach sensing physics; they are archived observations, not current route information.

Start with the header and each legend

All three images have the same observation time and geographic view. The visible image has a grey reflectance scale: brightness concerns reflected sunlight, not a cloud-top temperature. In this scene, a bright structured cloud shield lies across the northern central United States, while a broad low-cloud sheet and cellular patterns lie over the Pacific west of California. Use texture and the coastlines to compare the same locations; do not assume every bright area has the same cloud height.

The enhanced infrared legend is in degrees Celsius. In this particular palette, blue/purple represents colder brightness temperatures and orange/red represents warmer ones. The cold compact upper-cloud areas over the northern central states are prominent, while some bright Pacific cloud in the visible view is much less cold in the infrared view. That contrast supports a lower/warmer cloud interpretation for the Pacific sheet relative to the cold upper shields; it does not alone measure cloud base, geometric top height, precipitation phase or turbulence. Red here means warm brightness temperature, not severe radar precipitation.

The water-vapour image has its own temperature legend, approximately −69 to −11 °C. It is not a relative-humidity percentage scale. The dry-looking orange/brown band west of California and dry upper-air sectors farther east describe channel-weighted atmospheric conditions; compare the visible image before making any claim about low cloud below. Bright/cold convective shields also affect the water-vapour view. No one channel supplies runway visibility or a complete three-dimensional hazard map.

One instant cannot give a motion vector

These are three channels at one time, not three successive times. They cannot yield a cloud displacement speed. A motion estimate requires a later image in an appropriate channel, a reliable scale and interval, tracer matching and representative height assignment. Nor should a surface warm or cold front be placed exactly on a high-cloud edge without the surface analysis.

Does a coloured return establish precipitation at the aircraft level?

Read the archived National Weather Service WSR-88D composite-reflectivity example from 27 June 2019, 1153 UTC. It is neither a current warning nor an aircraft radar display.

Product, time, location and units before colour

The header identifies the National Weather Service WSR-88D image and its observation time. The handbook identifies the product as composite reflectivity: the maximum sampled reflectivity in each vertical column, assembled from the radar volume scan. The right-hand scale is dBZ. Its colours describe reflectivity bins, not a direct label for turbulence, a cloud base or a guaranteed rainfall rate at the surface.

Locate the stronger yellow/orange/red returns near the Poplar Bluff–Sikeston–Dyersburg area and compare them with the weaker cyan/green area near Memphis. The stronger returns indicate more powerful sampled backscatter somewhere within the product column; particle size, number and phase matter. This alone does not prove a tornado, hail size, a specific cloud genus or severe turbulence at every level underneath. The coloured warning-category labels along the bottom are part of the original archived display and must not be read as warnings in force now.

For an aircraft-level decision, obtain product height/scan information, current evolution and other evidence. A composite can contain a strong echo aloft above a weaker lower layer, while a low-elevation beam can overshoot shallow distant precipitation or be blocked. The missing echo is therefore a sampling question before it is a route opportunity. Do not use this ground-radar product as if it were the aircraft’s current forward-looking scan.

Can you apply the ideas?

Four original questions. Decide from the facts, then review the explanation.