Weather Radar Interpretation
Intensity, tilt, attenuation and limitations; radar does not detect all hazards.
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Tilt the antenna (drag the cyan handle at the end of the beam in the side view, or use the slider) and watch the radar display. The side view shows why: the beam rises with distance over the curved earth and spreads with its width, so at 40 NM a 5° beam is about 3.5 NM tall. Where the beam meets the wet part of a storm, below the freezing level, the return is strongest; aimed over it, into the frozen top, the same storm looks weak or vanishes — overscanning. Aimed too low, the beam reaches the ground and paints ground returns.
Try the set-ups. Attenuation: a heavy cell absorbs the beam, and an equally strong cell behind it shows weak or not at all — a radar shadow. Beam width: two cells closer together than the beam is wide show as one echo. High altitude: from FL350 with the antenna level, tilt down step by step and watch a storm appear. Data-link NEXRAD: the image shows where the weather was; a storm moving at 40 kt has moved 10 NM in a 15-minute-old image.
The readout names each cell's intensity as displayed and as it really is in the beam, with the reason when they differ. Practice asks for intensity terms, explains a display and sets the tilt. Whatever the display shows, radar does not show turbulence, clouds, fog or icing: avoid heavy or extreme echoes by at least 20 NM.
Assumption and limits: a schematic training model, not a radar simulator and not for navigation. The storm cells, their reflectivity shape, the weaker frozen tops, the attenuation rate (k = 0.000137 × Z^0.78 dB per km, one way, a 3-cm radar), the range compensation to 60 NM, the ground returns and the colours are model choices; the data-link image is a simple composite of where the cells were. Real radars differ: learn your own from its manufacturer's guide. The FAA texts cited set the principles and the intensity terms.
Radar principles from the FAA-H-8083-28B Aviation Weather Handbook (2026), chapter 15: most aircraft radars have a peak power under 50 kW and a 3-cm wavelength (the WSR-88D: 750 kW, 10 cm) (15.2.3, 15.2.4); precipitation attenuation is significant at 3 cm, so aircraft radar may show only the leading edge of extreme echoes (15.2.5.1); airborne radars compensate for range attenuation only out to 50 to 75 NM (15.2.5.2); targets must be one beam width apart to show separately — the WSR-88D's 0.95° beam is about 1 NM wide at 60 NM and 2 NM at 120 NM, aircraft beams are 3 to 10° (15.2.6.1); with normal refraction the beam's height above the surface increases with range (15.2.7.1), so the lowest beam can overshoot shallow precipitation (15.2.8: about 18,000 ft at 124 NM and 54,000 ft at 248 NM for the WSR-88D); ground clutter (15.2.10); reflectivity depends on particle size, state, concentration and shape (15.2.15.1). Advisory Circular 91-74B 2-4 b: clouds of ice particles have about 20 times less radar reflectivity than rain, and airborne radar receives little return at high altitude unless tilted down near or below the freezing level.
Intensity terms: LIGHT (< 26 dBZ), MODERATE (26 to 40 dBZ), HEAVY (> 40 to 50 dBZ), EXTREME (> 50 dBZ) (AIM, effective 9 July 2026, 7-1-12; Aviation Weather Handbook Table 24-8 prints the extreme row as "50+ dBZ" — 50 dBZ itself is heavy under both texts' "> 40 to 50"); light precipitation from 15 dBZ (24.6.1.4). Limitations: radar does not detect clouds and fog (AIM 7-1-11) or turbulence (AIM 7-1-26; AWH 22.8.1: Doppler turbulence modes detect only turbulence with precipitation, never clear-air turbulence); hail always gives an echo but may fall miles from the nearest visible cloud, and turbulence can extend 20 miles from the echo edge (AWH 22.8.1); ice crystals of high ice water content may not be visible to airborne radar (AC 91-74B 1-4 c, 2-4).
Avoidance and data-link weather: avoid by at least 20 miles any thunderstorm identified as severe or giving an intense, heavy or extreme echo; such echoes should be 40 miles apart before flying between them (AWH 22.8.2 item 14; the AIM 7-1-27 says "intense radar echo"); circumnavigate the whole area if more than half of it is covered (AWH) or with 6/10 coverage (AIM 7-1-27). Data-linked NEXRAD mosaic imagery shows where the weather was, not where it is, and may be 15 to 20 minutes older than the age shown; it is for strategic route selection, never for tactical manoeuvring through a thunderstorm area (AIM 7-1-9 — strategic about 20 minutes or more, tactical under 3 minutes — and 7-1-27; AWH 22.8.2 items 7, 8 and 11). FIS-B transmits the CONUS NEXRAD mosaic every 15 minutes and the regional one every 2.5 minutes (AIM TBL 7-1-9). Advisory Circular 00-24C, Thunderstorms, was cancelled on 22 December 2022: the FAA consolidated its weather ACs into the Aviation Weather Handbook, which this tool cites instead.
- FAA-H-8083-28B Aviation Weather Handbook (2026): 15.2.3-15.2.15 (radar principles: power, wavelength, precipitation and range attenuation, beam resolution and width, normal refraction, overshooting, ground clutter, reflectivity of liquid and frozen precipitation), 22.8.1-22.8.2 (airborne weather avoidance radar; radar shadow; hail and turbulence beyond the echo; thunderstorm avoidance guidance, data-linked NEXRAD), 24.6.1.4 and Table 24-8 (echo intensities and the WSR-88D intensity terminology)
- Aeronautical Information Manual (effective 9 July 2026) 7-1-9 (Flight Information Service: tactical versus strategic use; TBL 7-1-9 NEXRAD update and transmission intervals), 7-1-11 (weather radar services: clouds and fog not detected), 7-1-12 (precipitation intensity: LIGHT < 26, MODERATE 26 to 40, HEAVY > 40 to 50, EXTREME > 50 dBZ), 7-1-26 (thunderstorms: radar does not detect turbulence; 20 miles), 7-1-27 (thunderstorm flying: data-linked NEXRAD 15 to 20 minutes older than shown)
- Advisory Circular 91-74B, Pilot Guide: Flight in Icing Conditions (8 October 2015, active): 1-4 c and 2-4 (high ice water content not visible to airborne radar; ice-particle clouds about 20 times less reflective than rain; tilt down near or below the freezing level)
- Advisory Circular 00-24C, Thunderstorms (19 February 2013): cancelled 22 December 2022 - the FAA consolidated its weather advisory circulars into the Aviation Weather Handbook, which this tool cites instead (FAA advisory circular record, read 17 October 2026)
- Model choices of this tool (stated on the page): schematic storm cells (core reflectivity falling off to the edge, weaker above the freezing level), a 4/3-earth beam, beam sampling across the beam width, X-band attenuation k = 0.000137 x Z^0.78 dB per km one way, range compensation to 60 NM, ground returns, the colour scale, the data-link image as a composite of where the cells were, practice questions