Colors on a weather radar echo map indicate precipitation reflectivity received by radar antennas (measured in decibels of reflectivity, dBZ). As colors transition toward yellow, red, and purple, rainfall intensity escalates. According to Central Weather Administration (CWA) (中央氣象署) educational guidelines, 15 to 20 dBZ signals potential rain, 20 to 30 dBZ indicates light rain, 30 to 40 dBZ indicates moderate rainfall, and values exceeding 45 dBZ signify heavy downpours. Evaluating whether rain will cease requires viewing animated loops on official portals to trace where storm cells originate and travel.
This guide synthesizes official documentation from the Central Weather Administration (CWA) (氣象署) radar portal, digital science resources, and Southern Weather Center into a definitive reference matrix, explaining refresh frequencies, observation limitations, and analytical best practices. Prior to leaving home, check our hyperlocal rain radar tool or our will it rain lookup.
What Is Radar Reflectivity?
The CWA radar portal defines radar reflectivity as electromagnetic pulses returned from atmospheric hydrometeors (rain, snow, hail). Reflected signal strengths are mapped into color-coded radar reflectivity imagery.
Reflectivity scales with the size, geometry, physical state, and volumetric concentration of hydrometeors; stronger return echoes denote higher precipitation intensity. Reflectivity maps quantify atmospheric water content aloft rather than rain collected by ground rain gauges. Severe thunderstorm alerts interpret signals similarly: return strength reflects atmospheric moisture content across liquid, solid, and mixed phases.
Reflectivity differs fundamentally from probability of precipitation. Probability represents a statistical forecast, whereas radar represents physical observation; read 30 percent rain probability explained.
Reflectivity dBZ and Precipitation Intensity Reference Matrix
Official CWA color bars span 0 to 65 dBZ. Descriptions below synthesize CWA educational portals and Southern Weather Center publications. Color assignments reflect CWA standard palettes; consult active map legends for exact calibrations.
| Echo Intensity | Official Classification Description | CWA Palette Representation | Source Authority |
|---|
| Zero Echo | Clear skies, no precipitation echoes; safe for outdoor activities | Colorless transparent | Southern Weather Center |
| Below 15 dBZ | Humid atmospheric layers; light moisture signatures | Pale blue to blue | Southern Weather Center, CWA Legend |
| 15 to 20 dBZ | Precipitation potential exists | Green | CWA Digital Science Portal |
| 20 to 30 dBZ | Light rainfall; prepare umbrella gear | Green to yellow-green (transitions ~26 dBZ) | CWA Digital Science, Southern Center |
| 30 to 40 dBZ | Moderate rainfall; schedule indoor activities | Yellow to orange | CWA Digital Science, Southern Center |
| Above 45 dBZ | Heavy downpour; severe convective gales; shelter indoors | Red, dark red to purple (red starts ~43 dBZ) | CWA Digital Science, Southern Center |
Official sources treat 40 to 45 dBZ as an intermediate transition. Red hues appear on CWA palettes around 43 dBZ, meaning pale red may read below 45 dBZ. National Science and Technology Center for Disaster Reduction (NCDR) radar alerts establish red warnings at 45 dBZ and yellow at 35 dBZ (alert criteria distinct from palette shades).
Different media apps apply customized color palettes; always inspect active map legends first.
Refresh Frequencies and Coverage Boundaries
CWA mosaic radar updates every 10 minutes at 1-kilometer spatial resolution; dedicated dual-polarization X-band rain radars (5 cm wavelength) refresh every 2 minutes at 250-meter resolution across stations in Shulin in New Taipei (新北), Nantun in Taichung, and Linyuan in Kaohsiung. Synthesized radar mosaics populate portals within 15 minutes of antenna sweep completion.
Effective meteorological radar range extends roughly 460 kilometers. Specialized rain radars offer optimal range of 150 kilometers and ideal resolution within 75 kilometers, though heavy precipitation causes signal attenuation. Mountain topography blocks radar beams, designated in blue-gray shading. Near-field ground clutter around Linyuan radar is filtered out, requiring cross-referencing nationwide composite maps.
Furthermore, standard atmospheric refraction modeling introduces minor geometric displacement between radar echoes aloft and ground precipitation, particularly across mountain terrain.
How to Determine When Rain Will Stop
Hydrometeors drift with steering winds. Loop 1 to 3 hours of animated imagery on official portals (available across 3, 6, 9, or 12 hours) to project storm motion:
- Track Motion Direction: Observe overall storm vector trajectory. When upstream sectors show clear skies or blue echoes, rain will abate once active bands pass.
- Monitor Echo Intensity Trends: Convective cells transitioning from red to yellow and green indicate weakening, whereas green echoes expanding to orange and red indicate rapid convective development.
- Evaluate Spatial Footprint: Broad frontal rain bands behave differently from localized convective cells that develop, rain out, and dissipate in situ.
- Exercise Caution with Summer Convective Storms: Summer afternoon thunderstorms develop within 1 to 3 hours with volatile localized steering. Convective cells exploding over mountain ridges can propagate rapidly toward urban plains.
When red or purple echoes approach, or phones receive severe thunderstorm nowcast alerts, secure balcony fixtures and close windows. Check flooding alerts when rains breach heavy rain advisory levels; audit plumbing and electrical work resilience using our pre-typhoon checklist.
Official Portals for Viewing Weather Radar
- CWA Official Radar Portal: Features terrain overlay, non-terrain, and quantitative precipitation radar views.
- QPESUMS Severe Weather Surveillance Portal and Mobile App.
- SOSfix hyperlocal rain radar and Taiwan Today dashboard consolidating warnings and weather telemetry.
Frequently Asked Questions
Why Is No Rain Falling When Radar Shows Green Overhead?
Radar detects hydrometeors aloft. Raindrops can evaporate through dry sub-cloud air or drift downwind before reaching ground level. Green echoes encompass potential rain and light sprinkles; lack of surface precipitation is physically consistent.
Which Is More Accurate: Radar Imagery or Precipitation Probability?
Both serve different forecasting horizons. Radar maps active atmospheric conditions over 1 to 2 hours; probability models predict rainfall over half-day or full-day spans. Consult both before traveling.
Do Red Radar Echoes Guarantee Flooding?
No. Red indicates intense rainfall rates; inundation depends on storm duration, topography, and drainage capacity. Review active alerts on our real-time flood warning dashboard.
Last updated: 2026-10-30
Compiled by SOSfix from official agency records for reference.
Information Sources
- Central Weather Administration: Radar Reflectivity Mosaic (Verified 2026-10-30): Definitions, reflectivity mechanics, 15-minute uploads, 3-12 hour loops, 0-65 dBZ palette scale.
- Central Weather Administration: Rain Radar Portal (Verified 2026-10-30): 5cm wavelength, 2-minute updates, 250m resolution, 150km optimal range, terrain masking, and radar stations.
- CWA Digital Science: Weather Warfare, Reading Radar Hydrometeors: 4 reflectivity ranges (15-20 dBZ potential rain, 20-30 light, 30-40 moderate, >45 heavy downpour).
- CWA Southern Weather Center: Understanding Rain Intensity (Modified 2023-10-24): Color classifications, loop animations, and QPESUMS portal.
- CWA Meteorological Handbook (March 2020 Edition): Chapter 2 Section 10, radar principles and 460km effective range.
- CWA Product Specification: QPESUMS Radar Mosaic (Modified 2024-12-10): Technical constraints on beam elevation and atmospheric modeling.
- CWA Severe Thunderstorm Alert Portal (Verified 2026-10-30): Hydrometeor content interpretations and 1-3 hour convective lifespans.
- NCDR Strong Radar Echo Alert Thresholds (Verified 2026-10-30): Alert benchmarks (>45 dBZ red, >35 dBZ yellow).
