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Diagnosis of weather phenomena


- 6.1. Warm frontal rain

The aim of this chapter is for the forecaster to be able to analyze and short term forecast of significant precipitation (intensity and type snow/rain/fzra, icing, shear, embedded convection, location of the front).

  • Structure: overhanging precipitation in front of the front (illustrated with a cross section)
  • Radar products max, tops, CAPPI look different
  • Precipitation type changes often from snow to rain during the event
  • Rapid change in temperature: icing for aviation (link to bright band)
  • Embedded convection
  • Shear
  • Visibility vs. intensity (remember mist)
  • Link to hydrometeor classification by dual polarisation


- 6.2. Cold front (Kata front, film loop, link Doppler)

The aim of this chapter is for the forecaster to be able to analyze and short term forecast of significant precipitation (intensity and type snow/rain/ hail/graupel), shear, embedded severe convection with squall lines, location of the front, diurnal variation

  • Diurnal variation: fronts intensifying for afternoon
  • Effects of the underlying surface: sea/land, orography


6.3. Deep convection cells (also “embedded”, seeding, link to nowcasting)


The aim of this chapter is for the forecaster to be able to analyze and short term forecast of significant precipitation hail/) graupel, shear, squall lines, location of the front, diurnal variation, life cycle

  • Rain bands, bows echoes, hook echo (examples, film loops)
  • MCS, derecho
  • Typical patterns
  • Convergence, downbursts, rotation, etc. What can you get from velocity data?
  • Height of maximum echo
    • stationary showers
  • Elevated echo through nomogram threshold height (hail)
  • Low-level convergence through depth under elevated echo (sustained updraft)
  • Rapidly descending elevated core (damaging wind)
  • Deep, persistent low-level convergence associated with mid-level rotation (Supercell with potential for tornado - damaging wind)
  • Persistent WER / BWER (organised convection / supercell)
  • Hook echo (supercell)
  • Hail flare identified in 10cm radar data
  • Low-level reflectivity gradient on storm-relative inflow flank (organised convection / supercell)
  • Anomalous storm motion identified (organised convection)
  • Slow storm motion (possible flash flooding)
  • Passage of a number of cells over a location (possible flash flooding)
  • Bow-wave echo or Line Echo Wave Pattern (damaging wind)
  • Damaging/destructive winds associated with FFD, RFD in velocity data
  • Storm top divergence in velocity data (powerful updraft indicator - hail)
  • Persistent mid-level rotation in velocity data associated with updraft (supercell)
  • Low-level rotation in velocity data (potential tornado /damaging winds)
  • Mid-level convergence in velocity data (downburst / damaging winds)
  • Low-level divergence in velocity data (downburst / damaging winds
  • Pertinent low-level boundaries identified:
    • Assess speed of movement, depth, anticipate effect on convection


- 6.4 Drizzle and other shallow precipitation events (link problems)


The aim of this chapter is for the forecaster to be able to analyze and short term forecast these events if possible. Estimate at what range you can determine them.

  • Geometry (beam overshooting)
  • Sensitivity (link to radar equation: particle size matters!)
  • Data threshold (application specific, seasonal, location specific: how weak echoes are shown in this product?)


- 6.5 Precipitation and orography

  • Orographic enhancement below radar beam
  • Föhn - evaporation below radar beam
  • Rain here might be snow there


- 6.6. In different weather situations you have different problems

  • cold sea, warm continent > anaprop
  • strong convection > 2nd trip echoes, hail flare, attenuation
  • bird migration


- 6.7 Some principles of diagnosis

  • “What is that” how do you explain
  • do we have dBZ gradients
  • height of maximum echo
  • do not look at a echo alone, is there something else between it and the radar (attenuation risk)
  • look at other radars
  • look at other sources of information than radar alone

Material to this section is available through:

- Laurent Delobbe: animations, PowerPoint presentations and case study material
- Roger Deslandes: animations, PowerPoint presentations, quizzes and case study material
- Wilfried Jacobs: animations, PowerPoint presentations, case study material and other
- Evelyn Murphy: PowerPoint presentations
- Paul Joe: animations, PowerPoint presentations and case study material
- Günther Haase: PowerPoint presentations

mise jour Wednesday 4 May 2016