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Aircraft Icing Forecasting: Types, Conditions, and Mitigation Strategies for Safe Flight

Explore the definitions, considerations, and methodologies of forecasting aircraft icing, including types like rime and clear ice. Learn about synoptic conditions, mitigation procedures, and available icing products and reporting tools to ensure safe aviation operations.

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Aircraft Icing Forecasting: Types, Conditions, and Mitigation Strategies for Safe Flight

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  1. Forecasting Aircraft Icing Jonathan Leffler Chicago CWSU

  2. Agenda • Definitions (review) • Considerations • Synoptic Conditions • Methodology • Mitigation Procedures • Icing Products & Reporting • Final Thoughts

  3. Definitions • Types • Rime: Whole droplet rapidly freezes, traps air, forms brittle, opaque, milky-colored ice. Most common form. • Clear: Small part of drop freezes, rest smears along surface, less opaque, denser than rime. Greatest threat. • Mixed: Combination of rime + clear. Can appear as layers of opaque and clear. Accumulates like clear, more difficult to remove than rime. Common Temperature Ranges * Icing typically not found < -20 C to -25 C due to the minimal availability of supercooled liquid

  4. Definitions • Rates of Accumulation • Trace: Typically not hazardous to flight. De-icing, anti-icing and altitude change normally not required < 1 hr. • Light: Occasional use of de-icing or anti-icing is required to remove or prevent accumulation. Could become problematic if duration > 1 hr. • Moderate: Short encounter can be hazardous. Use of de-icing or anti-icing equipment is necessary and heading/altitude change normally required. • Severe: De-icing or anti-icing equipment cannot control or remove hazard. Immediate heading/altitude change required.

  5. Considerations • Seasonality: Fall through Spring, Summer TS • Supercooled large drops (solid ↔ liquid, e.g. FZRA) • Liquid water content, not ice content (hard to measure) • Temperature advection (warm/cold), 0 C & -20/-25 C • Droplet Size (rain/drizzle/cloud) • Depth & duration of moisture (horizontally/vertically) • PIREPS! What has already been reported?

  6. Considerations Frequency of icing type occurrence

  7. Synoptic Conditions

  8. Synoptic Conditions Cold Front • Usually not widespread • Faster moving • Clear more than Rime • Heavier ice w/Cu vs St Warm Front • More widespread clouds • Longer residency • Rime more than Clear • Heaviest in FZRA

  9. Synoptic Conditions

  10. Synoptic Conditions Freezing Precip = Highest Threat • Snowflake to raindrop phase transition • Generates supercooled large drops (SLDs) • Greater moisture availability • Clear ice freezing process (dense, hard to remove) • Rapid accumulation →Severe

  11. Synoptic Conditions 40-45 hr/yr 30-35 hr/yr

  12. Methodology • Satellite: Visible & Infrared • Surface moisture contamination (snow cover) • Cloud type (stratus vs cumulus) • Observations • Surface precipitation type (DZ, RA, SN) • Heavy moisture in dendritic “snow” zone tends to scrub supercooled droplets (more freezing process) • Cloud base & height • Radar + Sounding: Bright Band Height • AWIPS 4-Panel Interrogation (NWS) - Initial Areas • BUFKIT Soundings (Work/Home) - Refined Areas

  13. Methodology ~ 050-070 SLD Threat MOD or greater potential 0 C

  14. 020-050 SFC-020 100-140 050-100

  15. SFC-020 ? ?

  16. 020-050 ? Lake Effect ?

  17. 050-100

  18. 100-140

  19. Sampling Locations 075 Snow Zone RUC 18Z - KORD T + 4 (22Z) *Forecast* 015

  20. 075 Snow Zone RUC 18Z - KORD T + 9 (03Z) *Forecast* 015

  21. 055 Snow Zone 035 RUC 22Z - KORD T + 0 *Analysis*

  22. The Forecast ISOL LGT ICGICIP AOB 070.

  23. The Results What does MOD ICG look like? ISOL LGT ICGICIP AOB 070.

  24. 180 LGT Snow Zone 130 MOD RUC 18Z - KORD T + 4 (22Z) FWA 01 Feb/21Z 010

  25. 180 Snow Zone LGT 130 MOD SLD Threat CMI 01 Feb/21Z 005

  26. Mitigation Procedures • Ascend into colder layer (< -20 C), typically safest based on accumulation potential • Descend into warmer layer (> 0 C), but caution... • Lateral into FEW/SCT deck vs BKN/OVC deck Cold soaked skin = delayed warming and susceptible to icing with increased moisture

  27. So where do I go now ?

  28. Icing Products & Reporting http://aviationweather.gov/adds

  29. Icing Products & Reporting

  30. Icing Products & Reporting Graphical AIRMETS http://aviationweather.gov/products/gairmet

  31. Icing Products & Reporting AIRMETS/SIGMETS

  32. Icing Products & Reporting PIREPS Java Tool

  33. Icing Products & Reporting http://aviationweather.gov/adds

  34. Icing Products & Reporting Current Icing Potential (CIP) Forecast Icing Potential (FIP) CIP / FIP = Help pages on how icing analyses and forecasts are done

  35. Icing Products & Reporting Experimental Icing Products

  36. Icing Products & Reporting Experimental Icing Products

  37. Icing Products & Reporting Experimental Icing Products

  38. Final Thoughts • Icing can be a deadly aviation hazard if not planned for in advance. • Icing is subjective, however there are objective ways to forecast potential. We need your PIREPS! • Lots of web-based tools to help you flight plan • Graphics and literature courtesy AFWA TN-98/002 • Special thanks to Robb Kaczmarek (Chicago CWSU) and Paul Merzlock (NWS Romeoville) for technical advice and support

  39. Questions ?

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