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Forecasting Aircraft Icing Jonathan Leffler Chicago CWSU

Forecasting Aircraft Icing Jonathan Leffler Chicago CWSU. Agenda. Definitions (review) Considerations Synoptic Conditions Methodology Mitigation Procedures Icing Products & Reporting Final Thoughts. Definitions. Types

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Forecasting Aircraft Icing Jonathan Leffler Chicago CWSU

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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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