When an aircraft is flying near the top of the cold air mass beneath a deep layer of warm air, serious icing can occur.

• Conditions that make icing worse:
  • Any freezing precipitation
    • Freezing rain / drizzle / sleet
  • Very wet conditions
    • High cloud tops – buckets of water
    • Maritime air
    • Great Lakes / northwest
    • Top 20% of the cloud height
  • Unstable air
    • Over mountains: mechanical lifting / wave action
    • Frontal action: building cumulus
• Conditions that relieve icing situations:
  • Very cold: moisture is mostly frozen ice crystals
  • Sunshine: Sublimation occurs even below freezing
  • Fairly dry: Ice usually not too bad in stratiform
  • Rain [above freezing]: Peels off ice quickly
  • Air [above freezing]: Melts ice off slowly
  • High RPM: Ice accumulates more slowly on prop
• Necessary ice strategies
  • Get a good weather briefing
    • Can detect possibility of freezing rain
    • Get the big picture and WX at every point
    • Can craft 100% our plan [or not]
    • FSS is usually fairly conservative
  • Pilot reports for “NO GOs”
    • Bad reports from larger aircraft
    • Unattainable tops
  • Pilot reports for “GOs”
    • Reports of no ice; can be timely
    • Reliable local tops info
    • Correlate with other WX data
  • Have plenty of fuel
    • Increases options
    • Decreases ROC