To determine the freezing level and areas of probable icing aloft, the pilot should refer to what source?

Inflight Aviation Weather Advisories are specifically designed to provide pilots with critical information regarding current weather phenomena that could affect flight safety, including the freezing level and areas where icing is likely to occur. These advisories are updated frequently and are essential for pilots flying in areas where icing may be a concern, especially when flying at altitudes where freezing temperatures are prevalent.

Pre-flight weather briefings, while informative and useful for initial planning, do not provide the same level of detailed and timely updates as inflight advisories. Terminal Aerodrome Forecasts (TAFs) focus mostly on expected weather conditions at specific airports and might not explicitly indicate freezing levels or icing conditions en route. Area Forecasts can provide a broader outlook on weather patterns but are less focused on immediate hazards like icing and freezing levels encountered during flight.

Thus, the best source for understanding real-time conditions regarding freezing levels and potential icing during flight is indeed the inflight Aviation Weather Advisories.