Valley of the Fogs

On a recent trip to Richland, Wash. (KRLD), my destination was forecast to have ceilings at 900 feet at the time of my arrival. That is doable IFR for me if there is no ice. During my TAF trend analysis, I saw that both Moses Lake, Wash. (KMWH), and Pendleton, Ore. (KPDT), had TAFs predicting VFR conditions, making them legal IFR alternates. I chose Pendleton because it was more convenient.

Key Takeaways:

• Even IFR alternates initially forecast as VFR can rapidly deteriorate to unusable IFR conditions en route due to localized weather.
• Continuously monitoring TAF trends and applying "weather forensics" is crucial for anticipating such changes and allowing for a backup plan before commencing an approach.
• Pilots should be particularly aware of rapid VFR-to-IFR transitions caused by fog in valleys during cold, inverted winter conditions.

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