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:

• A pilot's initially chosen IFR alternate, forecast VFR, rapidly deteriorated to IFR conditions due to localized fog while en route, requiring a swift change of plans.
• The incident highlighted the critical importance of continuous TAF trend analysis ("weather forensics") to anticipate worsening conditions and develop a backup plan before an approach.
• VFR alternates, particularly in areas like eastern Washington and Oregon valleys during winter inversions, can quickly transition to IFR, making dynamic weather monitoring essential for flight safety.

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