Mid-January brings persistent temperature inversions to Pacific Northwest valleys, trapping cold air beneath warmer layers and creating dense, stubborn fog that can last for weeks. The Willamette Valley, Puget Sound lowlands, and other inland basins experience these conditions most severely, with fog sometimes persisting continuously for 10-14 days. During inversions, valley temperatures may remain in the 30s-40s while nearby mountain locations bask in sunshine and temperatures 20-30 degrees warmer. This phenomenon creates eerie landscapes where the sun becomes a pale disk behind thick gray mist, and frost persists on vegetation throughout the day, coating everything in crystalline white.

Mid-January features continued abundance of storage crops—root vegetables (beets, carrots, parsnips, turnips), hardy greens (kale, chard), and alliums (garlic, leeks, onions). Winter citrus arrives from California including clementines, tangerines, and grapefruit, brightening gray days with color and vitamin C.

Escape valley fog by heading to mountain elevations—inversions create magical skiing and hiking conditions with brilliant sunshine above the clouds while valleys remain socked in. Set out early for cloud inversion hikes, climbing through fog to emerge in sunshine 20-30 degrees warmer, or ski above the clouds at Pacific Northwest resorts.