Western Idaho’s persistent stagnant weather pattern is intensifying, prompting officials to issue a Dense Fog Advisory for the Lower Treasure Valley. The strengthening high pressure ridge is deepening valley inversions and trapping both cold air and pollutants near the surface.
Dense fog advisory in effect
A Dense Fog Advisory has been issued for the Lower Treasure Valley from late tonight through Wednesday morning as high-resolution weather models indicate a higher probability of dense fog redeveloping. The strengthening inversion pattern is creating ideal conditions for thick fog formation that will significantly reduce visibility.
Confidence in dense fog reaching Boise Wednesday morning stands at around 30%, while patchy fog is expected across the Upper Treasure Valley, Western Magic Valley, and sheltered mountain valleys. Areas caught in the fog will experience very little temperature variation throughout the day.
Persistent fog challenges
The fog and low clouds will be particularly difficult to dissipate, especially in the Lower Treasure Valley and Long Valley on Wednesday. The strengthening ridge pattern means fog will likely return across much of the Snake River Plain and sheltered valleys Wednesday night into Thursday.
Weather models have struggled to accurately capture the cold air trapped within these inversions, making precise fog forecasting challenging. However, the overall pattern strongly favors continued fog development in valley locations.
Temperature inversions deepen
As the upper-level ridge strengthens, valley inversions will continue deepening, creating stark temperature contrasts across the region. Valley locations will see highs near or slightly below normal, while mountain areas experience temperatures 5 to 10 degrees above normal…