The warm and dry pattern continues across southwest Idaho as a broad ridge of high pressure remains locked over the western United States. This ridge has kept storm systems deflected to our north, allowing an atmospheric river to feed moisture into Washington and northern Idaho while our region stays mostly dry. With light winds and a surface inversion in place, valleys are experiencing periods of stagnant air that are expected to linger through at least Sunday night.
Temperatures remain unusually mild—running about 15 to 20 degrees above average—but daytime highs won’t be quite as warm as they were midweek.
Looking ahead to early next week, above-normal temperatures continue as high pressure holds strong over the Intermountain West. The ridge shifts east on Sunday, allowing clouds to increase as a weak low pressure system passes by to our south. This system may bring a subtle uptick in westerly winds, though likely not enough to mix out any remaining low clouds or improve air quality in the valleys.
The next opportunity for a pattern shift comes Tuesday as another atmospheric river sets its sights on the Pacific Northwest. Some of that moisture may spill into southeast Oregon and central Idaho, but mainly for the higher elevations. Snow levels will remain unusually high at first—around 7,000 to 8,500 feet—before gradually lowering into the 5,000 to 6,000 foot range by Wednesday as slightly cooler air moves in.
Confidence in the forecast drops a bit by midweek because long-range models disagree on how strong the Pacific ridge will remain. A stronger ridge would block most of the moisture and keep showers focused north and west of our region. A weaker ridge would allow more of that atmospheric river to slide farther inland. At this point, the most likely scenario keeps precipitation limited, with only light amounts possible in mountain valleys and lower mountain zones. Temperatures look to stay well above normal—running about 10 to 20 degrees higher than typical for mid-December.
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