Scattered snow showers are decreasing in coverage as the core of the upper trough moves east, setting the stage for a significant warming trend this weekend before another active weather system arrives early next week.
Tonight Through Friday: Lingering Mountain Snow and Fog Development
Lingering moisture and cold air aloft will maintain a slight chance of light snow in the mountains through overnight hours, though scattered snow showers will continue decreasing in coverage. Snow in the valleys will have time to mostly melt before sunset, leading to increased boundary layer moisture for patchy fog development overnight. The Treasure Valley will have the best chance for fog tonight as temperatures drop dramatically, with mountain areas reaching between -10 to 15 degrees and valleys seeing mostly 20s across the region.
The region remains under the influence of a broad, cool trough through Friday. Another weak shortwave will clip the area Thursday, primarily impacting southeast Oregon and the central Idaho mountains. This will trigger another round of convective snow showers during the afternoon with minimal accumulations of 1 to 2 inches in higher terrain. Lower valleys may see a few light flakes or a brief rain and snow mix, but little to no accumulation is expected as temperatures rise into the low 40s.
By Friday, the trough begins shifting further east and atmospheric heights start to rise. While a few stray showers remain possible over the higher peaks of the west-central and Boise mountains, most areas will see a drying trend. Temperatures will remain 5 to 10 degrees below normal through Friday night, with clearing skies allowing for chilly overnight lows.
Weekend Warming: High Pressure Builds
High pressure builds over the area this weekend as a deep low develops off the Pacific Northwest coast. The high pressure will keep conditions dry with a significant warming trend developing. The offshore low will strengthen the pressure gradient in the southwest flow as it approaches Monday, making Monday the warmest day in the forecast just before the low switches the weather pattern.
Temperatures will rise from near normal Saturday to 5 degrees above normal Monday, with Saturday reaching the upper 40s and Monday climbing to near 58 degrees. This represents a dramatic temperature swing from the recent below-normal readings.
Next Week: Active Pattern Returns
A 10 to 20% chance of precipitation Sunday evening in the far western fringe of the area turns into a 50 to 80% chance Monday evening, with lower percentages in valleys and higher in mountains. This happens as the low rejoins the primary jet stream and carries moisture and favorable dynamics for precipitation through the area.
As the system rejoins the jet stream, the flow becomes zonal and atmospheric heights drop, leading to a slight reduction in temperatures down to normal levels. Snow levels will be near 4,000 to 5,000 feet by Tuesday, dropping further to 3,000 to 4,000 feet by Wednesday.
The precipitation continues from Monday evening through Wednesday morning, before another low off the Pacific Northwest coast stalls and a weak ridge rebuilds over the region. The flow pattern looks to remain moist, but temperatures will stay seasonal rather than continuing the warming trend.
Wednesday Night
Partly cloudy with areas of fog developing. Colder with icy surfaces developing, with a low around 24. Diminishing NW wind
Thursday
Patchy fog before 8am. Otherwise, mostly sunny, with a high near 43. ESE wind 5 to 7 mph.
Thursday Night
Mostly cloudy, with a low around 24. East wind around 5 mph becoming calm in the evening.
Friday
A 20 percent chance of snow showers before 11am. Partly sunny, with a high near 43. Light wind.
Friday Night
Mostly clear, with a low around 24.
Saturday
Mostly sunny, with a high near 48.
Saturday Night
Mostly cloudy, with a low around 32.
Sunday
Partly sunny & milder, with a high near 55.
Sunday Night
A 20 percent chance of rain after 11pm. Partly cloudy, with a low around 38.
Monday
A 40 percent chance of rain. Partly sunny & unseasonably mild, with a high near 58.
Monday Night
Rain likely. Mostly cloudy, with a low around 38. Chance of precipitation is 60%.
Tuesday
A chance of rain and snow. Mostly cloudy, with a high near 54. Chance of precipitation is 50%.
