The Treasure Valley and central Idaho are preparing for another round of wet weather as an upper-level storm system approaches from California, bringing showers and cooler temperatures before conditions improve for the weekend.
What's Driving This Weather Pattern
An upper low-pressure system currently positioned along the central California coast is the culprit behind our midweek weather changes. This system will lift northeast through Wednesday, bringing moisture back to southwest Idaho and far southeast Oregon.
This isn't just a simple passing shower. A shortwave rotating around the low-pressure system is expected to develop a more organized band of precipitation across southwest Idaho late Tuesday night into Wednesday - similar to what we experienced Tuesday morning, but potentially more developed.
Wednesday's Main Event
Wednesday brings the most significant weather of the week, and it's worth paying attention to the timing. The heaviest precipitation is most likely to develop between Twin Falls and Boise, though some high-resolution weather models suggest the rain band could reach as far west as the Boise metro area by Wednesday morning.
Rainfall amounts are expected between one-tenth and one-quarter of an inch across most areas, with the mountains potentially seeing up to half an inch. That's enough to make roads slick during the morning commute.
Snow levels will remain high at 6,500 to 8,000 feet, limiting any accumulating snow to only the higher peaks in central Idaho.
The Cool Down and Frost Potential
As the system moves through, it's bringing a cool air mass that will allow temperatures to dip into the 30s in lower valleys Wednesday night and Thursday morning. This creates potential for frost, particularly in more sheltered areas where winds won't be as strong.
However, steady northwest winds overnight will help mix the air and limit frost development in most areas. Still, gardeners and those with sensitive plants should keep an eye on conditions.
Weekend Recovery
The weather story gets much better for weekend plans. Thursday marks the beginning of improving conditions with sunny skies, though it will remain breezy with afternoon wind gusts potentially reaching around 30 mph southeast of Boise.
Friday and Saturday look ideal for outdoor activities, featuring sunny skies with pleasant temperatures climbing from the low 60s to the mid-60s. Overnight lows will remain comfortable in the low 40s.
Next Week's Uncertainty
Sunday introduces some uncertainty that weather forecasters are watching closely. There's disagreement among weather models about the strength of an approaching storm system, creating a forecast challenge.
About half of the computer models show a deep, wet trough digging into the region Sunday evening, which would drop temperatures 10 degrees below normal for Monday and Tuesday and bring significant precipitation chances. This scenario could also drop snow levels to 4,000-5,000 feet with several inches of snow possible in central Idaho ridges.
The other half of the models keep the system much weaker, limiting both precipitation amounts and temperature drops. Given that the major forecast models are leaning toward the stronger system, I am favoring the cooler and wetter scenario for early next week.
Daily Forecast
Tonight: A 20% chance of showers after midnight. Patchy fog after 3 a.m. Otherwise, partly cloudy, with a low around 42 degrees. Light wind.
Wednesday: Showers likely, mainly before noon with temps in the low 40s. Areas of fog before noon. Otherwise, mostly cloudy with some partial clearing by late afternoon, with a high near 58 degrees. Light wind. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.
Thursday: Sunny, with a high near 61 degrees. Calm wind becoming west northwest 5 to 9 mph in the morning.
Friday: Sunny with a nice afternoon, with a high near 63 degrees.
Friday Night: Mostly clear, with a low around 40 degrees.
Saturday: Sunny with a very pleasant afternoon and a high near 66 degrees.
Saturday Night: Mostly clear, with a low around 48 degrees.
Sunday: A 50% chance of showers. Morning sunshine then increasing clouds and late-day showers. Still mild with a high near 68 degrees.
Sunday Night: A 50% chance of showers. Mostly cloudy, with a low around 41 degrees.
Monday: A 30% chance of showers. Mostly sunny, with a high near 57 degrees.
Tuesday: Mostly sunny, with a high near 56 degrees.
Stay connected right here for updates to my weekend forecast and check out my one-minute ScottScore Forecast on my Facebook.
