A dry cold front will bring breezy winds and slightly cooler temperatures to the region today, but the real weather story is the active and potentially stormy pattern developing for the end of the week and into the weekend.
Short-Term Cooldown and Increasing Moisture
A weak and dry cold front will exit the area to the east tonight, leaving behind a brief period of light winds and mostly clear skies. This will allow temperatures to drop into the 30s for many mountain valleys and the low 40s in the Treasure Valley overnight.
On Wednesday, the weather pattern begins to shift as a closed low-pressure system off the northern California coast starts to influence the region. This system will pull warmer air and mid-level moisture into southeast Oregon by Wednesday afternoon. While the lower levels of the atmosphere will remain somewhat dry, there will be enough instability to support a 10 to 20 percent chance of thunderstorms and a 20 to 40 percent chance of showers across Harney and Malheur Counties. Temperatures on Wednesday will be about 5 degrees cooler than today across most areas due to the post-frontal airmass.
Thunderstorm Chances Expand Thursday
The coverage of precipitation will increase on Thursday as the closed low moves closer to the coast, strengthening the southerly flow. This flow will allow temperatures to rebound quickly, with highs returning to the low to mid-70s in the lower valleys.
The combination of increased moisture, daytime heating, and cooling temperatures aloft will create a more favorable environment for thunderstorm development. Expect shower and thunderstorm chances to spread across most of southeast Oregon and into far southern Idaho, particularly near the Nevada border. These thunderstorms will be capable of producing gusty outflow winds and small hail. Showers will likely continue into Thursday night as the main trough axis edges closer to the region.
Active and Stormy Weekend Ahead
The upper-level low off the California coast will move onshore Friday into Saturday. Quickly following this, another upper-level low from the Gulf of Alaska will move into the Pacific Northwest Saturday into Sunday. Both systems will provide sufficient moisture, instability, and lift for widespread showers and thunderstorms.
Increased moisture from this pattern will lead to precipitable water values hovering around the 90th percentile for this time of year on Friday. Friday will support a 30 to 70 percent chance of showers (highest near the Nevada border) with a 15 to 25 percent chance of thunderstorms.
On Saturday and Sunday, the upper-level trough from the Gulf of Alaska will become the predominant system, moving directly overhead. The additional lift provided by this system will act on the abundant moisture in place to further increase shower chances to 60 to 90 percent and thunderstorm chances to 15 to 25 percent.
Precipitation Totals and Cooling Temperatures
Precipitation totals from late this week through the weekend should be light to moderate on average, with 0.3 to 0.5 inches expected in lower elevations and 1 to 1.25 inches in higher elevations. However, heavier amounts will be possible from thunderstorms.
Temperatures will cool to near-normal values Sunday through Tuesday as the trough moves overhead. Snow levels will remain high, above 8,000 feet, through Saturday, then fall to around 5,000 to 7,000 feet on Sunday and 4,500 to 6,000 feet by Monday and Tuesday. Winds will be breezy under this pattern, especially on Monday as the trough exits the area.
Tonight
Partly cloudy, with a low around 40. NW wind 5-15 mph becoming calm after midnight.
Wednesday
Mostly sunny & continued mild, with a high near 71. Wind NW 5-7 mph.
Wednesday Night
Partly cloudy, with a low around 44. North northwest wind around 6 mph becoming calm in the evening.
Thursday
Sunny & very pleasant, with a high near 75. Light wind.
Thursday Night
Partly cloudy, with a low around 47. Light wind.
Friday
A 20 percent chance of showers and thunderstorms after noon. Mostly cloudy, with a high near 74.
Friday Night
A 40 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 50.
Saturday
A chance of showers, then showers likely and possibly a thunderstorm after noon. Mostly cloudy, with a high near 69. Chance of precipitation is 70%.
Saturday Night
Showers likely and possibly a thunderstorm before midnight, then a chance of showers. Mostly cloudy, with a low around 43. Chance of precipitation is 60%.
Sunday
A chance of showers, with thunderstorms also possible after noon. Mostly cloudy & much cooler, with a high near 57. Chance of precipitation is 50%.
Sunday Night
A 20 percent chance of showers. Mostly cloudy, with a low around 39.
Monday
A 20 percent chance of showers. Mostly sunny, with a high near 59.
Monday Night
Partly cloudy, with a low around 38.
Tuesday
Mostly sunny, with a high near 64.
