117 FXUS65 KBOI 290231 AFDBOI Area Forecast Discussion National Weather Service Boise ID 831 PM MDT Sat Sep 28 2019 .DISCUSSION...Showers continue over much of the area this evening, with the majority of the activity over the higher elevations. These are associated with a large upper level low centered over north-central Oregon as of 8 pm MDT (7 pm PDT). Thunderstorms remain well east of the area. A band of light warm- air-advection showers will continue over eastern Owyhee County and the western Magic Valley this evening. Latest mesoscale guidance is consistent with previous thinking outlined below. No changes are planned at this time. && .AVIATION...Scattered Rain and snow showers through Sunday. Widespread broken mid and low level clouds and mountain obscuration with periods of MVFR/IFR conditions. In the Snake River Valley mainly VFR except local MVFR ceilings in showers. Snow levels 4k-5k ft MSL tonight lowering to 3500-4500 ft MSL Sunday. Surface winds west-northwest 5-15 kts. Winds aloft at 10k ft MSL west 10-20 kts. && .PREV DISCUSSION... SHORT TERM...Tonight through Monday...A broad area of low pressure will dominate the weather through Monday. The low will slowly drift to the east and southeast over time, with moisture wrapping around the low center and producing areas of showers. There is general agreement among the high resolution models that the heaviest precipitation will be limited to the higher terrain. The best chance for lower valley precipitation will be this afternoon and evening, and again Sunday afternoon. Snow levels are expected to drop below 5000 feet overnight allowing for accumulating snowfall over nearly all mountain areas, including McCall. Portions of the Magic Valley could see the first flakes of the season as well by early Sunday morning. The low will be tracking eastward into northern Utah and eastern Idaho by early Monday, allowing for reduced shower activity and thinning clouds over the most valley locations. The thinning clouds will combine with the cold temperatures of the trough to produce the coldest morning temperatures of the season for lower valleys. Many locations will approach the freezing mark, and if the forecast pans out, a frost will be likely. Those with agriculture interests should monitor the situation closely, and take precautions. LONG TERM...Monday night through Thursday...The upper level trough begins to lift out of the region Monday night ending the precipitation across the region. A brief warming trend begins as the shortwave ridge moves over the Intermountain West Tuesday through Wednesday. Another upper level trough moves over the Pacific Northwest on Thursday with a cold frontal passage. This trough is not nearly as strong as the one over the area this weekend, but strong enough to bring and end to the warming trend and strong enough to bring showers to the region...especially in the higher terrain. Thursday night through Saturday night...Showery and cooler conditions are expected across the northern half of the region as the effects of a strong, low pressure system along the Canadian border moves across that portion of the forecast area. Fairer but cooler weather conditions are expected to prevail elsewhere. Breezy winds should spread across the area, with the help of a tightening pressure gradient. Look for improving conditions by Saturday as the low exits and a drier and more stable airmass rolls in. High temperatures are expected to measure in around 10 degrees below normal while dip down close to 5 degrees below normal. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...SP AVIATION.....JT PREV SHORT TERM...MC PREV LONG TERM....JS/WH