Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
451 FXUS65 KBOI 181526 AFDBOI Area Forecast Discussion National Weather Service Boise ID Issued by National Weather Service Pocatello ID 926 AM MDT Mon Aug 18 2025 .DISCUSSION... Hot and dry conditions will prevail today under mostly clear skies as the Four Corners ridge begins to build northward. A few thunderstorms are possible this afternoon over northern Valley County (around a 15% chance), but the rest of the area will remain dry. The ridge will strengthen further on Tuesday, reaching peak amplification. Highs today will climb into the mid-90s, then approach 100 degrees in the southern valleys on Tuesday. Yesterdays storms produced widespread lightning across southeast Oregon, with more than 1,000 cloud- to-ground strikes reported. While many locations received wetting rains, new fire starts are likely, which could lead to an increase in smoke and haze over the next couple of days. No forecast updates are planned at this time. && .AVIATION...VFR. Mostly clear skies. Local visibility reductions continue in the W-Central ID Mountains due to wildfire smoke. Surface winds: variable 10 kts or less. Winds aloft at 10kft MSL: SW 10-20 kt. KBOI...VFR. Surface winds: Southeast around 8 kt this morning switching to the northwest this afternoon. && .PREV DISCUSSION... SHORT TERM...Today through Wednesday night...The Flash Flood Watch in eastern OR was extended until 2 AM PDT as thunderstorms with moderate to heavy rain continued in northern Malheur County through Hells Canyon. Radar estimated less than flash-flood rain amounts but still significant. Radar trends and hi res- models say the rains will decrease overnight, shift across Valley County/ID around sunrise, then out of our CWA. Yesterday`s late afternoon and evening thunderstorms produced a huge amount of cloud-to-ground lightning in Harney and Malheur Counties, but also wetting rains. We don`t yet know how many new fires were started, but any fires will likely grow rapidly as hotter, drier, and windier weather is expected in those same areas this afternoon and especially Tuesday afternoon. This will be due to the westward expansion of an upper high centered in the Four Corners area. High temps will be in the mid 90s today and approach 100 degrees in the southern valleys Tuesday. Also, mid-level monsoon moisture will begin to surge northward into southern Idaho beginning Tuesday, but not enough for thunderstorms through Wednesday night. LONG TERM...Thursday through Monday...By Thursday enough monsoon moisture will reach our CWA for a 15 percent chance of thunderstorms near the NV/ID border. Any storms should have strong outflow winds but little rain due to low-level dryness. High temperatures should lower 2-4 degrees by Friday but still reach the mid 90s in the southern valleys, as a weak upper trough moves eastward along the Canadian border. Next weekend looks hotter again, along with another northward surge of monsoon moisture, this time into southern OR and then eastward across southern ID, with gradually increasing chances of thunderstorms, and heightened fire danger due to lightning. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.x.com/NWSBoise DISCUSSION...JDS AVIATION.....JDS SHORT TERM...LC LONG TERM....LC