Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
377 FXUS65 KBOI 181707 AFDBOI Area Forecast Discussion National Weather Service Boise ID 1007 AM MST Tue Nov 18 2025 .DISCUSSION...An extensive area of fog/stratus extends across SE Oregon and the lower Snake Plain of SW Idaho this morning. Areas that went down in dense fog are seeing visibility improve and that trend will continue through the rest of this morning. With only patchy coverage, have expired the Dense Fog Advisory at 10MT/9PT. Stratus/fog will burn off through this afternoon as mostly sunny skies prevail above the near surface layer. Expect fog stratus to reform tonight across portions of SE Oregon and through most of the lower Snake Plain (Twin to Ontario). Current forecast is on track for the rest of today. && .AVIATION...LIFR in dissipating fog this morning through early this afternoon. Ceilings will gradually rise and clear through the day to VFR. IFR/LIFR conditions will return to the area tonight and tomorrow morning from fog/low stratus. Surface winds: light and variable. Winds aloft at 10kft MSL: S-SW 5-15kt. KBOI...Fog in the region has begun dissipating, but low clouds may remain for an hour after visibility improves. Then, VFR through this evening before another 50% chance of fog/stratus returns tonight. Surface winds: variable and light. && .PREV DISCUSSION... SHORT TERM...Today through Thursday night...A large upper level low pressure system to the south and a weak upper level trough to the north today will continue relatively quiet weather across the forecast area, with one exception. Dense fog has formed in several valleys this morning as a result of low moisture from yesterday`s rainfall and weak diffuse flow aloft. Area webcams and satellite imagery show the densest fog across the Lower Treasure Valley into the Upper Weiser Basin, and this is expected to last through the morning commute period. Temperatures remain well above freezing, but visibilities are a quarter mile or less, especially from Ontario through Nampa. Long Valley as well as part of Baker Valley are also seeing patchy dense fog. Easterly winds in the Upper Treasure Valley have kept fog west of Boise, though it is possible (50 percent chance) it does move into Boise later this morning. Please allow extra time this morning during the commute. Fog should largely dissipate by this afternoon along with any low clouds. The weak upper level trough passage today will bring a 20 to 40 percent chance of mountain snow above 5000 to 6000 feet, with valley rain in Baker County and the West Central Mountains. Temperatures will cool slightly from yesterday but remain about 10 degrees above normal in the lower valley for this time of year. Fog looks to redevelop again tonight in the valleys. The latest high-res runs this morning have shifted the fog development eastward through much of the Treasure Valley. Another Dense Fog Advisory may be needed tonight. A 20 percent chance of showers across the higher terrain Wednesday afternoon as the another weak trough moves east across the area. A weak shortwave ridge follows as another split trough reaches the Pacific Northwest coast. Much like the current system, the main parts of this system will be south (closed low) or north (open trough), leaving the forecast area between for low chances (15 to 25 percent) for precipitation across the higher terrain. Temperatures will remain 5 to 10 degrees above normal through the period. LONG TERM...Friday through Tuesday...With the upper-level low moving down the California coast, upper-level flow over the area will be largely nebulous. Fog looks to be a regular occurrence with this weak pattern, especially in valley floors. Flow will become zonal Sunday thanks in part to an upper-level ridge well off the coast of California, however it will be short lived from a developing upper-level trough in the Gulf of Alaska. This quickly moves onshore into the Pacific NW late Sunday/early Monday, with long range models disagreeing on timing and intensity. Regardless, widespread PoPs of 20-40% chances exist from early Monday through the extended as this trough makes its way east. Highest chances of PoPs will be in the west-central Mountains, where snow levels will be 3500-4500 feet MSL behind a cold front. && .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...DG AVIATION.....JM SHORT TERM...JDS LONG TERM....CH