Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
812 FXUS65 KBOI 150925 AFDBOI Area Forecast Discussion National Weather Service Boise ID 325 AM MDT Sun Sep 15 2024 .SHORT TERM...Today through Tuesday night... KEY POINTS *Isolated showers and thunderstorms will begin this afternoon in southeast Oregon, with heavy rain and strong winds (35-45 mph gusts) the main concern. *Heavy rain in showers and thunderstorms could bring localized flooding on Monday afternoon-evening, particularly in steep drainages. *Temperatures will begin to cool, with highs about 10-15 degrees below normal by Tuesday. A plume of moisture currently extends from far southeast Montana deep into the Pacific Ocean, bringing low clouds and virga showers across southwest Idaho tonight. This moisture will continue to expand across the area as a deep low pressure system off the Washington State coast moves inland and dives south later today. Winds will increase, especially on higher ridgetops, as the low pressure system moves inland this afternoon. This low pressure system will begin a stark cooling trend through the next week, along with significant rainfall and breezy winds. Showers will increase across Western Harney and Baker County early this afternoon, with southerly flow steadily increasing precipitation amounts especially over the Harney/Malheur County border through this evening. Moderate instability will be present later this afternoon, with CAPE values anywhere from 300-500 J/KG by early evening. This allows for a slight chance of thunderstorms, mainly over southeast Oregon. Showers and thunderstorms will then expand over the Idaho-Nevada border by Sunday night-Monday morning, as the low center moves through Central California. Wraparound precipitation will then bring the bulk of the rainfall to the Central ID Mountains by Monday afternoon, with some pervasive model disagreement on track and amounts of rainfall. Some hi-res models (FV3/HRDPS) show localized precipitation amounts exceeding 0.80-1.00 inches by Monday afternoon. These amounts would bring flash flood/debris flow concerns to the region, especially in burn scar areas. This still appears to be a remote possibility, with most other guidance showing the highest precipitation totals under cores anywhere from 0.3-0.5". This trend in lowering QPF totals is still reflected in the past model runs. .LONG TERM...Wednesday through Sunday...The bulk of the moisture associated with an upper low remains generally to our south as it moves eastward across Nevada and Utah Wednesday and Thursday. However, there is a chance of showers, mainly in southern areas closest to the low. Highest pops (around 60 percent) will be near the Nevada border and generally 15-40 percent chance elsewhere on Wednesday, lowering to less than 15 percent in SE Oregon and 15-40 percent chance in SW Idaho on Thursday. Instability is marginal with this system, but enough to justify a slight chance (less than 20 percent) of thunderstorms. Most models favor drier conditions as a weak upper ridge develops across the area on Friday, but some of the ensemble members depict a slower retreat of the upper low for a slight chance (less than 20 percent) of showers in SW Idaho. Temperatures, while remaining below normal, trend slightly warmer each day. Forecast confidence is low next weekend since the models have varying depictions of another low arriving from the north. Latest forecast will remain dry, except for a slight chance (less than 25 percent) of precip in Baker County and central Idaho Saturday and Sunday. Temperatures remain 5 to 10 degrees below normal. && .AVIATION...VFR. Increasing mid-high level clouds. Scattered showers in SE Oregon along with a slight chance of afternoon thunderstorms. Showers and thunderstorms spreading into SW Idaho after Mon/00Z. Surface winds: variable less than 10 kt becoming mainly NW 5-15 kt after Sun/18Z. Winds at 10kft: SW 10-20 kt. KBOI...VFR. A 30 percent chance of showers after Mon/00Z. Surface winds: variable less than 6 kt becoming NW 5-10 kt after Sun/20Z, increasing to 10-15 kt with gusts to 25 kt after Mon/00Z. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise SHORT TERM...SA LONG TERM....BW AVIATION.....BW