Area Forecast Discussion
Issued by NWS Boise, ID
Issued by NWS Boise, ID
210 FXUS65 KBOI 301556 AFDBOI Area Forecast Discussion National Weather Service Boise ID 956 AM MDT Tue Apr 30 2024 .DISCUSSION... Today, a large upper-level trough lingers over the northern Rockies and Pacific Northwest, maintaining breezy conditions, particularly along the Nevada border. Showers are expected across our northern zones this afternoon and evening. The upper-level jet positioned over our southern forecast area will contribute to breezy winds this afternoon, though not as strong as yesterday. Nonetheless, these winds will usher in much colder temperatures later today. CU clouds are already visible on satellite imagery, forming over the higher terrain of Baker County and the West Central Mountains of Idaho this morning, outside of the stratus deck. As the next shortwave approaches from the northeast and the mid- level stratus deck moves out, conditions will become more favorable for the development of showers and possibly a few thunderstorms. Temperature profiles indicate the potential for mixed precipitation, particularly with the stronger showers, which could include snow, graupel, and rain. However, surface temperatures are expected to remain above freezing, limiting accumulations to the mountains above 4500 feet. A shortwave and weak cold frontal passage early Wednesday will bring increased winds to the area, particularly affecting the Western Snake River Plain. Gusty winds are likely to persist through Wednesday afternoon, possibly reaching advisory levels in the Western Magic Valley and Camas Prairie. This potential will be assessed further in the afternoon package. && .AVIATION...Mainly VFR. Isolated to scattered rain/snow showers north of KBNO-KEUL-KSUN line. Snow showers obscuring mountains and producing brief MVFR conditions. Snow levels 3000-4000 ft MSL. Surface winds: W-NW 5-15 kt, gusts to 20-25 kt between Tue/20z- Wed/03z today. Winds aloft at 10kft MSL: W 20-30 kt. KBOI...VFR with scattered/broken clouds 7000-10000 ft AGL. Isolated showers will pass north of terminal Wed/08z-12z, but there is currently less than 10% chance of showers entering the 10 mile vicinity. Snow level dipping as low as 3000-3500 ft MSL overnight. Light and variable surface winds becoming NW and gusty after Tue/20z with a 30% chance of gusts reaching 25 kt. && .PREV DISCUSSION... SHORT TERM...Today through Thursday night...Unsettled conditions will continue through the short term period as the upper level trough moves east. Temperatures will be below normal today, with lows reaching near freezing in the Treasure Valley tonight. Upper level zonal flow will bring gusty winds as a tight pressure gradient remains over the region today and tomorrow. Gusty westerly winds will increase over the region this afternoon, with sustained winds around 15-25 mph and gusts to 40 mph. Afternoon showers will begin to spread over Baker County, OR and the West Central Mountains by early afternoon today and tomorrow, then into the Lower Treasure Valley by late evening each day. There are much lower chances for precipitation near the ID-NV border (10-20% chance) tomorrow afternoon as well. Snow levels will be around 2500-4000 feet today as the cold air mass centers over northern Idaho, so most of the precipitation will fall as snow in higher terrain. Minimal accumulations are anticipated with this snowfall, with most areas seeing 1-2 inches of snow through Wednesday morning. Weak instability this afternoon will also allow for low chances (<10% chance) of a thunderstorm over high terrain in Baker County/West Central Mountains. Instability will persist Wednesday afternoon as well, with the best chance for thunderstorms over the Central ID mountains, although low confidence exists. A very weak ridge will build into the region late Wednesday night, bringing dry conditions and a brief warm up to near normal daytime temperatures on Wednesday. Then, a shortwave trough will move into the region on Thursday, bringing widespread precipitation, although there is some variation in model guidance on the location and timing of precipitation. Snow levels look to increase slightly on Thursday, to around 4000-5000 feet. LONG TERM...Friday through Tuesday...A quick moving shortwave ridge will bring dry weather to much of the region Friday, the exception being a 15-20% chance of showers across the w-central Idaho mtns. From there agreement in the 00Z deterministic models quickly breaks down with how to handle the progression of an upper low emerging from the Gulf of AK. The GFS shows a more southwest track with the low entering CA while the EC/Canadian bring the low directly through the Pac NW. By Sunday the ensemble clusters back the EC solution with 60% of the members favoring a shortwave trough over the inland NW while the GFS solution is more of an outlier with support from about 20% of the members. Interestingly a blend of these solutions which would bring the low in through Oregon and across northern NV is close to the 00Z ECMWF AI solution. This blend is the current forecast and results in a widespread 30-60% chance of precipitation and liquid totals of over 0.10" from late Saturday through Sunday night. This forecast blend keeps snow levels between 5500-6500 feet late Sat/Sun. Certainly a storm to watch as a shift toward the colder/wetter EC solution could result snow levels down to lower valley floors Sunday morning. All solutions show a broad trough lingering over the NW Monday and Tuesday which will keep a mid-range chance of showers across the region. Temperatures are near normal through Saturday with the forecast spread increasing dramatically on Sunday before returning to a consensus on slightly below normal temperatures Mon/Tue. && .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 DISCUSSION...JDS AVIATION.....SH SHORT TERM...SA LONG TERM....DG