textproduct: Boise

DISCUSSION

Cold front along the coast is forecast to dissipate as it moves inland today and will have no impact on our CWA. However, Pacific moisture south of 30N will surge northeastward along the remains of the front and provide significant rain and mountain snow when it reaches our CWA late Monday night through Tuesday. The wide moist band will finally shift eastward and out of our CWA Tuesday night as it centers along a new cold front. This means dry, breezy, and mild weather today through Monday, then increasing clouds and continued mild Monday evening, followed by moderate to heavy pcpn (rain below 6000 feet) late Monday night through Tuesday. Current forecast matches up well with latest guidance. No updates.

AVIATION

VFR. A 15% chance of showers in the mtns around KBKE, which could obscure higher terrain. Surface winds: E-S 5-15 kt, except 10-20 kt with gusts 20-35 kt in the Snake Plain and SE Oregon. LLWS through late morning, then returning again tonight, across SE Oregon. Winds aloft at 10kft MSL: SW 30-50 kt over SE Oregon, and 15-30 kt over SW Idaho.

KBOI...VFR. Gusty SE surface winds through the day.

PREV DISCUSSION

SHORT TERM...Today through Tuesday night...A deep trough off the coast will keep our area in mild and mostly dry southwesterly flow aloft through early Monday. High temperatures today and Monday will average 5-10 degrees above normal. Today will be mostly sunny, but clouds will increase tonight into Monday as the trough approaches. South to southeast winds will be breezy, especially today across the Treasure Valley and higher terrain where gusts 20-35 mph will be common. By Monday afternoon, precipitation chances will start to increase across the northern mountains.

The pattern will shift significantly Monday night and Tuesday as the flow aloft becomes westerly and advects a subtropical plume of moisture into our area. Precipitation chances will increase to 70-100% by Tuesday. The heaviest precipitation will fall across the central Idaho mountains, aided by upslope flow where QPF is 0.75-1.50" (locally higher on the peaks). Snow levels will be high through most of the event, ranging from 5-6kft MSL across the north and 7-8kft across the south. This will bring mostly rain to mountain valleys, with heavy snow limited to elevations above 6-7kft MSL. However, precipitation could begin as snow in higher valleys such as McCall Monday night into Tuesday morning with light snow accumulations possible before mixing with or changing to rain. Even the lower valleys should see significant rain amounts of 0.25-0.50", aided by a warm front and westerly flow aloft producing less shadowing than a southwesterly flow. Widespread precipitation will cool high temperatures by about 5 degrees on average. Winds will remain breezy, strongest in the higher terrain with gusts 25-40 mph.

LONG TERM...Wednesday through Sunday...Precipitation will taper off through the day Wednesday as the early week storm system advances eastward. Mountain valleys could end with some light snow accumulation as snow levels settle to between 4-6kft during the day. The remainder of the week will see northwest flow set up over the region, with the core of the upper jet/storm track cutting through WA and n-central ID. This will keep most of the area dry while the e-central Oregon and w-central ID mtns hold onto a slight chance of light snow. Did trend PoPs lower, closer to the deterministic GFS/ECMWF and NBM5, for the Thur-Sat period. The region is likely to remain locked into northwest flow through the weekend, with uncertainty hinging on the evolution of a closed low off the CA coast. For now a 15-30% chance of precipitation covers much of the area by Sunday, accounting for the potential of the low moving onshore, as depicted by the 00Z GFS. Temperatures are at or slightly above normal through the period, with lower elevations into the mid-50s.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None. OR...None.