textproduct: Boise

LONG TERM...Sunday through Thursday

The upper ridge will flatten Sunday as a north Pacific cold front and supporting upper trough move onto the northwest coast. The front will reach our CWA late Sunday night and Monday morning with rain and snow showers, gusty northwest winds, and much cooler air especially aloft. The cooling will weaken the inversion in the underlying valleys. Winds along and behind the cold front should easily be able to clear the stagnant air from the valleys. Tuesday through Thursday will finally cool to seasonable temperatures. There will still be enough moisture for a 30 to 50 percent chance of snow showers in the mountains, but overall those days look drier than Monday.

AVIATION

Generally VFR. Patchy MVFR-IFR visibility from haze/mist in lower basins and sheltered valleys early 05/16Z. Surface winds: variable less than 10 kt, except E-NE 10-15 kt in s-central Idaho. After 05/16Z NE-SE wind expected in all areas. Winds aloft at 10kft MSL: variable 5-15 kt.

KBOI...VFR. Surface winds: SE 3-9 kt until 05/18Z then light and variable.

Weekend Outlook...Continued VFR, except local IFR in the valleys in the mornings due to fog/stratus.

AIR STAGNATION

Little air movement in the valleys through Sunday due to an inversion that will continue under strong high pressure aloft. A Pacific cold front and supporting upper trough will arrive late Sunday night through Monday morning to finally break the inversion, scour the stagnant air, and greatly increase vertical mixing.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Air Stagnation Advisory until 5 AM MST Monday IDZ012-014-016-033. OR...Air Stagnation Advisory until 5 AM MST /4 AM PST/ Monday ORZ062>064.