Sunrise 6:15 AM   Sunset 9:07 PM Moonrise 2:25 PM   Moonset 2:48 AM

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FXUS65 KBOI 170907 AFDBOI

Area Forecast Discussion National Weather Service Boise ID 307 AM MDT Fri May 17 2024

SHORT TERM
Today through Sunday night...The pattern transitions to an upper-level trough over western Canada beginning today, which will persist through the short term.

The first shortwave will move across the northern Rocky Mountains later today, preceded by a cold frontal passage later this morning. The associated cold front will sweep southeast across southeast Oregon by 7 AM MDT and southwest Idaho between sunrise and 11 AM. Wind speeds will increase behind the front and will continue through the evening, with the strongest winds expected from Mountain Home through the Western Magic Valley, Camas Prairie, and Southern Twin Falls County. Wind gusts up to 50 MPH are possible, as indicated by the current Wind Advisory in this area. Although moisture is limited with the frontal passage, there is a 20% chance of showers along the frontal boundary over the higher terrain of the West Central Mountains of Idaho this morning. Temperatures today will be about 5 degrees below normal, with valleys reaching the upper 60s, which is approximately 15-18 degrees cooler than yesterday (Thursday’s) highs.

A cold west-northwesterly flow will persist through Saturday as the area remains between shortwaves, allowing temperatures to reach normal. The next shortwave will move across the area from Saturday evening into Sunday, bringing another cold front. This system is stronger and colder than the previous one, causing temperatures to drop about 10 degrees below normal and bringing gusty westerly winds, especially in the Western Snake River Plain. Additionally, there is about a 30% chance of showers across the West Central and Boise Mountains of Idaho, with light snow possible above 6000 feet.

LONG TERM
Monday through Friday...Cool, unstable, and breezy northerly flow will develop over the forecast area on Monday as a trough passes through the Intermountain West. A 20-40% chance of showers will persist over the southwest Idaho mountains through Monday evening, though temperatures should rebound a few degrees from Sunday's high temps. A brief, weak ridge will follow early Tuesday before the next trough arrives Tuesday night into Wednesday. Shower chances will increase over E Oregon and SW Idaho Wednesday, especially over the Idaho terrain, along with a slight chance (15%) of afternoon mountain thunderstorms as instability increases. Snow levels are forecast to lower to 5000-6000 ft MSL by late Wednesday. Models begin to vary significantly on the path and evolution of this trough, and subsequent troughs, for the remainder of the week. However, the overall pattern should maintain an active period across the region, along with more days of below normal temperatures.

AVIATION
VFR. Isolated showers along a cold front in northeast OR and w-central ID, decreasing by Fri/18Z. Local visibility reduction from smoke near prescribed fires, mainly over the southwest Idaho mountains. Surface winds: SW to NW 5-15 kt, becoming W to NW 15-25 kt with gusts to 25-40 kt by late this morning/aftn. Winds aloft at 10kft MSL: W to NW 25-40 kt.

KBOI...VFR. Hazy skies due to the prescribed fires in the Boise Mountains. Surface winds: W-NW 5-10 kt, becoming NW 15-20 kt with gusts 25-30 kt around Fri/15Z. Winds will decrease to 5-10 kt after sunset, then variable up to 6 kt by Sat/06Z.

Weekend Outlook...VFR. Chance (20-50%) of showers in the central ID mountains on Sunday. Snow levels 4500-5500 ft MSL. Surface winds mainly SW to NW 10-20 kt with gusts to 25-35 kt for Sat/Sun.

BOI WATCHES/WARNINGS/ADVISORIES
ID...Wind Advisory from 9 AM this morning to 9 PM MDT this evening IDZ014-016-028-030.
OR...None.

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