textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Hot temperatures this week, hottest today with a Heat Advisory in the Snake Plain and high desert.

- Isolated to scattered showers and thunderstorms near the Idaho/Nevada border today.

- Showers/thunderstorms increase through midweek with heavy rainfall possible especially on Wednesday.

- Areas of smoke through the week.

SHORT TERM /Through Wednesday Night/

Issued 314 AM MDT MON JUL 20 2026 An upper level ridge centered over the Southern Rockies will build north today, bringing hotter temperatures to our area. Highs will reach the upper 90s to 105 degrees in the lower valleys, and a Heat Advisory remains in effect for much of the lower elevations across the Snake Plain and high desert. Additionally, low temperatures this morning and again tonight will only dip into the upper 60s to lower 70s in these locations, limiting relief from the heat. Smoke from Oregon wildfires may prevent some locations from reaching their full heating potential. However, some improvement in smoke is likely this afternoon as the flow aloft becomes southerly. Southerly flow will also transport monsoonal moisture into our area. Mid to high clouds and virga/isolated showers will lift north across the area this morning with partial clearing in the afternoon. Isolated to scattered showers and thunderstorms will develop near the Idaho/Nevada border this afternoon and evening, with gusts to 40 mph possible. Outside of storms, breezy conditions will develop late today with gusts 15-30 mph, locally up to 40 mph in eastern Oregon this evening.

Moisture will continue to increase Tuesday with shower/storm potential expanding across higher elevations. By Wednesday, precipitable water values will rise to around 1.25 inches, above the 95th percentile. An embedded shortwave trough will interact with this moisture, increasing shower and thunderstorm coverage, especially across eastern areas where precipitation chances will reach 30-70%. The higher terrain across southeast Oregon and far southwest Idaho will see a 20-40% chance of precipitation with a less than 20% chance in the lower valleys. With deep moisture in place and slow expected storm motion, thunderstorms will be capable of heavy rain and flash flooding, especially over burn scars and steep terrain.

Temperatures Tuesday and Wednesday will be a few degrees lower due to the increasing moisture, but it will still be hot. Winds will be locally breezy each afternoon. With southerly flow aloft, smoke should improve each afternoon, but northwest surface winds may transport smoke back into the area each night.

LONG TERM /Thursday through Monday/

Issued 314 AM MDT MON JUL 20 2026 The pattern will shift once again during the extended. On Thursday, an upper level trough off the Pacific Northwest coast will begin to deepen, turning the flow aloft southwesterly. This will push monsoonal moisture to the east and usher in a much drier airmass. Shower/storm chances will decrease through the end of the week, and by Sunday will be less than 20% in all areas. Southwest flow will keep temperatures hot, with lower valley highs in the upper 90s to around 100 degrees. The trough will bring breezy conditions each day with gusts 15-30 mph. Smoke may impact the area through the period, especially across southeast Oregon.

AVIATION /12Z Monday through Tuesday/

Issued 600 AM MDT MON JUL 20 2026 Mainly VFR. Wildfire smoke across the area resulting in localized MVFR/IFR visibility, mainly in E-Oregon and near KEUL. Some improvement this afternoon. Isolated showers/virga lifting north through SE Oregon and W-Central Idaho this morning. Isolated to scattered showers and thunderstorms near the Idaho/Nevada border this afternoon and evening, gusts up to 35 kt possible. Afternoon high density altitude due to heat through the week. Surface winds: variable less than 10 kt this morning, then NW-N 10-15 kt with localized gusts to around 25 kt this afternoon and evening. Winds aloft at 10kft MSL: Variable 5-15 kt.

KBOI...VFR. Visibility reductions due to wildfire smoke, although VFR expected to prevail. Scattered showers/virga late tonight. Afternoon high density altitude this week due to heat. Surface winds: light and variable this morning, then NW 10-15 kt with gusts to 20-25 kt this afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Heat Advisory from noon today to 9 PM MDT this evening for IDZ012-014>016-030-033. OR...Heat Advisory from noon MDT /11 AM PDT/ today to 9 PM MDT /8 PM PDT/ this evening for ORZ063-064. Air Quality Alert until noon PDT today for ORZ061-062.