textproduct: Boise

KEY MESSAGES

- Heat Advisories in the Snake Plain today and tomorrow.

- Showers and thunderstorms return Monday evening through the week, with peak coverage Tuesday afternoon.

- Tuesday storms will be capable of heavy downpours, potentially affecting steep terrain and burn scars.

- Hot temperatures remain through the week.

SHORT TERM /Through Tuesday Night/

High pressure to the east continues warm and dry southwesterly flow aloft, although a monsoonal moisture tap is bringing increasing clouds today. Clouds today will moderate the high temperature relative to yesterday, but will also limit cooling tonight. As the warm flow continues so does the warming trend, bringing the Snake Plain back into 100 degree territory. Today, a Heat Advisory is in effect for the Magic Valley. Tomorrow, the warmer temperatures have prompted an expansion of the Advisory to include the rest of the Snake Plain including the Treasure Valley. Max temperatures in the high 90s up to 101 degrees are expected tomorrow.

The warming trend hits a plateau after Monday as the monsoonal moisture tap brings increasing chances of precipitation and steady cloud cover. Precipitable water increases from the 90th percentile Monday up to the 99th percentile Tuesday. This reflects the trend in precipitation chances well, as there is a 10% chance of precipitation and a 10% chance of thunder on Monday. Storms will begin drier initially and become wetter into the evening, although a 25-45 mph storm motion will limit accumulation. Chances increase with more available atmospheric moisture on Tuesday, with a 40% chance of precipitation and a 20% chance of thunder. Precipitation is less likely in the Treasure Valley and Weiser Basin. While storms on Tuesday will be more efficient rain producers than storms on Monday, a fast storm motion will limit accumulation over any given spot. This being said, vulnerable areas such as burn scars and steep slopes still have a minor risk for flash flooding and debris flows. Rainfall amounts directly under showers on Monday could see up to 0.25 inches of rain in an hour, while on Tuesday up to 0.5 inches in an hour is possible. Storms both days will be capable of gusty outflow winds and cloud to ground lightning. Temperatures cool slightly to around normal Tuesday, with max temps in the Snake Plain in the mid 90s.

LONG TERM /Wednesday through Sunday/

Ensembles and clusters have finally (largely) agreed on bringing the upper-level shortwave in the Pacific onshore Wednesday into Thursday. While this won't completely shove the moisture fetch from the monsoon to the east, it will limit higher shower and thunderstorm chances to the higher terrain mainly over the SW Idaho mountains. Despite this shortwave moving through the region, southerly/southwesterly flow aloft will be maintained with the upper- level ridge not being deterred over the Four Corners region. PWAT values at or above 0.8" areawide will continue the primary concern of flooding, although this far out in the forecast period, location and timing is very uncertain. Model solutions begin to diverge again Friday through the weekend, with the amplitude of the ridge in question as well as possible troughing again off the Pacific NW shoreline. Monsoonal moisture will still permeate through the Great Basin, but its northward extent is the primary question, leading to low forecast confidence of showers/thunderstorms within the forecast area. Overall, slight chances for precipitation linger over higher terrain as hot, south-southwest flow attempts to dominate through the weekend. Surface max temperatures should remain 5-10 degrees above normal through the forecast period.

AVIATION /18Z Sunday through Monday/

Issued 1201 PM MDT SUN JUL 12 2026

VFR. Increasing high clouds/virga, and a 10% chance of light rain in E Oregon this PM. Areas of reduced visibility from wildfire smoke/haze, especially near KBKE. High density altitude due to heat. Surface winds: SW-NW 5-15 kt this afternoon, and gusts to 20-30 kt for portions of E Oregon and Snake Plain. Winds aloft at 10kft MSL: S-SW 15-30 kt.

KBOI...VFR and high clouds/virga. Visibility reduced at times by wildfire smoke in foothills NE of KBOI. High density altitude due to heat. Surface winds: W to NW 5-15 kt. Occasional afternoon gusts around 20 kt.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Heat Advisory from 2 PM to 9 PM MDT Monday for IDZ012-014. Heat Advisory until 9 PM MDT Monday for IDZ016-030. OR...Heat Advisory from 2 PM MDT /1 PM PDT/ to 9 PM MDT /8 PM PDT/ Monday for ORZ064.