textproduct: Pocatello

KEY MESSAGES

- Terrain Convection Today: Building high pressure suppresses organized forcing, but lingering monsoonal moisture will spark isolated to scattered afternoon showers and storms over the mountains, with a low-end chance of an isolated cell spilling into the Snake Plain. Main threats are gusty outflow winds and brief moderate downpours.

- Mid-to-Late Week Heat Surge: Temperatures will steadily rise, reaching the low-to-mid 90s across lower valleys Thursday and Friday.

- Weekend Pattern Uncertainty: Ensemble guidance hints at a deep Pacific Northwest low shifting the ridge east over the weekend, potentially re-opening the monsoonal moisture tap. Given high model variance regarding ridge placement, a consensus middle-of-the-road forecast is maintained for now.

DISCUSSION

Issued at 300 PM MDT Mon Aug 17 2026

An upper-level ridge of high pressure will continue building across southeastern Idaho today. While this building ridge will eliminate large-scale upper-level support for organized convection, deep monsoonal moisture remains firmly entrenched across the region. Driven by increasing surface temperatures under the ridge, diurnal heating is leading to another afternoon of isolated to scattered higher-terrain showers and thunderstorms. High-resolution convective-allowing models (CAMs) strongly support this terrain-driven convective placement for this afternoon and evening, though at least an isolated chance remains for activity or gusty outflows to push into the Snake Plain. The primary hazards with any developing cells will be localized gusty outflow winds and brief, moderate downpours. Convective activity will taper off quickly this evening with the loss of solar heating.

Convective potential picks up slightly tonight into Tuesday as a shortwave trough traverses the northern perimeter of the ridge across Montana. Associated height falls and glancing upper- level energy will enhance shower and thunderstorm coverage across eastern Idaho during this timeframe, particularly over the Central Mountains, Continental Divide, and Eastern Highlands. NBM guidance appeared too low given the incoming dynamics, so PoPs were manually adjusted upward to better reflect expected coverage.

Behind the departing shortwave, the ridge amplifies and this will shut off the monsoonal moisture plume pushing a drier air mass into the Intermountain West and significantly reducing daily thunderstorm chances for the second half of the week. Daytime temperatures will steadily trend upward Wednesday into Friday. Expect afternoon highs to remain slightly below seasonal normals through Tuesday before surging above average, especially Thursday and Friday, as the ridge axis locks over the region with low-to-mid 90s looking increasingly likely across valley locations.

Though there is some uncertainty, by next weekend model ensembles show a deep Pacific Northwest low shifting the ridge eastward. This would open the door for the return of monsoonal moisture, bringing returning precipitation chances and cooler temperatures. However, significant model differences remain regarding the exact placement and strength of the Great Basin ridge, so a middle-of-the-road approach remains the forecast for now until better consistency is seen in model guidance.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1049 AM MDT Mon Aug 17 2026

Maintaining same afternoon PROB30s in the latest forecast update. Have opted to keep it in the KIDA TAF, although confidence is lowest here for any thunderstorm activity (around 20 to 30 percent), with a 30 to 40 percent chance at KPIH, KBYI, and KDIJ. There is less than 20 percent chance at KSUN and therefore have maintained no mention of thunder in the forecast. Thunderstorms will be capable of gusts 35 to 45 mph.

FIRE WEATHER

Issued at 1248 PM MDT Mon Aug 17 2026

Monsoon moisture advected northward in southwest flow aloft will bring us another round of isolated storms today mostly across the mid to high elevations. High resolution models show activity remaining north and south of the Snake River Plain this afternoon with isolated showers and storms working across the Snake River Plain during the early evening. Thunderstorms will be capable of heavy rain and wind gusts up to around 45 mph.

A shortwave feature passing to our north tonight and Tuesday will flatten the ridge, keeping activity going along the Montana Divide overnight and again Tuesday afternoon while keeping temperatures just below normal. The ridge will rebound on Wednesday, which will allow us to warm back into above-normal territory later week. As the ridge of high pressure shifts directly overhead, many low elevation areas will warm into the 90s on Thursday and Friday. While the details are still in flux, ensembles show a deep PacNW low shifting the ridge eastward this weekend and opening the door for the return of monsoon moisture.

PIH WATCHES/WARNINGS/ADVISORIES

None.