textproduct: Pocatello

KEY MESSAGES

- Terrain-Driven Convection Today: An amplifying ridge removes large-scale forcing, but entrenched monsoonal moisture will support mainly isolated afternoon thunderstorms over the mountains and highlands, producing localized gusty winds and brief moderate downpours.

- Slightly Enhanced Storm Potential Tuesday: A shortwave trough tracking through Montana across the top of the ridge will slightly increase shower and thunderstorm coverage, primarily over northern and eastern high country.

- Late-Week Drying & Heat Surge: Northwesterly flow behind the departing shortwave will dry out the atmosphere for the second half of the week, with an amplifying ridge pushing lower- valley temperatures back into the 90s.

DISCUSSION

Issued at 241 AM MDT Mon Aug 17 2026

An upper-level ridge of high pressure will continue building in 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 diurnal surface heating, mostly isolated, higher terrain afternoon thunderstorms will develop. High-resolution convective-allowing models (CAMs) strongly support this terrain-driven convective placement. 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.

A shortwave trough is forecast to traverse the northern perimeter of the ridge, moving across Montana from Monday night through Tuesday. Associated height falls and glancing upper- level energy will slightly enhance shower and thunderstorm coverage across eastern Idaho during this timeframe, particularly over the Central Mountains, Continental Divide, and Eastern Highlands.

Behind the departing shortwave, upper-level flow will shift to the northwest as the ridge amplifies just to our west. This northwesterly trajectory will shunt the primary monsoonal moisture plume southward, 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 Thursday and Friday as the ridge axis locks over the region. Lower-elevation valley locations, including the Snake Plain and Magic Valley, will see a return to the 90s by late week.

Though there is some uncertainty, by next weekend model ensembles show a deep PacNW low shifting the ridge eastward. This would open the door for the return of monsoon moisture, which would bring the return of precipitation and cooler temperatures.

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.