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 /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 558 AM MDT Mon Aug 17 2026

VFR conditions with overall light winds are expected at all TAF sites. Biggest impact continues to be the slight chance of afternoon thunderstorms with gusty outflow winds of 40 to 45 kts at all TAF sites except SUN. SUN has less than a 10% chance of tstms. There is a 30 to 40% chance of tstms at BYI, PIH and IDA. DIJ has a 50 to 60% chance of afternoon tstms. Have kept the PROB30 afternoon/early evening line for tstms for all TAF sites except SUN.

FIRE WEATHER

Issued at 241 AM MDT Mon Aug 17 2026

A ridge of high pressure will continue building over the region today, although monsoon moisture will still be abundant enough to support isolated, mostly mountain, convection this afternoon. Thunderstorms will be capable of moderate rain and wind gusts up to around 45 mph.

A shortwave feature passing to our north will flatten or weaken the high pressure ridge on late Monday into Tuesday before the high pressure ridge rebounds mid-to-late week. This will mean slightly cooler temperatures and isolated to scattered, mostly mountain, convection over our northern and eastern areas on Tuesday. Then, expect drier conditions Wednesday into Friday along with near normal to slightly above normal temperatures.

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.

PIH WATCHES/WARNINGS/ADVISORIES

None.