textproduct: Pocatello

KEY MESSAGES

- Flash Flood Risk & Active Flood Watches: Deep monsoonal moisture carrying Precipitable Water (PWAT) values near the 99th percentile has prompted a Flood Watch for the Eastern and Southeastern Highlands, as well as the Wapiti Burn Scar in the Central Mountains. Slow-moving thunderstorms through Wednesday will be capable of torrential rainfall, localized flash flooding, and debris flows on recent burn scars. Secondary storm hazards include gusty outflow winds and small hail.

- Peak Moisture Window Today & Wednesday: This 2436 hour stretch represents the wettest period of the 7-day forecast. Extensive cloud cover will keep daytime highs limited to the 80s in lower elevations and mid-to-upper 70s in the mountains. - Late-Week Pattern Shift & Returning Heat: A drying and warming trend begins Thursday. High temperatures will climb back into the mid-90s across lower valleys this weekend and into early next week.

DISCUSSION

Issued at 147 PM MDT Tue Jul 21 2026

A robust plume of monsoonal moisture continues to surge into eastern Idaho this afternoon, setting the stage for an active 24 to 36 hours across the region. Isolated to scattered showers and thunderstorms will continue to develop through the remainder of the afternoon and persist into the early overnight hours. While a brief lull in convective coverage is possible early Wednesday morning, a secondary, potent wave of deep atmospheric moisture will stream into the area shortly thereafter.

Precipitable Water (PWAT) values on Wednesday will climb well above climatological norms, approaching the 99th percentile for late July. This atmospheric profile will yield exceptionally efficient, heavy-rainfall-producing showers and thunderstorms. Given the slow movement of these storms and high rain rates, localized flash flooding is a major concern. Consequently, a Flood Watch has been issued for the Eastern and Southeastern Highlands, as well as the Wapiti Burn Scar across the central mountains where debris flows will be a heightened risk. While the watch area currently encompasses the highest confidence for heavy rain, areas outside the watch across eastern Idaho remain vulnerable to localized flash flooding if slow-moving cores track directly overhead. Widespread cloud cover and precipitation will limit diurnal heating, capping Wednesday highs in the 80s for lower elevations and the mid-to-upper 70s across higher terrain. Gusty outflow winds and small hail will also accompany stronger cells.

Wednesday into Wednesday night will mark the wettest phase of the 7-day period. Beginning Thursday, the main monsoonal moisture axis will end, initiating a transition back to a warmer and drier pattern heading into the weekend and early next week. While lingering mid-level moisture will maintain low-end daily shower and thunderstorm chances over the higher terrain, overall convective coverage will be isolated. Heat will quickly re- emerge as the primary operational impact, with high pressure building back over the Intermountain West to push lower- elevation afternoon highs back into the mid-90s as early as Friday and continuing into early next week and likely much longer.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 526 PM MDT Tue Jul 21 2026

Currently there is a strong thunderstorm for DIJ creating IFR/MVFR conditions along with heavy rain. PROB30 for thunderstorms remains in the TAF at all sites except SUN for this evening. Most storms that get going will likely just be breezy with gusts of 20 to 25 kts. However, any stronger storm that does get going, could produce strong gusts around 25 to 35kts. The thunderstorm over DIJ should be out of the area in the next hour. BYI has the best chance of storms developing the next hour or two. However, outflows could bring a storm to IDA and, to a lesser degree, PIH in the next couple of hours. So, have left thunderstorms chances in for all sites except SUN (DIJ for just one more hour). Expect light showers mostly in the vicinity for all sites overnight.

Showers and storms increase in coverage tomorrow and storms on Wednesday aren't expected to produce as strong of wind gusts since they will produce more rain. Have put in a PROB 30 for thunderstorms for all TAF sites for tomorrow afternoon.

FIRE WEATHER

Issued at 147 PM MDT Tue Jul 21 2026

Monsoon moisture continues to bring isolated to nearly scattered showers and thunderstorms to portions of Fire Weather Zones 413, northern 422, 427, 475, and 476 this afternoon. Coverage actually begins to increase later this evening, after 1800 MDT. Stronger storms today will be capable of producing strong wind gusts of 40 to 50 mph and will be a mix of wet and dry storms.

Moisture content increases in a big way on Wednesday with PWATs ranging from almost 1.00 to 1.50 inches across all of our coverage area, much higher than normal for this time of the year. With the better chance for any storm to produce a wetting rain, the wind threat diminishes for Wednesday with gusts more likely around 35-45 mph. Given how wet these storms will be, we have opted to NOT issue a Red Flag Warning even though we will reach "scattered" thunderstorm criteria at almost every Fire Weather Zone on Wednesday. So, expect showers and thunderstorms producing lightning, but also producing a wetting rain. We will be watching the Wapiti burn scar for flash flooding potential as well as watching the Ohio fire area for any flash flooding there, too.

On Thursday, isolated thunderstorms will linger in the Central Mountains and Eastern Highlands, and while we won't completely shut off our monsoons moisture for Friday and the weekend, it will be much drier overall. Winds begin to increase on Friday and Saturday afternoons with gusts of 25 to 35 mph and afternoon min RHs falling into the teens and 20s.

PIH WATCHES/WARNINGS/ADVISORIES

Flood Watch from Wednesday afternoon through Wednesday evening for IDZ058>066.