textproduct: Pocatello

KEY MESSAGES

- A Passing Wave to our North brings Convection Today: Building high pressure suppresses organized forcing, but lingering monsoonal moisture and a passing wave to our north will spark mostly isolated showers and storms mainly 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 1225 PM MDT Tue Aug 18 2026

A shortwave feature passing to our north today will flatten the ridge of high pressure over Idaho. This will keep isolated showers and thunderstorms in the forecast today, particularly along the Montana Divide region and eastern mountains. We have continued to increase PoPs above National Blend amounts to reflect convection today depicted in high resolution models. The Storm Prediction Center has included the northeastern corner of our CWA, including Island Park and Driggs, in a Marginal Risk of severe weather with a general risk of thunder extending from the MT Divide to Idaho Falls southward to Preston. The main impacts will be wind gusts to around 45 mph and small hail.

Dry conditions are in store for mid- to late week as the ridge rebounds tomorrow, allowing us to warm back into above-normal territory late this week. The warming trend will continue through Friday, with widespread 90s across our lower elevations by Thursday when the ridge axis shifts directly overhead. 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. The ECMWF ensemble indicates precipitation as early as Thursday afternoon while the GFS ensemble maintains dry conditions areawide until Friday afternoon. Saturday will be the busiest weather day for Southeast Idaho, with scattered thunderstorms for portions of the region, but the active pattern will continue into at least the first part of the next week as low pressure remains off the coast with an area of high pressure set up over the Southwest.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1136 AM MDT Tue Aug 18 2026

A shortwave trough working through Montana will bring isolated convection to Southeast Idaho. Have maintained PROB30s for KIDA and KDIJ this afternoon with dry conditions elsewhere. High resolution models show activity remaining outside of all other terminals. Winds will be slightly elevated, up to around 12 kts outside of KBYI and KSUN.

FIRE WEATHER

Issued at 1225 PM MDT Tue Aug 18 2026

A shortwave trough passing through Idaho today brings isolated thunderstorm chances to much of the higher elevation areas through the afternoon and evening hours. The main threat with storms today will be gusty winds of 50+ mph with a Marginal Risk for severe weather in part of the upper Snake River Plain near the Montana Divide and Island Park area. This little bit of moisture around will keep our temperatures nearly identical to yesterday. Tomorrow, a ridge of high pressure builds in over the area and means temperatures begin to warm again with highs in the 80s to low 90s for most and min RHs generally at or below 20 percent. Winds look to remain on the lighter side during the "dry" time of Wednesday and Thursday, so we are expected to stay below Red Flag warning criteria at this point. Models are hinting at some isolated thunderstorms returning to the higher elevations as early as Thursday afternoon, but those look VERY isolated at this point with some increasing, but still isolated activity returning on Friday as monsoon moisture returns to the area. This activity picks up as high pressure over the Four Corners region is pushed just a bit eastward by an area of low pressure moving into the Pacific Northwest. That low moves northeastward over the weekend and Saturday looks to be the most active day for our area, so we will watch it as the next best chance for needing any Red Flag warnings for scattered thunderstorm coverage. Activity continues on Sunday, but appears to be a bit more isolated once again. Next week there is some disagreement on how systems will behave, but with high pressure remaining over New Mexico and Texas and troughing off the West Coast, we keep the door open for more moisture to keep working into the area each at least through Monday and Tuesday.

PIH WATCHES/WARNINGS/ADVISORIES

None.