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 220 AM MDT Tue Aug 18 2026

Convective activity picks up slightly this morning and continues through today, especially this afternoon, 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 today before surging above average, especially Thursday and Friday, as the high pressure 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 /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 522 AM MDT Tue Aug 18 2026

Expect VFR conditions during the period with overall light winds. A passing wave to the north this morning will bring VCSH showers for BYI and PIH. Models continue the best chance of thunderstorms this afternoon/early evening is across our northern areas. Have a PROB30 for thunderstorms this afternoon/early evening for DIJ and IDA with gusts of around 30 kts possible with any thunderstorms. There is less than a 10 percent chance for thunderstorms for SUN and BYI and less than a 20 percent chance of thunderstorms for PIH this afternoon. Starting early this evening expect light winds and clearing skies as high pressure builds in.

FIRE WEATHER

Issued at 220 AM MDT Tue Aug 18 2026

A shortwave feature passing to our north today will flatten the high pressure ridge keeping convective, mostly isolated, activity going across higher terrain today, especially along the Montana Divide. Today, expect temperatures slightly below normal.

The high pressure ridge will rebound on Wednesday, which will allow us to warm back to above-normal temperatures 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, model ensembles show a deep PacNW low shifting the ridge eastward this weekend and opens the door for the return of monsoon moisture.

PIH WATCHES/WARNINGS/ADVISORIES

None.