textproduct: Pocatello

KEY MESSAGES

- Unseasonably Cool & Active Weekend: Strong southwesterly flow between a West Texas ridge and a digging Pacific Northwest trough will draw deep moisture into eastern Idaho, keeping temperatures 10 to 15 degrees below normal (highs in the 60s and 70s) alongside widespread rain through Saturday.

- Saturday Severe Thunderstorm Risk: The Storm Prediction Center (SPC) has placed all of eastern Idaho in a Marginal Risk for severe storms on Saturday, with a localized Slight Risk across the far southeast corner (Pocatello south to the Utah border). Strong QG ascent, effective bulk shear exceeding 40 knots, and CAPE greater than 1000 J/kg will support supercells capable of localized severe wind gusts.

- Weekend Rainfall Distribution: Total precipitation through Sunday will range from ~0.10" across the central mountains and western zones to 0.25"0.50" in the Snake Plain, and 0.50"1.00" across the Eastern Highlands.

- Fall-Like Early September: Broad troughing will persist over the Pacific Northwest through next week, keeping daytime highs cool and dropping overnight lows into the 40s and low 50s across lower elevations.

DISCUSSION

Issued at 248 AM MDT Fri Aug 28 2026

Early morning satellite imagery reveals increasing cloud cover and moisture streaming across the northern Great Basin as eastern Idaho resides between a broad ridge over West Texas and a digging upper-level trough over the Pacific Northwest. Strong southwesterly flow aloft will overspread the region with Pacific moisture over the next few days, maintaining cool temperatures and high precipitation chances through the weekend. High- resolution convective-allowing models (CAMs) show widespread precipitation filling in around sunrise, followed by a brief early afternoon lull before a second, deeper moisture surge arrives this evening and overnight. While overall convective parameters today are modest, stronger cells will remain capable of producing localized gusty winds and small hail. Increased cloud shading and falling 500 mb heights will cap today's maximum temperatures in the 70s, with only isolated spots reaching the lower 80s.

The upper-level low will shift into central and eastern Washington on Saturday, continuing to lower H5 heights and holding daytime highs in the 60s and 70s. Despite the cool surface readings, strong upper-level forcing will support organized convection. The Storm Prediction Center (SPC) has designated a Marginal Risk for severe storms across all of eastern Idaho, with a Slight Risk focused across the far southeastern corner from Pocatello south toward the Utah border. This region aligns with a focused corridor of strong QG ascent immediately ahead of the main trough axis.

Short-range guidance exhibits subtle thermodynamic variance: the RAP depicts rich low-level moisture with dewpoints nearing 60, mid-level lapse rates exceeding 7.5 C/km, and MLCAPE over 2000 J/kg, while the NAM maintains drier surface dewpoints in the upper 40s to 50s and slightly less steep lapse rates. Nevertheless, both models agree on peak MLCAPE exceeding 1000 J/kg alongside elongated hodographs and effective bulk shear over 40 knots, establishing an environment conducive to rotating supercells capable of severe downburst winds.

The system begins to exit on Sunday as the primary low swings across northern Montana and southern Alberta. Cloud cover and precipitation coverage will diminish from west to east throughout the day, while temperatures remain seasonably cool in the 60s and 70s. Storm-total precipitation from Friday through Sunday is forecast to range from around 0.10" across the central mountains and western zones, 0.25" to 0.50" across the Snake Plain, and 0.50" to 1.00" across the Eastern Highlands. Given the convective nature of the event, localized totals may vary based on thunderstorm tracks.

Temperatures will moderate slightly on Monday as weak ridging attempts to build overhead, allowing a few lower elevation spots to touch 80F while most remain in the upper 70s. However, ridging will remain short-lived as global guidance maintains broad troughing over the Pacific Northwest throughout next week. Multiple shortwave impulses tracking through this cyclonic flow will preserve low-end daily precipitation chances and hold temperatures on the cool side of average. Overnight lows will drop noticeably into the 40s and lower 50s across valley floors, ushering in a crisp, fall-like environment for the start of September.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 549 AM MDT Fri Aug 28 2026

Clouds and showers in place throughout the region this morning. VCSH in place accordingly with prob30 thunder again after 20Z at all sites Friday afternoon and predominant showers after 00Z as a series of upper level short waves bring in moisture in strong southwesterly flow aloft throughout Friday night and into Saturday AM. Ceilings expected to remain VFR level through the shower and thunderstorm periods. Synoptic winds should be generally unimpactful but TSTM gusts could prove problematic if/when a storm gets close to an airfield.

FIRE WEATHER

Issued at 248 AM MDT Fri Aug 28 2026

The regional fire weather regime undergoes a significant transition over the next 24 to 48 hours. Today represents the final day of isolated, gusty afternoon convection driven by dry sub-cloud air. Beginning Friday and continuing through Sunday, a deep surge of moisture overspreads eastern Idaho, resulting in widespread shower and thunderstorm activity. While lightning frequency will increase, storm character will shift to efficient, wetting rainfall producers. Accompanied by higher relative humidity recoveries and a dramatic cooldown into the 70s for the weekend, widespread critical fire weather conditions are not anticipated Friday through Sunday.

PIH WATCHES/WARNINGS/ADVISORIES

None.