textproduct: Pocatello

KEY MESSAGES

- Dry Daytime, Evening Storms: High-resolution models keep eastern Idaho dry through the daytime hours today. Shower and thunderstorm chances will hold off until early this evening, with precipitation potentially lingering into early Tuesday morning.

- Tuesday's Focus Shifts North: A secondary weather system will move into western Idaho on Tuesday, shifting the best chances for showers and thunderstorms toward the Central Mountains and the Continental Divide.

- Breezy & Seasonably Cool Mid-to-Late Week: A large low- pressure system anchoring near Vancouver Island will keep persistent westerly flow over the region Wednesday through Friday. Expect daily breezy afternoon winds and temperatures hovering near or just below early September normals.

- Unsettled Labor Day Weekend: An upper-level low over the Pacific Northwest may bring unsettled weather for the holiday weekend, though forecast confidence regarding exact impacts and precipitation timing remains low due to high model spread.

DISCUSSION

Issued at 257 AM MDT Mon Aug 31 2026

Following a chilly August morning where efficient radiational cooling allowed high-altitude basins to drop into the 30s and lower valleys into the 40s, eastern Idaho remains under the influence of a broad upper-level trough over the Pacific Northwest. Based on the latest convective-allowing models (CAMs), the region will remain precipitation-free through the daytime hours. Afternoon maximum temperatures will generally reach the 70s to lower 80s across lower elevations. Moisture and atmospheric lift will increase by early evening, initiating isolated to scattered showers and thunderstorms. This activity will primarily target the eastern half of the forecast area and is expected to continue through the overnight hours, potentially lingering into early Tuesday morning.

As Monday night's precipitation clears out, a secondary, impulse embedded within the upper flow is slated to approach western Idaho later on Tuesday. The trajectory of this impulse will shift the primary axis of atmospheric lift and moisture further north. Consequently, precipitation probabilities on Tuesday will be highest across the Central Mountains and northward toward the Montana Divide and across the upper Snake Plain while locations further south and east see more limited coverage. Temperatures will remain steady in the 70s to lower 80s.

By mid-to-late week, global ensemble guidance is in good agreement locking a broad upper-level cyclone near Vancouver Island, maintaining persistent cyclonic flow across the Intermountain West. Current guidance suggests the bulk of the deep atmospheric moisture will remain shunted north and west of eastern Idaho from Wednesday through Friday, though localized mountain showers cannot be ruled out. Tightening pressure gradients ahead of incoming Pacific impulses will result in several breezy afternoon periods mid-to-late week. For now, National Blend of Models (NBM) guidance maintains afternoon temperatures at or a few degrees below seasonal averages through the end of the workweek.

Looking ahead to the holiday weekend, models indicate an upper- level low situated somewhere across the Pacific Northwest. This pattern has the potential to bring unsettled weather and cooler temperatures to eastern Idaho for Labor Day. However, confidence in the exact evolution of this upper-level pattern remains low at this time due to significant ensemble spread. We will continue to monitor trends as the weekend approaches to refine precipitation chances and timing.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1028 AM MDT Mon Aug 31 2026

The risk of TSRA at the 5 airdromes has fallen considerably for tonight. The arrival of moisture has slowed to a later time: after midnight for KIDA, KPIH, and KDIJ, while the two eastern airdromes are 01/01Z for KBYI and probably not at all at KSUN. When the moisture arrives, the farther east, the lower the CIG. KDIJ has a very low chance of marginal VFR after 01/14Z, which is near the end of the forecast period. The farther east, the better the consistency of -SHRA as well.

Except for KPIH, which appears to have a chance for G20KT, the rest of the TAFs have a northerly light flow shifting to a southerly light flow, with periods of VRB04KT in between. KSUN has the usual slope-valley wind interactions, maybe getting up to 10KT during the late night and morning hours.

FIRE WEATHER

Issued at 135 PM MDT Mon Aug 31 2026

A mass of moisture is moving in from the south, arriving in southern Idaho in the early evening and in eastern Idaho around midnight, and central Idaho around Tuesday morning. Thunderstorms should develop by at least Tuesday afternoon with scattered coverage in the central Idaho mountains and the northern end of the Snake River plain. Red Flag Warning was issued for the norther portions of the Sawtooth NF. The higher threat of wetting rains in the northern half of the Snake River plain have made the lightning activity of lower threat.

The incoming moisture will mean cloudiness that will keep temperatures relatively cool, and thus humidity readings should be way up, at least for a little. May have to watch Fire Weather Zone 427 on Wed as humidity dries out first there, at the same time as wind increase to breezy to windy conditions.

Warming and drying develop for the middle part of the week, with Sunday being the next day of significant shower and thunderstorms activity.

PIH WATCHES/WARNINGS/ADVISORIES

Red Flag Warning from 1 PM to 9 PM MDT Tuesday for IDZ422.